fix ci

* feat: vue support

* feat: add a vite example

* use css instead of inline styles

* feat: add tests

* chore: use portless

* fix: update reactivity

* chore: update

* chore: build

* feat: add hooks, add missing zod peer deps

README.md

@@ -5,15 +5,18 @@
 Generate dynamic, personalized UIs from prompts without sacrificing reliability. Predefined components and actions for safe, predictable output.
 
 ```bash
+# for React
 npm install @json-render/core @json-render/react
-# pre-built shadcn/ui components
+# for React with pre-built shadcn/ui components
 npm install @json-render/shadcn
-# or for mobile
+# or for React Native
 npm install @json-render/core @json-render/react-native
 # or for video
 npm install @json-render/core @json-render/remotion
 # or for PDF documents
 npm install @json-render/core @json-render/react-pdf
+# or for Vue
+npm install @json-render/core @json-render/vue
 ```
 
 ## Why json-render?
@@ -23,7 +26,7 @@ json-render is a **Generative UI** framework: AI generates interfaces from natur
 - **Guardrailed** - AI can only use components in your catalog
 - **Predictable** - JSON output matches your schema, every time
 - **Fast** - Stream and render progressively as the model responds
-- **Cross-Platform** - React (web) and React Native (mobile) from the same catalog
+- **Cross-Platform** - React, Vue (web), React Native (mobile) from the same catalog
 - **Batteries Included** - 36 pre-built shadcn/ui components ready to use
 
 ## Quick Start
@@ -110,6 +113,7 @@ function Dashboard({ spec }) {
 |---------|-------------|
 | `@json-render/core` | Schemas, catalogs, AI prompts, dynamic props, SpecStream utilities |
 | `@json-render/react` | React renderer, contexts, hooks |
+| `@json-render/vue` | Vue 3 renderer, composables, providers |
 | `@json-render/shadcn` | 36 pre-built shadcn/ui components (Radix UI + Tailwind CSS) |
 | `@json-render/react-native` | React Native renderer with standard mobile components |
 | `@json-render/remotion` | Remotion video renderer, timeline schema |
@@ -117,6 +121,7 @@ function Dashboard({ spec }) {
 | `@json-render/redux` | Redux / Redux Toolkit adapter for `StateStore` |
 | `@json-render/zustand` | Zustand adapter for `StateStore` |
 | `@json-render/jotai` | Jotai adapter for `StateStore` |
+| `@json-render/xstate-store` | XState Store (atom) adapter for `StateStore` |
 
 ## Renderers
 
@@ -148,6 +153,26 @@ const { registry } = defineRegistry(catalog, { components });
 <Renderer spec={spec} registry={registry} />
 ```
 
+### Vue (UI)
+
+```typescript
+import { h } from "vue";
+import { defineRegistry, Renderer } from "@json-render/vue";
+import { schema } from "@json-render/vue/schema";
+
+const { registry } = defineRegistry(catalog, {
+  components: {
+    Card: ({ props, children }) =>
+      h("div", { class: "card" }, [h("h3", null, props.title), children]),
+    Button: ({ props, emit }) =>
+      h("button", { onClick: () => emit("press") }, props.label),
+  },
+});
+
+// In your Vue component template:
+// <Renderer :spec="spec" :registry="registry" />
+```
+
 ### shadcn/ui (Web)
 
 ```tsx

apps/web/app/(main)/docs/api/vue/page.mdx

@@ -0,0 +1,246 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/vue")
+
+# @json-render/vue
+
+Vue 3 components, providers, and composables.
+
+## Providers
+
+### StateProvider
+
+```vue
+<StateProvider :initial-state="object" :on-state-change="fn">
+  <!-- children -->
+</StateProvider>
+```
+
+| Prop | Type | Description |
+|------|------|-------------|
+| `store` | `StateStore` | External store (controlled mode). When provided, `initialState` and `onStateChange` are ignored. |
+| `initialState` | `Record<string, unknown>` | Initial state model (uncontrolled mode). |
+| `onStateChange` | `(changes: Array<{ path: string; value: unknown }>) => void` | Callback when state changes (uncontrolled mode). Called once per `set` or `update` with all changed entries. |
+
+#### External Store (Controlled Mode)
+
+Pass a `StateStore` to bypass the internal state and wire json-render to any state management library:
+
+```typescript
+import { createStateStore, type StateStore } from "@json-render/vue";
+
+const store = createStateStore({ count: 0 });
+```
+
+```vue
+<StateProvider :store="store">
+  <!-- children -->
+</StateProvider>
+```
+
+```typescript
+// Mutate from anywhere — Vue re-renders automatically:
+store.set("/count", 1);
+```
+
+### ActionProvider
+
+```vue
+<ActionProvider :handlers="Record<string, ActionHandler>" :navigate="fn">
+  <!-- children -->
+</ActionProvider>
+
+// type ActionHandler = (params: Record<string, unknown>) => void | Promise<void>;
+```
+
+### VisibilityProvider
+
+```vue
+<VisibilityProvider>
+  <!-- children -->
+</VisibilityProvider>
+```
+
+`VisibilityProvider` reads state from the parent `StateProvider` automatically. Conditions in specs use the `VisibilityCondition` format with `$state` paths (e.g. `{ "$state": "/path" }`, `{ "$state": "/path", "eq": value }`). See [visibility](/docs/visibility) for the full syntax.
+
+### ValidationProvider
+
+```vue
+<ValidationProvider :custom-functions="Record<string, ValidationFunction>">
+  <!-- children -->
+</ValidationProvider>
+
+// type ValidationFunction = (value: unknown, args?: object) => boolean | Promise<boolean>;
+```
+
+## defineRegistry
+
+Create a type-safe component registry from a catalog. Components receive `props`, `children`, `emit`, `on`, and `loading` with catalog-inferred types.
+
+When the catalog declares actions, the `actions` field is required. When the catalog has no actions (e.g. `actions: {}`), the field is optional. When passing stubs, any `async () => {}` is sufficient.
+
+```typescript
+import { h } from "vue";
+import { defineRegistry } from "@json-render/vue";
+
+const { registry } = defineRegistry(catalog, {
+  components: {
+    Card: ({ props, children }) =>
+      h("div", { class: "card" }, [h("h3", null, props.title), children]),
+    Button: ({ props, emit }) =>
+      h("button", { onClick: () => emit("press") }, props.label),
+  },
+  // Required when catalog declares actions:
+  actions: {
+    submit: async (params) => { /* ... */ },
+  },
+});
+
+// Pass to <Renderer>
+// <Renderer :spec="spec" :registry="registry" />
+```
+
+## Components
+
+### Renderer
+
+```vue
+<Renderer
+  :spec="Spec"           // The UI spec to render
+  :registry="Registry"   // Component registry (from defineRegistry)
+  :loading="boolean"     // Optional loading state
+  :fallback="Component"  // Optional fallback for unknown types
+/>
+```
+
+### Component Props (via defineRegistry)
+
+```typescript
+import type { VNode } from "vue";
+
+interface ComponentContext<P> {
+  props: P;                          // Typed props from catalog
+  children?: VNode | VNode[];        // Rendered children (for container components)
+  emit: (event: string) => void;     // Emit a named event (always defined)
+  on: (event: string) => EventHandle; // Get event handle with metadata
+  loading?: boolean;
+  bindings?: Record<string, string>; // State paths from $bindState/$bindItem expressions
+}
+
+interface EventHandle {
+  emit: () => void;              // Fire the event
+  shouldPreventDefault: boolean; // Whether any binding requested preventDefault
+  bound: boolean;                // Whether any handler is bound
+}
+```
+
+Use `emit("press")` for simple event firing. Use `on("click")` when you need metadata like `shouldPreventDefault`:
+
+```typescript
+Link: ({ props, on }) => {
+  const click = on("click");
+  return h("a", {
+    href: props.href,
+    onClick: (e: MouseEvent) => {
+      if (click.shouldPreventDefault) e.preventDefault();
+      click.emit();
+    },
+  }, props.label);
+},
+```
+
+### BaseComponentProps
+
+Catalog-agnostic base type for building reusable component libraries that are not tied to a specific catalog:
+
+```typescript
+import type { BaseComponentProps } from "@json-render/vue";
+
+const Card = ({ props, children }: BaseComponentProps<{ title?: string }>) =>
+  h("div", null, [props.title, children]);
+```
+
+## Composables
+
+### useStateStore
+
+```typescript
+const {
+  state,   // ShallowRef<StateModel> — access with state.value
+  get,     // (path: string) => unknown
+  set,     // (path: string, value: unknown) => void
+  update,  // (updates: Record<string, unknown>) => void
+} = useStateStore();
+```
+
+> **Note:** `state` is a `ShallowRef<StateModel>`, not a plain object. Use `state.value` to read the current state. This differs from the React renderer.
+
+### useStateValue
+
+```typescript
+const value = useStateValue(path: string); // ComputedRef<T | undefined>
+```
+
+Returns a `ComputedRef` that automatically updates when the state at `path` changes. Use `.value` to access the current value.
+
+### useStateBinding (deprecated)
+
+> **Deprecated.** Use `$bindState` expressions with `bindings` prop instead.
+
+```typescript
+const [value, setValue] = useStateBinding(path: string);
+// value: ComputedRef<T | undefined>
+// setValue: (value: T) => void
+```
+
+### useActions
+
+```typescript
+const { execute } = useActions();
+// execute(binding: ActionBinding) => Promise<void>
+```
+
+### useAction
+
+```typescript
+const { execute, isLoading } = useAction(binding: ActionBinding);
+// execute: () => Promise<void>
+// isLoading: ComputedRef<boolean>
+```
+
+### useIsVisible
+
+```typescript
+const isVisible = useIsVisible(condition?: VisibilityCondition);
+```
+
+### useFieldValidation
+
+```typescript
+const {
+  state,     // ComputedRef<FieldValidationState>
+  validate,  // () => ValidationResult
+  touch,     // () => void
+  clear,     // () => void
+  errors,    // ComputedRef<string[]>
+  isValid,   // ComputedRef<boolean>
+} = useFieldValidation(path: string, config?: ValidationConfig);
+```
+
+`ValidationConfig` is `{ checks?: ValidationCheck[], validateOn?: 'change' | 'blur' | 'submit' }`.
+
+## Differences from `@json-render/react`
+
+| API | React | Vue | Note |
+|-----|-------|-----|------|
+| `useStateStore().state` | `StateModel` (plain object) | `ShallowRef<StateModel>` | Vue reactivity; use `state.value` |
+| `useStateValue()` | `T \| undefined` | `ComputedRef<T \| undefined>` | Vue reactivity; use `.value` |
+| `useStateBinding()` | `[T \| undefined, setter]` | `[ComputedRef<T \| undefined>, setter]` | Vue reactivity; use `value.value` |
+| `useAction().isLoading` | `boolean` | `ComputedRef<boolean>` | Vue reactivity; use `.value` |
+| `useFieldValidation().state` | `FieldValidationState` | `ComputedRef<FieldValidationState>` | Vue reactivity; use `.value` |
+| `useFieldValidation().errors` | `string[]` | `ComputedRef<string[]>` | Vue reactivity; use `.value` |
+| `useFieldValidation().isValid` | `boolean` | `ComputedRef<boolean>` | Vue reactivity; use `.value` |
+| `VisibilityContextValue.ctx` | `CoreVisibilityContext` | `ComputedRef<CoreVisibilityContext>` | Vue reactivity; use `ctx.value` |
+| `children` type | `React.ReactNode` | `VNode \| VNode[]` | Platform-specific |
+| `useBoundProp` | exported | exported | Same API; returns `[value, setValue]` |
+| `VisibilityProviderProps` | exported | not exported (no props) | Vue uses slot, no prop needed |
+| Streaming hooks | `useUIStream`, `useChatUI` | `useUIStream`, `useChatUI` | Same API; returns Vue `Ref` values |

apps/web/app/(main)/docs/computed-values/page.mdx

@@ -0,0 +1,119 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/computed-values")
+
+# Computed Values
+
+Derive dynamic prop values using registered functions or string templates.
+
+## `$template` — String Interpolation
+
+Use `{ "$template": "..." }` to embed state values into a string. References use `${/path}` syntax where the path is a JSON Pointer:
+
+```json
+{
+  "type": "Text",
+  "props": {
+    "text": { "$template": "Hello, ${/user/name}! You have ${/inbox/count} messages." }
+  },
+  "children": []
+}
+```
+
+If state is `{ "user": { "name": "Alice" }, "inbox": { "count": 3 } }`, the text renders as "Hello, Alice! You have 3 messages."
+
+Missing paths resolve to an empty string.
+
+## `$computed` — Registered Functions
+
+Use `{ "$computed": "<name>", "args": { ... } }` to call a named function registered in your catalog. Each arg can be a literal value or any prop expression (`$state`, `$item`, `$cond`, etc.):
+
+```json
+{
+  "type": "Text",
+  "props": {
+    "text": {
+      "$computed": "fullName",
+      "args": {
+        "first": { "$state": "/form/firstName" },
+        "last": { "$state": "/form/lastName" }
+      }
+    }
+  },
+  "children": []
+}
+```
+
+### Registering Functions
+
+Functions are registered in the catalog and provided at runtime.
+
+**Catalog definition (for AI prompt generation):**
+
+```typescript
+import { defineCatalog } from '@json-render/core';
+import { schema } from '@json-render/react/schema';
+
+const catalog = defineCatalog(schema, {
+  components: { /* ... */ },
+  functions: {
+    fullName: {
+      description: 'Combines first and last name into a full name',
+    },
+    formatCurrency: {
+      description: 'Formats a number as currency',
+    },
+  },
+});
+```
+
+**Runtime implementation:**
+
+```tsx
+import { JSONUIProvider } from '@json-render/react';
+
+const functions = {
+  fullName: (args) => `${args.first ?? ''} ${args.last ?? ''}`.trim(),
+  formatCurrency: (args) => {
+    const value = Number(args.value ?? 0);
+    return new Intl.NumberFormat('en-US', {
+      style: 'currency',
+      currency: (args.currency as string) ?? 'USD',
+    }).format(value);
+  },
+};
+
+<JSONUIProvider registry={registry} functions={functions}>
+  <Renderer spec={spec} registry={registry} />
+</JSONUIProvider>
+```
+
+### Using with `createRenderer`
+
+```tsx
+const MyRenderer = createRenderer(catalog, components);
+
+<MyRenderer
+  spec={spec}
+  functions={functions}
+/>
+```
+
+## Combining Expressions
+
+`$computed` args can use any expression type. This example computes a total from repeat item fields:
+
+```json
+{
+  "$computed": "lineTotal",
+  "args": {
+    "price": { "$item": "price" },
+    "quantity": { "$item": "quantity" }
+  }
+}
+```
+
+## Next
+
+- [Watchers](/docs/watchers) — react to state changes with cascading actions
+- [Data Binding](/docs/data-binding) — all expression types
+- [Validation](/docs/validation) — validate form inputs

apps/web/app/(main)/docs/data-binding/page.mdx

@@ -213,6 +213,22 @@ Use `$cond` / `$then` / `$else` to pick a prop value based on a condition:
 
 The condition uses the same [visibility](/docs/visibility) expression format.
 
+## Template Strings
+
+Use `{ "$template": "..." }` to interpolate state values into a string using `${/path}` syntax:
+
+```json
+{
+  "type": "Text",
+  "props": {
+    "text": { "$template": "Welcome back, ${/user/name}!" }
+  },
+  "children": []
+}
+```
+
+See [Computed Values](/docs/computed-values) for details on `$template` and `$computed` expressions.
+
 ## Quick Reference
 
 <div className="my-6 overflow-x-auto">
@@ -255,6 +271,16 @@ The condition uses the same [visibility](/docs/visibility) expression format.
         <td><code>{'{ "$bindItem": "field" }'}</code></td>
         <td>Form components inside repeat</td>
       </tr>
+      <tr>
+        <td><code>{"$template"}</code></td>
+        <td><code>{'{ "$template": "Hello, ${/name}!" }'}</code></td>
+        <td>Anywhere (string props)</td>
+      </tr>
+      <tr>
+        <td><code>{"$computed"}</code></td>
+        <td><code>{'{ "$computed": "fn", "args": { ... } }'}</code></td>
+        <td>Anywhere (requires registered function)</td>
+      </tr>
     </tbody>
   </table>
 </div>

apps/web/app/(main)/docs/installation/page.mdx

@@ -9,6 +9,18 @@ Install the core package plus your renderer of choice.
 
 <PackageInstall packages="@json-render/core @json-render/react" />
 
+Peer dependencies: `react ^19.0.0` and `zod ^4.0.0`.
+
+<PackageInstall packages="react zod" />
+
+## For Vue
+
+<PackageInstall packages="@json-render/core @json-render/vue" />
+
+Peer dependencies: `vue ^3.5.0` and `zod ^4.0.0`.
+
+<PackageInstall packages="vue zod" />
+
 ## For React UI with shadcn/ui
 
 Pre-built components for fast prototyping and production use:
@@ -37,15 +49,6 @@ If you want to wire json-render to an existing state management library instead
 
 See the [Data Binding](/docs/data-binding#external-store-controlled-mode) guide for usage.
 
-## Peer Dependencies
-
-json-render requires the following peer dependencies:
-
-- `react` ^19.0.0
-- `zod` ^4.0.0
-
-<PackageInstall packages="react zod" />
-
 ## For AI Integration
 
 To use json-render with AI models, you'll also need the Vercel AI SDK:

apps/web/app/(main)/docs/validation/page.mdx

@@ -11,11 +11,18 @@ json-render includes common validation functions:
 
 - `required` — Value must be non-empty
 - `email` — Valid email format
-- `minLength` — Minimum string length
-- `maxLength` — Maximum string length
-- `pattern` — Match a regex pattern
-- `min` — Minimum numeric value
-- `max` — Maximum numeric value
+- `minLength` — Minimum string length (args: `{ "min": N }`)
+- `maxLength` — Maximum string length (args: `{ "max": N }`)
+- `pattern` — Match a regex pattern (args: `{ "pattern": "regex" }`)
+- `min` — Minimum numeric value (args: `{ "min": N }`)
+- `max` — Maximum numeric value (args: `{ "max": N }`)
+- `numeric` — Value must be a number
+- `url` — Valid URL format
+- `matches` — Must equal another field (args: `{ "other": { "$state": "/path" } }`)
+- `equalTo` — Alias for matches (args: `{ "other": { "$state": "/path" } }`)
+- `lessThan` — Value must be less than another field (args: `{ "other": { "$state": "/path" } }`)
+- `greaterThan` — Value must be greater than another field (args: `{ "other": { "$state": "/path" } }`)
+- `requiredIf` — Required only when another field is truthy (args: `{ "field": { "$state": "/path" } }`)
 
 ## Using Validation in JSON
 
@@ -143,14 +150,114 @@ function TextField({ props, bindings }) {
 
 See the [@json-render/react API reference](/docs/api/react) for full `ValidationProvider` and `useFieldValidation` documentation.
 
+## Cross-Field Validation
+
+Validation args support `{ "$state": "/path" }` references to compare against other fields. This enables cross-field rules like "confirm password must match password":
+
+```json
+{
+  "type": "Input",
+  "props": {
+    "label": "Confirm Password",
+    "value": { "$bindState": "/form/confirmPassword" },
+    "checks": [
+      { "type": "required", "message": "Please confirm your password" },
+      {
+        "type": "matches",
+        "args": { "other": { "$state": "/form/password" } },
+        "message": "Passwords must match"
+      }
+    ]
+  }
+}
+```
+
+Other cross-field examples:
+
+```json
+{
+  "checks": [
+    {
+      "type": "greaterThan",
+      "args": { "other": { "$state": "/form/startDate" } },
+      "message": "End date must be after start date"
+    }
+  ]
+}
+```
+
+```json
+{
+  "checks": [
+    {
+      "type": "requiredIf",
+      "args": { "field": { "$state": "/form/enableNotifications" } },
+      "message": "Email is required when notifications are enabled"
+    }
+  ]
+}
+```
+
+## Conditional Validation
+
+Use the `enabled` field in the validation config to only run checks when a condition is met:
+
+```json
+{
+  "type": "Input",
+  "props": {
+    "label": "Company Name",
+    "value": { "$bindState": "/form/company" },
+    "checks": [
+      { "type": "required", "message": "Company name is required" }
+    ]
+  }
+}
+```
+
+In the component implementation, you can pass `enabled` to `useFieldValidation`:
+
+```typescript
+useFieldValidation(bindings?.value ?? "", {
+  checks: props.checks ?? [],
+  enabled: { "$state": "/form/accountType", eq: "business" },
+});
+```
+
+This only validates the company name when the account type is "business".
+
 ## Validation Timing
 
 Control when validation runs with `validateOn`:
 
 - `change` — Validate on every input change
-- `blur` — Validate when field loses focus
+- `blur` — Validate when field loses focus (default for Input, Textarea)
 - `submit` — Validate only on form submission
 
+## Form-Level Validation
+
+Use the built-in `validateForm` action to validate all registered fields at once. This is useful for a "Submit" button that should validate the entire form before proceeding:
+
+```json
+{
+  "type": "Button",
+  "props": { "label": "Submit" },
+  "on": {
+    "press": [
+      { "action": "validateForm", "params": { "statePath": "/formResult" } },
+      { "action": "submitForm" }
+    ]
+  },
+  "children": []
+}
+```
+
+The `validateForm` action runs `validateAll()` and writes `{ valid: boolean }` to the specified state path (defaults to `/formValidation`). Your submit handler can then check `{ "$state": "/formResult/valid" }` to decide whether to proceed.
+
+> **Note:** Actions in a list execute sequentially, but `submitForm` does not automatically gate on validation. Guard submission with a `$cond` visibility condition on the button or check `{ "$state": "/formResult/valid" }` inside your action handler to skip submission when the form is invalid.
+
 ## Next
 
-Learn about [generation modes](/docs/generation-modes).
+- [Computed Values](/docs/computed-values) — derive dynamic prop values
+- [Watchers](/docs/watchers) — react to state changes
+- [Generation Modes](/docs/generation-modes) — how AI generates specs

apps/web/app/(main)/docs/watchers/page.mdx

@@ -0,0 +1,150 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/watchers")
+
+# Watchers
+
+React to state changes by triggering actions when watched paths update.
+
+## The `watch` Field
+
+Elements can have an optional `watch` field that maps state paths to action bindings. When the value at a watched path changes, the bound actions fire automatically.
+
+`watch` is a **top-level field** on the element (sibling of `type`, `props`, `children`) — not inside `props`.
+
+```json
+{
+  "type": "Select",
+  "props": {
+    "label": "Country",
+    "value": { "$bindState": "/form/country" },
+    "options": ["US", "Canada", "UK"]
+  },
+  "watch": {
+    "/form/country": {
+      "action": "loadCities",
+      "params": { "country": { "$state": "/form/country" } }
+    }
+  },
+  "children": []
+}
+```
+
+When the user selects a different country, the `loadCities` action fires with the new country value. The action handler can fetch city data and update state, causing a dependent city Select to re-render with new options.
+
+## Cascading Selects
+
+A common pattern is cascading dropdowns where selecting a value in one field loads options for another:
+
+```json
+{
+  "root": "form",
+  "elements": {
+    "form": {
+      "type": "Stack",
+      "props": { "direction": "vertical", "gap": "md" },
+      "children": ["country-select", "city-select"]
+    },
+    "country-select": {
+      "type": "Select",
+      "props": {
+        "label": "Country",
+        "value": { "$bindState": "/form/country" },
+        "options": ["US", "Canada", "UK"]
+      },
+      "watch": {
+        "/form/country": [
+          { "action": "loadCities", "params": { "country": { "$state": "/form/country" } } },
+          { "action": "setState", "params": { "statePath": "/form/city", "value": "" } }
+        ]
+      },
+      "children": []
+    },
+    "city-select": {
+      "type": "Select",
+      "props": {
+        "label": "City",
+        "value": { "$bindState": "/form/city" },
+        "options": { "$state": "/availableCities" },
+        "placeholder": "Select a city"
+      },
+      "children": []
+    }
+  },
+  "state": {
+    "form": { "country": "", "city": "" },
+    "availableCities": []
+  }
+}
+```
+
+The watcher on `country-select` fires two actions when the country changes:
+1. `loadCities` — fetches and writes city options to `/availableCities`
+2. `setState` — resets the city selection
+
+The city Select reads its options from `{ "$state": "/availableCities" }`, so it automatically updates when the data is loaded.
+
+### Action Handler
+
+```typescript
+const handlers = {
+  loadCities: async (params) => {
+    const cities = await fetchCities(params.country);
+    // setState is called by the runtime to write the result
+    return cities;
+  },
+};
+```
+
+Or with `defineRegistry`:
+
+```typescript
+const { registry, handlers } = defineRegistry(catalog, {
+  components: { /* ... */ },
+  actions: {
+    loadCities: async (params, setState) => {
+      const response = await fetch(`/api/cities?country=${params.country}`);
+      const cities = await response.json();
+      setState('/availableCities', cities);
+    },
+  },
+});
+```
+
+## Multiple Watchers
+
+An element can watch multiple state paths. Each path maps to one or more action bindings:
+
+```json
+{
+  "watch": {
+    "/form/startDate": { "action": "validateDateRange" },
+    "/form/endDate": { "action": "validateDateRange" },
+    "/form/quantity": [
+      { "action": "recalculateTotal" },
+      { "action": "checkInventory", "params": { "qty": { "$state": "/form/quantity" } } }
+    ]
+  }
+}
+```
+
+## Behavior
+
+- Watchers only fire on **value changes**, not on the initial render
+- Comparison is by reference (`===`), not deep equality
+- Action params support the same expressions as event bindings (`$state`, `$item`, `$index`)
+- Multiple action bindings on the same path execute sequentially
+
+## When to Use `watch` vs `on`
+
+| Mechanism | Trigger | Use Case |
+|-----------|---------|----------|
+| `on` | User interaction (press, change, blur) | Button clicks, input changes, form submissions |
+| `watch` | State value change (any source) | Cascading data, derived state, cross-field sync |
+
+Use `on` when reacting to direct user actions. Use `watch` when a state change (from any source — user input, action handler, or external store update) should trigger side effects.
+
+## Next
+
+- [Data Binding](/docs/data-binding) — connect elements to state
+- [Computed Values](/docs/computed-values) — derive prop values
+- [Visibility](/docs/visibility) — conditionally show or hide elements

apps/web/lib/docs-navigation.ts

@@ -27,7 +27,9 @@ export const docsNavigation: NavSection[] = [
       { title: "Schemas", href: "/docs/schemas" },
       { title: "Catalog", href: "/docs/catalog" },
       { title: "Data Binding", href: "/docs/data-binding" },
+      { title: "Computed Values", href: "/docs/computed-values" },
       { title: "Visibility", href: "/docs/visibility" },
+      { title: "Watchers", href: "/docs/watchers" },
       { title: "Validation", href: "/docs/validation" },
     ],
   },
@@ -67,6 +69,16 @@ export const docsNavigation: NavSection[] = [
         href: "https://github.com/vercel-labs/json-render/tree/main/examples/remotion",
         external: true,
       },
+      {
+        title: "Vue",
+        href: "https://github.com/vercel-labs/json-render/tree/main/examples/vue",
+        external: true,
+      },
+      {
+        title: "Renders with Vite (Vue / React)",
+        href: "https://github.com/vercel-labs/json-render/tree/main/examples/vite-renderers",
+        external: true,
+      },
     ],
   },
   {
@@ -95,6 +107,7 @@ export const docsNavigation: NavSection[] = [
       { title: "@json-render/shadcn", href: "/docs/api/shadcn" },
       { title: "@json-render/react-native", href: "/docs/api/react-native" },
       { title: "@json-render/remotion", href: "/docs/api/remotion" },
+      { title: "@json-render/vue", href: "/docs/api/vue" },
       { title: "@json-render/codegen", href: "/docs/api/codegen" },
     ],
   },

apps/web/lib/page-titles.ts

@@ -38,6 +38,7 @@ export const PAGE_TITLES: Record<string, string> = {
   // API references
   "docs/api/core": "@json-render/core API",
   "docs/api/react": "@json-render/react API",
+  "docs/api/vue": "@json-render/vue API",
   "docs/api/react-pdf": "@json-render/react-pdf API",
   "docs/api/react-native": "@json-render/react-native API",
   "docs/api/codegen": "@json-render/codegen API",

examples/no-ai/app/page.tsx

@@ -2,33 +2,31 @@
 
 import { useState, useEffect, useCallback, type ReactNode } from "react";
 import ConfettiExplosion from "react-confetti-explosion";
-import {
-  Renderer,
-  StateProvider,
-  VisibilityProvider,
-  ActionProvider,
-  ValidationProvider,
-} from "@json-render/react";
+import { JSONUIProvider, Renderer } from "@json-render/react";
 import type { Spec } from "@json-render/core";
-import { registry, actionHandlers, onConfetti } from "@/lib/render/registry";
+import {
+  registry,
+  actionHandlers,
+  computedFunctions,
+  onConfetti,
+} from "@/lib/render/registry";
 import { examples } from "@/lib/examples";
 
 function SpecRenderer({ spec }: { spec: Spec }): ReactNode {
   return (
-    <StateProvider initialState={spec.state ?? {}}>
-      <VisibilityProvider>
-        <ActionProvider handlers={actionHandlers}>
-          <ValidationProvider>
-            <Renderer spec={spec} registry={registry} />
-          </ValidationProvider>
-        </ActionProvider>
-      </VisibilityProvider>
-    </StateProvider>
+    <JSONUIProvider
+      registry={registry}
+      initialState={spec.state ?? {}}
+      handlers={actionHandlers}
+      functions={computedFunctions}
+    >
+      <Renderer spec={spec} registry={registry} />
+    </JSONUIProvider>
   );
 }
 
 export default function Page() {
-  const [selectedIndex] = useState(0);
+  const [selectedIndex, setSelectedIndex] = useState(0);
   const selected = examples[selectedIndex]!;
   const [confettiKey, setConfettiKey] = useState(0);
   const [confettiActive, setConfettiActive] = useState(false);
@@ -41,30 +39,50 @@ export default function Page() {
   useEffect(() => onConfetti(fireConfetti), [fireConfetti]);
 
   return (
-    <div className="h-screen flex items-center justify-center bg-muted/30">
-      <div
-        className="relative bg-background border rounded-lg shadow-sm"
-        style={{ width: 960, height: 1080 }}
-      >
-        {confettiActive && (
-          <div className="absolute inset-0 flex items-center justify-center pointer-events-none">
-            <ConfettiExplosion
-              key={confettiKey}
-              portal={false}
-              force={0.8}
-              duration={3500}
-              particleCount={400}
-              particleSize={8}
-              colors={["#00F0FF", "#7B61FF", "#FF3DFF", "#00FF94", "#FFE14D"]}
-              width={1600}
-              height="200vh"
-              zIndex={1}
-              onComplete={() => setConfettiActive(false)}
-            />
+    <div className="h-screen flex flex-col bg-muted/30">
+      {/* Example selector */}
+      <nav className="flex gap-1 p-3 overflow-x-auto border-b bg-background shrink-0">
+        {examples.map((ex, i) => (
+          <button
+            key={ex.name}
+            onClick={() => setSelectedIndex(i)}
+            className={`px-3 py-1.5 text-sm rounded-md whitespace-nowrap transition-colors ${
+              i === selectedIndex
+                ? "bg-primary text-primary-foreground"
+                : "hover:bg-muted"
+            }`}
+          >
+            {ex.name}
+          </button>
+        ))}
+      </nav>
+
+      {/* Render area */}
+      <div className="flex-1 flex items-start justify-center overflow-auto p-6">
+        <div className="relative bg-background border rounded-lg shadow-sm w-full max-w-[960px]">
+          {confettiActive && (
+            <div className="absolute inset-0 flex items-center justify-center pointer-events-none">
+              <ConfettiExplosion
+                key={confettiKey}
+                portal={false}
+                force={0.8}
+                duration={3500}
+                particleCount={400}
+                particleSize={8}
+                colors={["#00F0FF", "#7B61FF", "#FF3DFF", "#00FF94", "#FFE14D"]}
+                width={1600}
+                height="200vh"
+                zIndex={1}
+                onComplete={() => setConfettiActive(false)}
+              />
+            </div>
+          )}
+          <div className="p-6 relative z-10">
+            <p className="text-xs text-muted-foreground mb-4">
+              {selected.description}
+            </p>
+            <SpecRenderer key={selectedIndex} spec={selected.spec} />
           </div>
-        )}
-        <div className="h-full overflow-auto p-6 flex items-center justify-center relative z-10">
-          <SpecRenderer key={selectedIndex} spec={selected.spec} />
         </div>
       </div>
     </div>

examples/no-ai/lib/examples.ts

@@ -508,4 +508,353 @@ export const examples: Example[] = [
       },
     },
   },
+
+  // =========================================================================
+  // Advanced: Registration form with cross-field validation & $template
+  // =========================================================================
+  {
+    name: "Registration Form",
+    description:
+      "Cross-field validation, $template preview, and validateForm action",
+    spec: {
+      root: "card",
+      state: {
+        form: {
+          name: "",
+          email: "",
+          password: "",
+          confirmPassword: "",
+          accountType: "personal",
+          company: "",
+        },
+        result: null,
+      },
+      elements: {
+        card: {
+          type: "Card",
+          props: {
+            title: "Create Account",
+            description: "Fill out the form below to register",
+            maxWidth: "md",
+            centered: null,
+          },
+          children: ["formStack"],
+        },
+        formStack: {
+          type: "Stack",
+          props: {
+            direction: "vertical",
+            gap: "md",
+            align: null,
+            justify: null,
+          },
+          children: [
+            "preview",
+            "sep0",
+            "nameInput",
+            "emailInput",
+            "passwordInput",
+            "confirmInput",
+            "sep1",
+            "accountTypeRadio",
+            "companyInput",
+            "sep2",
+            "actions",
+            "statusText",
+          ],
+        },
+
+        // $template live preview
+        preview: {
+          type: "Text",
+          props: {
+            text: {
+              $template: "Welcome, ${/form/name}! Your email: ${/form/email}",
+            },
+            variant: "muted",
+          },
+          visible: { $state: "/form/name", neq: "" },
+          children: [],
+        },
+        sep0: { type: "Separator", props: { orientation: null }, children: [] },
+
+        nameInput: {
+          type: "Input",
+          props: {
+            label: "Full Name",
+            name: "name",
+            type: "text",
+            placeholder: "Jane Doe",
+            value: { $bindState: "/form/name" },
+            checks: [
+              { type: "required", message: "Name is required" },
+              {
+                type: "minLength",
+                args: { min: 2 },
+                message: "Name must be at least 2 characters",
+              },
+            ],
+            validateOn: "blur",
+          },
+          children: [],
+        },
+        emailInput: {
+          type: "Input",
+          props: {
+            label: "Email",
+            name: "email",
+            type: "email",
+            placeholder: "jane@example.com",
+            value: { $bindState: "/form/email" },
+            checks: [
+              { type: "required", message: "Email is required" },
+              { type: "email", message: "Enter a valid email address" },
+            ],
+            validateOn: "blur",
+          },
+          children: [],
+        },
+        passwordInput: {
+          type: "Input",
+          props: {
+            label: "Password",
+            name: "password",
+            type: "password",
+            placeholder: "At least 8 characters",
+            value: { $bindState: "/form/password" },
+            checks: [
+              { type: "required", message: "Password is required" },
+              {
+                type: "minLength",
+                args: { min: 8 },
+                message: "Password must be at least 8 characters",
+              },
+            ],
+            validateOn: "blur",
+          },
+          children: [],
+        },
+        confirmInput: {
+          type: "Input",
+          props: {
+            label: "Confirm Password",
+            name: "confirmPassword",
+            type: "password",
+            placeholder: "Re-enter your password",
+            value: { $bindState: "/form/confirmPassword" },
+            checks: [
+              { type: "required", message: "Please confirm your password" },
+              {
+                type: "matches",
+                args: { other: { $state: "/form/password" } },
+                message: "Passwords must match",
+              },
+            ],
+            validateOn: "blur",
+          },
+          children: [],
+        },
+        sep1: { type: "Separator", props: { orientation: null }, children: [] },
+
+        accountTypeRadio: {
+          type: "Radio",
+          props: {
+            label: "Account Type",
+            name: "accountType",
+            options: ["personal", "business"],
+            value: { $bindState: "/form/accountType" },
+            checks: null,
+            validateOn: null,
+          },
+          children: [],
+        },
+        companyInput: {
+          type: "Input",
+          props: {
+            label: "Company Name",
+            name: "company",
+            type: "text",
+            placeholder: "Acme Inc.",
+            value: { $bindState: "/form/company" },
+            checks: [
+              {
+                type: "requiredIf",
+                args: { field: { $state: "/form/accountType" } },
+                message: "Company name is required for business accounts",
+              },
+            ],
+            validateOn: "blur",
+          },
+          visible: { $state: "/form/accountType", eq: "business" },
+          children: [],
+        },
+        sep2: { type: "Separator", props: { orientation: null }, children: [] },
+
+        actions: {
+          type: "Stack",
+          props: {
+            direction: "horizontal",
+            gap: "sm",
+            align: null,
+            justify: "end",
+          },
+          children: ["submitBtn"],
+        },
+        submitBtn: {
+          type: "Button",
+          props: { label: "Register", variant: "primary", disabled: null },
+          on: {
+            press: [
+              {
+                action: "validateForm",
+                params: { statePath: "/result" },
+              },
+            ],
+          },
+          children: [],
+        },
+
+        // Validation result
+        statusText: {
+          type: "Alert",
+          props: {
+            title: "Validation Result",
+            message: {
+              $cond: { $state: "/result/valid", eq: true },
+              $then: "All fields are valid -- ready to submit!",
+              $else: "Please fix the errors above before submitting.",
+            },
+            type: {
+              $cond: { $state: "/result/valid", eq: true },
+              $then: "success",
+              $else: "error",
+            },
+          },
+          visible: { $state: "/result", neq: null },
+          children: [],
+        },
+      },
+    },
+  },
+
+  // =========================================================================
+  // Advanced: Cascading selects with watchers & $computed
+  // =========================================================================
+  {
+    name: "Cascading Selects",
+    description:
+      "Watchers reset dependent fields, $computed derives display values",
+    spec: {
+      root: "card",
+      state: {
+        form: { country: "", city: "" },
+        availableCities: [],
+      },
+      elements: {
+        card: {
+          type: "Card",
+          props: {
+            title: "Shipping Address",
+            description: "Select your country to load available cities",
+            maxWidth: "md",
+            centered: null,
+          },
+          children: ["formStack"],
+        },
+        formStack: {
+          type: "Stack",
+          props: {
+            direction: "vertical",
+            gap: "md",
+            align: null,
+            justify: null,
+          },
+          children: [
+            "countrySelect",
+            "citySelect",
+            "sep",
+            "addressPreview",
+            "templatePreview",
+          ],
+        },
+
+        countrySelect: {
+          type: "Select",
+          props: {
+            label: "Country",
+            name: "country",
+            options: ["US", "Canada", "UK", "Germany", "Japan"],
+            placeholder: "Choose a country",
+            value: { $bindState: "/form/country" },
+            checks: [{ type: "required", message: "Country is required" }],
+            validateOn: "change",
+          },
+          watch: {
+            "/form/country": [
+              {
+                action: "setState",
+                params: {
+                  statePath: "/availableCities",
+                  value: {
+                    $computed: "citiesForCountry",
+                    args: { country: { $state: "/form/country" } },
+                  },
+                },
+              },
+              {
+                action: "setState",
+                params: { statePath: "/form/city", value: "" },
+              },
+            ],
+          },
+          children: [],
+        },
+
+        citySelect: {
+          type: "Select",
+          props: {
+            label: "City",
+            name: "city",
+            options: { $state: "/availableCities" },
+            placeholder: "Select a city",
+            value: { $bindState: "/form/city" },
+            checks: [{ type: "required", message: "City is required" }],
+            validateOn: "change",
+          },
+          children: [],
+        },
+        sep: { type: "Separator", props: { orientation: null }, children: [] },
+
+        // $computed formatted address
+        addressPreview: {
+          type: "Heading",
+          props: {
+            text: {
+              $computed: "formatAddress",
+              args: {
+                city: { $state: "/form/city" },
+                country: { $state: "/form/country" },
+              },
+            },
+            level: "h3",
+          },
+          children: [],
+        },
+
+        // $template string interpolation
+        templatePreview: {
+          type: "Text",
+          props: {
+            text: {
+              $template:
+                "Shipping to: ${/form/city} in ${/form/country}. Cities available: ${/availableCities}",
+            },
+            variant: "muted",
+          },
+          visible: { $state: "/form/country", neq: "" },
+          children: [],
+        },
+      },
+    },
+  },
 ];

examples/no-ai/lib/render/catalog.ts

@@ -13,4 +13,13 @@ export const catalog = defineCatalog(schema, {
       description: "Fire confetti",
     },
   },
+  functions: {
+    formatAddress: {
+      description:
+        "Formats country and city into a single address string like 'City, Country'",
+    },
+    citiesForCountry: {
+      description: "Returns an array of city names for the given country code",
+    },
+  },
 });

examples/no-ai/lib/render/registry.tsx

@@ -1,6 +1,7 @@
 "use client";
 
 import { defineRegistry } from "@json-render/react";
+import type { ComputedFunction } from "@json-render/core";
 import { shadcnComponents } from "@json-render/shadcn";
 import { catalog } from "./catalog";
 
@@ -13,6 +14,14 @@ export function onConfetti(cb: () => void) {
   };
 }
 
+const cityData: Record<string, string[]> = {
+  US: ["New York", "Los Angeles", "Chicago", "Houston", "Phoenix"],
+  Canada: ["Toronto", "Vancouver", "Montreal", "Calgary", "Ottawa"],
+  UK: ["London", "Manchester", "Birmingham", "Edinburgh", "Bristol"],
+  Germany: ["Berlin", "Munich", "Hamburg", "Frankfurt", "Cologne"],
+  Japan: ["Tokyo", "Osaka", "Kyoto", "Yokohama", "Sapporo"],
+};
+
 export const { registry } = defineRegistry(catalog, {
   components: {
     ...shadcnComponents,
@@ -24,6 +33,23 @@ export const { registry } = defineRegistry(catalog, {
   },
 });
 
-export const actionHandlers: Record<string, () => void> = {
+export const actionHandlers: Record<
+  string,
+  (params: Record<string, unknown>) => void
+> = {
   confetti: () => confettiListener?.(),
 };
+
+export const computedFunctions: Record<string, ComputedFunction> = {
+  formatAddress: (args) => {
+    const city = (args.city as string) ?? "";
+    const country = (args.country as string) ?? "";
+    if (!city && !country) return "No location selected";
+    if (!city) return country;
+    return `${city}, ${country}`;
+  },
+  citiesForCountry: (args) => {
+    const country = (args.country as string) ?? "";
+    return cityData[country] ?? [];
+  },
+};

examples/vite-renderers/index.html

@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>@json-render multi-renderer demo</title>
+    <style>
+      * {
+        box-sizing: border-box;
+        margin: 0;
+        padding: 0;
+      }
+
+      body {
+        font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+        background: #f3f4f6;
+        min-height: 100vh;
+      }
+
+      #renderer-root {
+        max-width: 640px;
+        margin: 0 auto;
+        padding: 24px;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="renderer-root"></div>
+    <script type="module" src="/src/main.ts"></script>
+  </body>
+</html>

examples/vite-renderers/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "vite-renderers",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "portless vite-renderers.json-render vite",
+    "build": "vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "@json-render/core": "workspace:*",
+    "@json-render/react": "workspace:*",
+    "@json-render/vue": "workspace:*",
+    "react": "^19.2.4",
+    "react-dom": "^19.2.4",
+    "vue": "^3.5.29",
+    "zod": "^4.3.6"
+  },
+  "devDependencies": {
+    "@types/react": "^19.2.14",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react": "^5.1.4",
+    "@vitejs/plugin-vue": "^6.0.4",
+    "typescript": "^5.9.3",
+    "vite": "^7.3.1"
+  }
+}

examples/vite-renderers/src/main.ts

@@ -0,0 +1,30 @@
+import "./shared/styles.css";
+import { demoSpec } from "./spec";
+
+type Renderer = "vue" | "react";
+
+const container = document.getElementById("renderer-root") as HTMLElement;
+
+let unmountCurrent: (() => void) | null = null;
+
+async function switchTo(renderer: Renderer) {
+  unmountCurrent?.();
+  container.innerHTML = "";
+  if (renderer === "vue") {
+    const mod = await import("./vue/mount.ts");
+    mod.mount(container, renderer, demoSpec);
+    unmountCurrent = mod.unmount;
+  } else {
+    const mod = await import("./react/mount.tsx");
+    mod.mount(container, renderer, demoSpec);
+    unmountCurrent = mod.unmount;
+  }
+}
+
+// The RendererTabs component (rendered by JSON renderer) dispatches this event
+document.addEventListener("switch-renderer", (e: Event) => {
+  switchTo((e as CustomEvent<string>).detail as Renderer);
+});
+
+// Default: Vue
+switchTo("vue");

examples/vite-renderers/src/react/App.tsx

@@ -0,0 +1,51 @@
+import { useMemo } from "react";
+import type { Spec } from "@json-render/core";
+import {
+  StateProvider,
+  ActionProvider,
+  VisibilityProvider,
+  ValidationProvider,
+  Renderer,
+  defineRegistry,
+  useStateStore,
+} from "@json-render/react";
+import { catalog } from "./catalog";
+import { components } from "./registry";
+import { actionStubs, makeHandlers } from "../shared/handlers";
+
+const { registry } = defineRegistry(catalog, {
+  components,
+  actions: actionStubs,
+});
+
+function DemoRenderer({ spec }: { spec: Spec }) {
+  const { get, set } = useStateStore();
+  const handlers = useMemo(() => makeHandlers(get, set), [get, set]);
+  return (
+    <ActionProvider handlers={handlers}>
+      <VisibilityProvider>
+        <ValidationProvider>
+          <Renderer spec={spec} registry={registry} />
+        </ValidationProvider>
+      </VisibilityProvider>
+    </ActionProvider>
+  );
+}
+
+export default function App({
+  initialRenderer = "vue",
+  spec,
+}: {
+  initialRenderer?: string;
+  spec: Spec;
+}) {
+  return (
+    <div className={`renderer-${initialRenderer}`}>
+      <StateProvider
+        initialState={{ ...spec.state, renderer: initialRenderer }}
+      >
+        <DemoRenderer spec={spec} />
+      </StateProvider>
+    </div>
+  );
+}

examples/vite-renderers/src/react/catalog.ts

@@ -0,0 +1,5 @@
+import { schema } from "@json-render/react/schema";
+import { catalogDef } from "../shared/catalog-def";
+
+export const catalog = schema.createCatalog(catalogDef);
+export type AppCatalog = typeof catalog;

examples/vite-renderers/src/react/mount.tsx

@@ -0,0 +1,15 @@
+import { createRoot, type Root } from "react-dom/client";
+import type { Spec } from "@json-render/core";
+import App from "./App";
+
+let root: Root | null = null;
+
+export function mount(container: HTMLElement, renderer: string, spec: Spec) {
+  root = createRoot(container);
+  root.render(<App initialRenderer={renderer} spec={spec} />);
+}
+
+export function unmount() {
+  root?.unmount();
+  root = null;
+}

examples/vite-renderers/src/react/registry.tsx

@@ -0,0 +1,155 @@
+import type { Components } from "@json-render/react";
+import type { AppCatalog } from "./catalog";
+
+export const components: Components<AppCatalog> = {
+  Stack: ({ props, children }) => (
+    <div
+      className={[
+        "json-render-stack",
+        props.direction === "horizontal" && "json-render-stack--horizontal",
+        props.align && `json-render-stack--align-${props.align}`,
+      ]
+        .filter(Boolean)
+        .join(" ")}
+      style={{
+        gap: props.gap ? `${props.gap}px` : undefined,
+        padding: props.padding ? `${props.padding}px` : undefined,
+      }}
+    >
+      {children}
+    </div>
+  ),
+
+  Card: ({ props, children }) => (
+    <div className="json-render-card">
+      {props.title && (
+        <div className="json-render-card-title-wrap">
+          <h2 className="json-render-card-title">{props.title}</h2>
+        </div>
+      )}
+      {props.subtitle && (
+        <p className="json-render-card-subtitle">{props.subtitle}</p>
+      )}
+      {children}
+    </div>
+  ),
+
+  Text: ({ props }) => (
+    <span
+      className={[
+        "json-render-text",
+        props.size && props.size !== "md" && `json-render-text--${props.size}`,
+        props.weight &&
+          props.weight !== "normal" &&
+          `json-render-text--${props.weight}`,
+      ]
+        .filter(Boolean)
+        .join(" ")}
+      style={props.color ? { color: props.color } : undefined}
+    >
+      {String(props.content ?? "")}
+    </span>
+  ),
+
+  Button: ({ props, emit }) => (
+    <button
+      disabled={props.disabled}
+      onClick={() => emit("press")}
+      className={[
+        "json-render-button",
+        props.variant && `json-render-button--${props.variant}`,
+      ]
+        .filter(Boolean)
+        .join(" ")}
+    >
+      {props.label}
+    </button>
+  ),
+
+  Badge: ({ props }) => (
+    <span
+      className="json-render-badge"
+      style={
+        props.color
+          ? {
+              backgroundColor: `${props.color}20`,
+              color: props.color,
+              borderColor: `${props.color}40`,
+            }
+          : undefined
+      }
+    >
+      {props.label}
+    </span>
+  ),
+
+  ListItem: ({ props, emit }) => (
+    <div
+      onClick={() => emit("press")}
+      className={[
+        "json-render-list-item",
+        props.completed && "json-render-list-item--done",
+      ]
+        .filter(Boolean)
+        .join(" ")}
+    >
+      <div
+        className={[
+          "json-render-list-item-check",
+          props.completed && "json-render-list-item-check--done",
+        ]
+          .filter(Boolean)
+          .join(" ")}
+      >
+        {props.completed ? "✓" : ""}
+      </div>
+      <span
+        className={[
+          "json-render-list-item-text",
+          props.completed && "json-render-list-item-text--done",
+        ]
+          .filter(Boolean)
+          .join(" ")}
+      >
+        {props.title}
+      </span>
+    </div>
+  ),
+
+  RendererBadge: ({ props }) => (
+    <span className="json-render-renderer-badge">
+      <span className="json-render-renderer-dot" />
+      {props.renderer === "vue" ? "Rendered with Vue" : "Rendered with React"}
+    </span>
+  ),
+
+  RendererTabs: ({ props, emit }) => (
+    <div className="json-render-renderer-tabs-wrapper">
+      <span className="json-render-renderer-tabs-label">Render</span>
+      <div className="json-render-renderer-tabs">
+        <button
+          onClick={() => emit("pressVue")}
+          className={[
+            "json-render-renderer-tab",
+            props.renderer === "vue" && "json-render-renderer-tab--active",
+          ]
+            .filter(Boolean)
+            .join(" ")}
+        >
+          Vue
+        </button>
+        <button
+          onClick={() => emit("pressReact")}
+          className={[
+            "json-render-renderer-tab",
+            props.renderer === "react" && "json-render-renderer-tab--active",
+          ]
+            .filter(Boolean)
+            .join(" ")}
+        >
+          React
+        </button>
+      </div>
+    </div>
+  ),
+};

examples/vite-renderers/src/shared/catalog-def.ts

@@ -0,0 +1,99 @@
+import { z } from "zod";
+
+/**
+ * Shared catalog definition — imported by both vue/catalog.ts and react/catalog.ts.
+ * Each renderer calls schema.createCatalog(catalogDef) with its own schema instance.
+ */
+export const catalogDef = {
+  components: {
+    Stack: {
+      props: z.object({
+        gap: z.number().optional(),
+        padding: z.number().optional(),
+        direction: z.enum(["vertical", "horizontal"]).optional(),
+        align: z.enum(["start", "center", "end"]).optional(),
+      }),
+      slots: ["default"],
+      description:
+        "Layout container that stacks children vertically or horizontally",
+    },
+    Card: {
+      props: z.object({
+        title: z.string().optional(),
+        subtitle: z.string().optional(),
+      }),
+      slots: ["default"],
+      description: "A card container with optional title and subtitle",
+    },
+    Text: {
+      props: z.object({
+        content: z.string(),
+        size: z.enum(["sm", "md", "lg", "xl"]).optional(),
+        weight: z.enum(["normal", "medium", "bold"]).optional(),
+        color: z.string().optional(),
+      }),
+      slots: [],
+      description: "Displays a text string",
+    },
+    Button: {
+      props: z.object({
+        label: z.string(),
+        variant: z.enum(["primary", "secondary", "danger"]).optional(),
+        disabled: z.boolean().optional(),
+      }),
+      slots: [],
+      description: "A clickable button that emits a 'press' event",
+    },
+    Badge: {
+      props: z.object({
+        label: z.string(),
+        color: z.string().optional(),
+      }),
+      slots: [],
+      description: "A small badge/tag label",
+    },
+    ListItem: {
+      props: z.object({
+        title: z.string(),
+        description: z.string().optional(),
+        completed: z.boolean().optional(),
+      }),
+      slots: [],
+      description: "A single item in a list",
+    },
+    RendererTabs: {
+      props: z.object({ renderer: z.string() }),
+      slots: [],
+      description:
+        "Segmented tab control for switching between Vue and React renderers",
+    },
+    RendererBadge: {
+      props: z.object({ renderer: z.string() }),
+      slots: [],
+      description: "Badge indicating which renderer is currently active",
+    },
+  },
+  actions: {
+    increment: {
+      params: z.object({}),
+      description: "Increment the counter by 1",
+    },
+    decrement: {
+      params: z.object({}),
+      description: "Decrement the counter by 1",
+    },
+    reset: { params: z.object({}), description: "Reset the counter to 0" },
+    toggleItem: {
+      params: z.object({ index: z.number() }),
+      description: "Toggle the completed state of a todo item",
+    },
+    switchToVue: {
+      params: z.object({}),
+      description: "Switch to the Vue renderer",
+    },
+    switchToReact: {
+      params: z.object({}),
+      description: "Switch to the React renderer",
+    },
+  },
+};

examples/vite-renderers/src/shared/handlers.ts

@@ -0,0 +1,50 @@
+type Get = (path: string) => unknown;
+type Set = (path: string, value: unknown) => void;
+
+/** Stub actions for defineRegistry (no-ops; real logic is in makeHandlers) */
+export const actionStubs = {
+  increment: async () => {},
+  decrement: async () => {},
+  reset: async () => {},
+  toggleItem: async () => {},
+  switchToVue: async () => {},
+  switchToReact: async () => {},
+};
+
+/** Creates action handlers that close over the state store's get/set */
+export function makeHandlers(get: Get, set: Set) {
+  return {
+    increment: async () => {
+      set("/count", Number(get("/count") || 0) + 1);
+    },
+    decrement: async () => {
+      set("/count", Math.max(0, Number(get("/count") || 0) - 1));
+    },
+    reset: async () => {
+      set("/count", 0);
+    },
+    toggleItem: async (params: Record<string, unknown>) => {
+      const index = params.index as number;
+      const todos = (
+        get("/todos") as Array<{
+          id: number;
+          title: string;
+          completed: boolean;
+        }>
+      ).slice();
+      const item = todos[index];
+      if (item) todos[index] = { ...item, completed: !item.completed };
+      set("/todos", todos);
+    },
+    switchToVue: async () => {
+      document.dispatchEvent(
+        new CustomEvent("switch-renderer", { detail: "vue" }),
+      );
+    },
+    switchToReact: async () => {
+      document.dispatchEvent(
+        new CustomEvent("switch-renderer", { detail: "react" }),
+      );
+    },
+  };
+}

examples/vite-renderers/src/shared/styles.css

@@ -0,0 +1,248 @@
+/* ---- Stack ---------------------------------------------------------------- */
+
+.json-render-stack {
+  display: flex;
+  flex-direction: column;
+  align-items: stretch;
+}
+
+.json-render-stack--horizontal {
+  flex-direction: row;
+  align-items: center;
+}
+
+.json-render-stack--align-start  { align-items: flex-start; }
+.json-render-stack--align-center { align-items: center; }
+.json-render-stack--align-end    { align-items: flex-end; }
+
+/* ---- Card ----------------------------------------------------------------- */
+
+.json-render-card {
+  background-color: white;
+  border-radius: 12px;
+  border: 1px solid #e5e7eb;
+  padding: 20px;
+  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.05);
+}
+
+.json-render-card-title-wrap {
+  margin-bottom: 4px;
+}
+
+.json-render-card-title {
+  font-size: 16px;
+  font-weight: 600;
+  color: #111827;
+  margin: 0;
+}
+
+.json-render-card-subtitle {
+  font-size: 13px;
+  color: #6b7280;
+  margin: 0 0 12px 0;
+}
+
+/* ---- Text ----------------------------------------------------------------- */
+
+.json-render-text {
+  font-size: 14px;
+  font-weight: 400;
+  color: #111827;
+}
+
+.json-render-text--sm { font-size: 12px; }
+.json-render-text--lg { font-size: 16px; }
+.json-render-text--xl { font-size: 24px; }
+
+.json-render-text--medium { font-weight: 500; }
+.json-render-text--bold   { font-weight: 700; }
+
+/* ---- Button --------------------------------------------------------------- */
+
+.json-render-button {
+  padding: 8px 16px;
+  border-radius: 8px;
+  border: none;
+  cursor: pointer;
+  font-weight: 500;
+  font-size: 14px;
+  transition: background 0.15s;
+  background-color: #3b82f6;
+  color: white;
+}
+
+.json-render-button:disabled {
+  cursor: not-allowed;
+  opacity: 0.5;
+}
+
+.json-render-button--primary {
+  background-color: #3b82f6;
+  color: white;
+}
+
+.json-render-button--secondary {
+  background-color: #f3f4f6;
+  color: #374151;
+}
+
+.json-render-button--danger {
+  background-color: #fee2e2;
+  color: #dc2626;
+}
+
+/* ---- Badge ---------------------------------------------------------------- */
+
+.json-render-badge {
+  display: inline-block;
+  padding: 4px 12px;
+  border-radius: 999px;
+  font-size: 13px;
+  font-weight: 500;
+  background-color: #e0f2fe;
+  color: #0369a1;
+  border: 1px solid #bae6fd;
+}
+
+/* ---- ListItem ------------------------------------------------------------- */
+
+.json-render-list-item {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  padding: 10px 12px;
+  border-radius: 8px;
+  cursor: pointer;
+  background-color: #f9fafb;
+  border: 1px solid #e5e7eb;
+}
+
+.json-render-list-item--done {
+  background-color: #f0fdf4;
+  border-color: #bbf7d0;
+}
+
+.json-render-list-item-check {
+  width: 18px;
+  height: 18px;
+  border-radius: 50%;
+  border: 2px solid #d1d5db;
+  background-color: transparent;
+  flex-shrink: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  font-size: 11px;
+  color: white;
+}
+
+.json-render-list-item-check--done {
+  border-color: #16a34a;
+  background-color: #16a34a;
+}
+
+.json-render-list-item-text {
+  font-size: 14px;
+  color: #111827;
+  text-decoration: none;
+}
+
+.json-render-list-item-text--done {
+  color: #6b7280;
+  text-decoration: line-through;
+}
+
+/* ---- RendererBadge -------------------------------------------------------- */
+
+.json-render-renderer-badge {
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+  padding: 10px 15px;
+  border-radius: 999px;
+  font-size: 12px;
+  font-weight: 500;
+  /* default colors; overridden by renderer parent class below */
+  background-color: #e0f2fe;
+  color: #0369a1;
+  border: 1px solid #bae6fd;
+}
+
+.json-render-renderer-dot {
+  width: 6px;
+  height: 6px;
+  border-radius: 50%;
+  display: inline-block;
+  /* background overridden by renderer parent class below */
+  background-color: #0369a1;
+}
+
+/* ---- RendererTabs --------------------------------------------------------- */
+
+.json-render-renderer-tabs-wrapper {
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+  margin-left: auto;
+}
+
+.json-render-renderer-tabs-label {
+  font-size: 13px;
+  color: #6b7280;
+  font-weight: 500;
+}
+
+.json-render-renderer-tabs {
+  display: inline-flex;
+  border-radius: 8px;
+  border: 1px solid #e5e7eb;
+  overflow: hidden;
+}
+
+.json-render-renderer-tab {
+  padding: 6px 16px;
+  border: none;
+  border-right: 0;
+  cursor: pointer;
+  font-size: 13px;
+  font-weight: 500;
+  background-color: white;
+  color: #374151;
+  transition: background 0.15s;
+}
+
+.json-render-renderer-tab:first-child {
+  border-right: 1px solid #e5e7eb;
+}
+
+/* ---- Renderer-specific overrides ----------------------------------------- */
+
+.renderer-vue .json-render-renderer-badge {
+  color: #42b883;
+  background-color: #42b88318;
+  border-color: #42b88340;
+}
+
+.renderer-vue .json-render-renderer-dot {
+  background-color: #42b883;
+}
+
+.renderer-vue .json-render-renderer-tab--active {
+  background-color: #42b883;
+  color: white;
+}
+
+.renderer-react .json-render-renderer-badge {
+  color: #149eca;
+  background-color: #149eca18;
+  border-color: #149eca40;
+}
+
+.renderer-react .json-render-renderer-dot {
+  background-color: #149eca;
+}
+
+.renderer-react .json-render-renderer-tab--active {
+  background-color: #149eca;
+  color: white;
+}

examples/vite-renderers/src/spec.ts

@@ -0,0 +1,126 @@
+import type { Spec } from "@json-render/core";
+
+export const demoSpec: Spec = {
+  root: "root",
+  state: {
+    renderer: "vue",
+    count: 0,
+    todos: [
+      { id: 1, title: "Learn JSON Render", completed: true },
+      {
+        id: 2,
+        title: "Try @json-render/vue or @json-render/react",
+        completed: false,
+      },
+      { id: 3, title: "Build something awesome", completed: false },
+    ],
+  },
+  elements: {
+    root: {
+      type: "Stack",
+      props: { gap: 24, padding: 24, direction: "vertical" },
+      children: [
+        "demo-title",
+        "renderer-tabs",
+        "renderer-badge",
+        "counter-card",
+        "milestone-badge",
+        "todos-card",
+      ],
+    },
+
+    "demo-title": {
+      type: "Text",
+      props: {
+        content: "@json-render multi-renderer demo",
+        size: "xl",
+        weight: "bold",
+      },
+    },
+    "renderer-badge": {
+      type: "RendererBadge",
+      props: { renderer: { $state: "/renderer" } },
+    },
+    "renderer-tabs": {
+      type: "RendererTabs",
+      props: { renderer: { $state: "/renderer" } },
+      on: {
+        pressVue: { action: "switchToVue" },
+        pressReact: { action: "switchToReact" },
+      },
+    },
+
+    // ---- Counter card ----
+    "counter-card": {
+      type: "Card",
+      props: {
+        title: "Counter",
+        subtitle: "Click the buttons to change the count",
+      },
+      children: ["counter-body"],
+    },
+    "counter-body": {
+      type: "Stack",
+      props: { gap: 12, direction: "horizontal", align: "center" },
+      children: [
+        "decrement-btn",
+        "counter-value",
+        "increment-btn",
+        "reset-btn",
+      ],
+    },
+    "decrement-btn": {
+      type: "Button",
+      props: { label: "−", variant: "secondary" },
+      on: { press: { action: "decrement" } },
+    },
+    "counter-value": {
+      type: "Text",
+      props: {
+        content: { $state: "/count" },
+        size: "xl",
+        weight: "bold",
+      },
+    },
+    "increment-btn": {
+      type: "Button",
+      props: { label: "+", variant: "primary" },
+      on: { press: { action: "increment" } },
+    },
+    "reset-btn": {
+      type: "Button",
+      props: { label: "Reset", variant: "danger" },
+      on: { press: { action: "reset" } },
+    },
+
+    // ---- Milestone badge (visible only when count >= 10) ----
+    "milestone-badge": {
+      type: "Badge",
+      props: { label: "Milestone reached: 10!", color: "#10b981" },
+      visible: { $state: "/count", gte: 10 },
+    },
+
+    // ---- Todos card ----
+    "todos-card": {
+      type: "Card",
+      props: { title: "Todo List", subtitle: "Your tasks" },
+      children: ["todos-list"],
+    },
+    "todos-list": {
+      type: "Stack",
+      props: { gap: 8, direction: "vertical" },
+      repeat: { statePath: "/todos", key: "id" },
+      children: ["todo-item"],
+    },
+    "todo-item": {
+      type: "ListItem",
+      props: {
+        title: { $item: "title" },
+        completed: { $item: "completed" },
+      },
+      on: {
+        press: { action: "toggleItem", params: { index: { $index: true } } },
+      },
+    },
+  },
+};

examples/vite-renderers/src/vue/App.vue

@@ -0,0 +1,19 @@
+<script setup lang="ts">
+import type { Spec } from "@json-render/core";
+import { StateProvider } from "@json-render/vue";
+import DemoRenderer from "./DemoRenderer.vue";
+
+const props = defineProps<{
+  initialRenderer?: string; spec: Spec }>();
+const initialState = {
+  ...props.spec.state,
+  renderer: props.initialRenderer ?? "vue" };
+</script>
+
+<template>
+  <div :class="`renderer-${props.initialRenderer ?? 'vue'}`">
+    <StateProvider :initial-state="initialState">
+      <DemoRenderer :spec="props.spec" />
+    </StateProvider>
+  </div>
+</template>

examples/vite-renderers/src/vue/DemoRenderer.vue

@@ -0,0 +1,25 @@
+<script setup lang="ts">
+import type { Spec } from "@json-render/core";
+import {
+  ActionProvider, ValidationProvider, VisibilityProvider,
+  Renderer, defineRegistry, useStateStore,
+} from "@json-render/vue";
+import { catalog } from "./catalog";
+import { components } from "./registry";
+import { actionStubs, makeHandlers } from "../shared/handlers";
+
+const props = defineProps<{ spec: Spec }>();
+const { get, set } = useStateStore();
+const { registry } = defineRegistry(catalog, { components, actions: actionStubs });
+const handlers = makeHandlers(get, set);
+</script>
+
+<template>
+  <ActionProvider :handlers="handlers">
+    <VisibilityProvider>
+      <ValidationProvider>
+        <Renderer :spec="props.spec" :registry="registry" />
+      </ValidationProvider>
+    </VisibilityProvider>
+  </ActionProvider>
+</template>

examples/vite-renderers/src/vue/catalog.ts

@@ -0,0 +1,5 @@
+import { schema } from "@json-render/vue/schema";
+import { catalogDef } from "../shared/catalog-def";
+
+export const catalog = schema.createCatalog(catalogDef);
+export type AppCatalog = typeof catalog;

examples/vite-renderers/src/vue/mount.ts

@@ -0,0 +1,15 @@
+import { createApp, type App } from "vue";
+import type { Spec } from "@json-render/core";
+import VueApp from "./App.vue";
+
+let app: App | null = null;
+
+export function mount(container: HTMLElement, renderer: string, spec: Spec) {
+  app = createApp(VueApp, { initialRenderer: renderer, spec });
+  app.mount(container);
+}
+
+export function unmount() {
+  app?.unmount();
+  app = null;
+}

examples/vite-renderers/src/vue/registry.ts

@@ -0,0 +1,166 @@
+import { h } from "vue";
+import type { Components } from "@json-render/vue";
+import type { AppCatalog } from "./catalog";
+
+export const components: Components<AppCatalog> = {
+  Stack: ({ props, children }) =>
+    h(
+      "div",
+      {
+        class: [
+          "json-render-stack",
+          props.direction === "horizontal" && "json-render-stack--horizontal",
+          props.align && `json-render-stack--align-${props.align}`,
+        ]
+          .filter(Boolean)
+          .join(" "),
+        style: {
+          gap: props.gap ? `${props.gap}px` : undefined,
+          padding: props.padding ? `${props.padding}px` : undefined,
+        },
+      },
+      children,
+    ),
+
+  Card: ({ props, children }) =>
+    h("div", { class: "json-render-card" }, [
+      props.title &&
+        h("div", { class: "json-render-card-title-wrap" }, [
+          h("h2", { class: "json-render-card-title" }, props.title),
+        ]),
+      props.subtitle &&
+        h("p", { class: "json-render-card-subtitle" }, props.subtitle),
+      children,
+    ]),
+
+  Text: ({ props }) =>
+    h(
+      "span",
+      {
+        class: [
+          "json-render-text",
+          props.size &&
+            props.size !== "md" &&
+            `json-render-text--${props.size}`,
+          props.weight &&
+            props.weight !== "normal" &&
+            `json-render-text--${props.weight}`,
+        ]
+          .filter(Boolean)
+          .join(" "),
+        style: props.color ? { color: props.color } : undefined,
+      },
+      String(props.content ?? ""),
+    ),
+
+  Button: ({ props, emit }) =>
+    h(
+      "button",
+      {
+        disabled: props.disabled,
+        onClick: () => emit("press"),
+        class: [
+          "json-render-button",
+          props.variant && `json-render-button--${props.variant}`,
+        ]
+          .filter(Boolean)
+          .join(" "),
+      },
+      props.label,
+    ),
+
+  Badge: ({ props }) =>
+    h(
+      "span",
+      {
+        class: "json-render-badge",
+        style: props.color
+          ? {
+              backgroundColor: `${props.color}20`,
+              color: props.color,
+              borderColor: `${props.color}40`,
+            }
+          : undefined,
+      },
+      props.label,
+    ),
+
+  ListItem: ({ props, emit }) =>
+    h(
+      "div",
+      {
+        onClick: () => emit("press"),
+        class: [
+          "json-render-list-item",
+          props.completed && "json-render-list-item--done",
+        ]
+          .filter(Boolean)
+          .join(" "),
+      },
+      [
+        h(
+          "div",
+          {
+            class: [
+              "json-render-list-item-check",
+              props.completed && "json-render-list-item-check--done",
+            ]
+              .filter(Boolean)
+              .join(" "),
+          },
+          props.completed ? "✓" : "",
+        ),
+        h(
+          "span",
+          {
+            class: [
+              "json-render-list-item-text",
+              props.completed && "json-render-list-item-text--done",
+            ]
+              .filter(Boolean)
+              .join(" "),
+          },
+          props.title,
+        ),
+      ],
+    ),
+
+  RendererBadge: ({ props }) =>
+    h("span", { class: "json-render-renderer-badge" }, [
+      h("span", { class: "json-render-renderer-dot" }),
+      props.renderer === "vue" ? "Rendered with Vue" : "Rendered with React",
+    ]),
+
+  RendererTabs: ({ props, emit }) =>
+    h("div", { class: "json-render-renderer-tabs-wrapper" }, [
+      h("span", { class: "json-render-renderer-tabs-label" }, "Render"),
+      h("div", { class: "json-render-renderer-tabs" }, [
+        h(
+          "button",
+          {
+            onClick: () => emit("pressVue"),
+            class: [
+              "json-render-renderer-tab",
+              props.renderer === "vue" && "json-render-renderer-tab--active",
+            ]
+              .filter(Boolean)
+              .join(" "),
+          },
+          "Vue",
+        ),
+        h(
+          "button",
+          {
+            onClick: () => emit("pressReact"),
+            class: [
+              "json-render-renderer-tab",
+              props.renderer === "react" && "json-render-renderer-tab--active",
+            ]
+              .filter(Boolean)
+              .join(" "),
+          },
+          "React",
+        ),
+      ]),
+    ]),
+};

examples/vite-renderers/tsconfig.json

@@ -0,0 +1,17 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "useDefineForClassFields": true,
+    "module": "ESNext",
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "skipLibCheck": true,
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "isolatedModules": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "jsx": "react-jsx",
+    "strict": true
+  },
+  "include": ["src/**/*.ts", "src/**/*.tsx", "src/**/*.vue"]
+}

examples/vite-renderers/vite.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from "vite";
+import vue from "@vitejs/plugin-vue";
+import react from "@vitejs/plugin-react";
+
+export default defineConfig({
+  plugins: [vue(), react({ include: /\.tsx$/ })],
+});

examples/vue/index.html

@@ -0,0 +1,26 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>json-render vue example</title>
+    <style>
+      * {
+        box-sizing: border-box;
+        margin: 0;
+        padding: 0;
+      }
+      body {
+        font-family:
+          -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
+        background: #f9fafb;
+        color: #111827;
+        min-height: 100vh;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="app"></div>
+    <script type="module" src="/src/main.ts"></script>
+  </body>
+</html>

examples/vue/package.json

@@ -0,0 +1,22 @@
+{
+  "name": "vue",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "portless vue.json-render vite",
+    "build": "vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "@json-render/core": "workspace:*",
+    "@json-render/vue": "workspace:*",
+    "vue": "^3.5.0",
+    "zod": "^4.3.6"
+  },
+  "devDependencies": {
+    "@vitejs/plugin-vue": "^6.0.4",
+    "typescript": "^5.9.3",
+    "vite": "^7.3.1",
+    "vue-tsc": "^3.2.5"
+  }
+}

examples/vue/src/App.vue

@@ -0,0 +1,14 @@
+<script setup lang="ts">
+import { StateProvider } from "@json-render/vue";
+import { demoSpec } from "./lib/spec";
+import DemoRenderer from "./DemoRenderer.vue";
+
+const initialState = demoSpec.state ?? {};
+</script>
+
+<template>
+  <!-- StateProvider sets up the reactive state store for the whole tree -->
+  <StateProvider :initial-state="initialState">
+    <DemoRenderer />
+  </StateProvider>
+</template>

examples/vue/src/DemoRenderer.vue

@@ -0,0 +1,68 @@
+<script setup lang="ts">
+import {
+  ActionProvider,
+  ValidationProvider,
+  VisibilityProvider,
+  Renderer,
+  defineRegistry,
+  useStateStore,
+} from "@json-render/vue";
+import { catalog } from "./lib/catalog";
+import { components } from "./lib/registry";
+import { demoSpec } from "./lib/spec";
+
+// Access the state store provided by the parent StateProvider
+const { get, set } = useStateStore();
+
+// Build registry — include stub actions to satisfy catalog types.
+// The actual logic runs in the handlers below, which have direct
+// access to the state store.
+const { registry } = defineRegistry(catalog, {
+  components,
+  actions: {
+    increment: async () => {},
+    decrement: async () => {},
+    reset: async () => {},
+    toggleItem: async () => {},
+  },
+});
+
+// Action handlers — close over the state store's get/set so they
+// can read and write state directly without needing an external store.
+const handlers = {
+  increment: async () => {
+    set("/count", Number(get("/count") || 0) + 1);
+  },
+  decrement: async () => {
+    set("/count", Math.max(0, Number(get("/count") || 0) - 1));
+  },
+  reset: async () => {
+    set("/count", 0);
+  },
+  toggleItem: async (params: Record<string, unknown>) => {
+    const index = params.index as number;
+    const todos = (
+      get("/todos") as Array<{
+        id: number;
+        title: string;
+        completed: boolean;
+      }>
+    ).slice();
+    const item = todos[index];
+    if (item) {
+      todos[index] = { ...item, completed: !item.completed };
+    }
+    set("/todos", todos);
+  },
+};
+</script>
+
+<template>
+  <ActionProvider :handlers="handlers">
+    <VisibilityProvider>
+      <ValidationProvider>
+        <Renderer :spec="demoSpec" :registry="registry" />
+      </ValidationProvider>
+    </VisibilityProvider>
+  </ActionProvider>
+</template>

examples/vue/src/lib/catalog.ts

@@ -0,0 +1,92 @@
+import { schema } from "@json-render/vue/schema";
+import { z } from "zod";
+
+export const catalog = schema.createCatalog({
+  components: {
+    Stack: {
+      props: z.object({
+        gap: z.number().optional(),
+        padding: z.number().optional(),
+        direction: z.enum(["vertical", "horizontal"]).optional(),
+        align: z.enum(["start", "center", "end"]).optional(),
+      }),
+      slots: ["default"],
+      description:
+        "Layout container that stacks children vertically or horizontally",
+    },
+    Card: {
+      props: z.object({
+        title: z.string().optional(),
+        subtitle: z.string().optional(),
+      }),
+      slots: ["default"],
+      description: "A card container with optional title and subtitle",
+    },
+    Text: {
+      props: z.object({
+        content: z.string(),
+        size: z.enum(["sm", "md", "lg", "xl"]).optional(),
+        weight: z.enum(["normal", "medium", "bold"]).optional(),
+        color: z.string().optional(),
+      }),
+      slots: [],
+      description: "Displays a text string",
+    },
+    Button: {
+      props: z.object({
+        label: z.string(),
+        variant: z.enum(["primary", "secondary", "danger"]).optional(),
+        disabled: z.boolean().optional(),
+      }),
+      slots: [],
+      description: "A clickable button that emits a 'press' event",
+    },
+    Badge: {
+      props: z.object({
+        label: z.string(),
+        color: z.string().optional(),
+      }),
+      slots: [],
+      description: "A small badge/tag label",
+    },
+    ListItem: {
+      props: z.object({
+        title: z.string(),
+        description: z.string().optional(),
+        completed: z.boolean().optional(),
+      }),
+      slots: [],
+      description: "A single item in a list",
+    },
+    Input: {
+      props: z.object({
+        value: z.string().optional(),
+        placeholder: z.string().optional(),
+      }),
+      slots: [],
+      description: "A text input field that supports two-way state binding",
+    },
+  },
+  actions: {
+    increment: {
+      params: z.object({}),
+      description: "Increment the counter by 1",
+    },
+    decrement: {
+      params: z.object({}),
+      description: "Decrement the counter by 1",
+    },
+    reset: {
+      params: z.object({}),
+      description: "Reset the counter to 0",
+    },
+    toggleItem: {
+      params: z.object({
+        index: z.number(),
+      }),
+      description: "Toggle the completed state of a todo item",
+    },
+  },
+});
+
+export type AppCatalog = typeof catalog;

examples/vue/src/lib/registry.ts

@@ -0,0 +1,213 @@
+import { h } from "vue";
+import type { Components } from "@json-render/vue";
+import { useBoundProp } from "@json-render/vue";
+import type { AppCatalog } from "./catalog";
+
+export const components: Components<AppCatalog> = {
+  Stack: ({ props, children }) => {
+    const isHorizontal = props.direction === "horizontal";
+    return h(
+      "div",
+      {
+        style: {
+          display: "flex",
+          flexDirection: isHorizontal ? "row" : "column",
+          gap: props.gap ? `${props.gap}px` : undefined,
+          padding: props.padding ? `${props.padding}px` : undefined,
+          alignItems: props.align ?? (isHorizontal ? "center" : "stretch"),
+        },
+      },
+      children,
+    );
+  },
+
+  Card: ({ props, children }) =>
+    h(
+      "div",
+      {
+        style: {
+          backgroundColor: "white",
+          borderRadius: "12px",
+          border: "1px solid #e5e7eb",
+          padding: "20px",
+          boxShadow: "0 1px 3px rgba(0,0,0,0.05)",
+        },
+      },
+      [
+        props.title &&
+          h("div", { style: { marginBottom: "4px" } }, [
+            h(
+              "h2",
+              {
+                style: {
+                  fontSize: "16px",
+                  fontWeight: "600",
+                  color: "#111827",
+                  margin: 0,
+                },
+              },
+              props.title,
+            ),
+          ]),
+        props.subtitle &&
+          h(
+            "p",
+            {
+              style: {
+                fontSize: "13px",
+                color: "#6b7280",
+                margin: "0 0 12px 0",
+              },
+            },
+            props.subtitle,
+          ),
+        children,
+      ],
+    ),
+
+  Text: ({ props }) => {
+    const sizeMap: Record<string, string> = {
+      sm: "12px",
+      md: "14px",
+      lg: "16px",
+      xl: "24px",
+    };
+    const weightMap: Record<string, string> = {
+      normal: "400",
+      medium: "500",
+      bold: "700",
+    };
+    return h(
+      "span",
+      {
+        style: {
+          fontSize: sizeMap[props.size ?? "md"] ?? "14px",
+          fontWeight: weightMap[props.weight ?? "normal"] ?? "400",
+          color: props.color ?? "#111827",
+        },
+      },
+      String(props.content ?? ""),
+    );
+  },
+
+  Button: ({ props, emit }) =>
+    h(
+      "button",
+      {
+        disabled: props.disabled,
+        onClick: () => emit("press"),
+        style: {
+          padding: "8px 16px",
+          borderRadius: "8px",
+          border: "none",
+          cursor: props.disabled ? "not-allowed" : "pointer",
+          fontWeight: "500",
+          fontSize: "14px",
+          transition: "background 0.15s",
+          opacity: props.disabled ? "0.5" : "1",
+          backgroundColor:
+            props.variant === "danger"
+              ? "#fee2e2"
+              : props.variant === "secondary"
+                ? "#f3f4f6"
+                : "#3b82f6",
+          color:
+            props.variant === "danger"
+              ? "#dc2626"
+              : props.variant === "secondary"
+                ? "#374151"
+                : "white",
+        },
+      },
+      props.label,
+    ),
+
+  Badge: ({ props }) =>
+    h(
+      "span",
+      {
+        style: {
+          display: "inline-block",
+          padding: "4px 12px",
+          borderRadius: "999px",
+          fontSize: "13px",
+          fontWeight: "500",
+          backgroundColor: props.color ? `${props.color}20` : "#e0f2fe",
+          color: props.color ?? "#0369a1",
+          border: `1px solid ${props.color ? `${props.color}40` : "#bae6fd"}`,
+        },
+      },
+      props.label,
+    ),
+
+  Input: ({ props, bindings }) => {
+    const [value, setValue] = useBoundProp<string>(
+      props.value as string | undefined,
+      bindings?.value,
+    );
+    return h("input", {
+      value: value ?? "",
+      placeholder: props.placeholder as string | undefined,
+      onInput: (e: Event) => setValue((e.target as HTMLInputElement).value),
+      style: {
+        padding: "8px 12px",
+        borderRadius: "8px",
+        border: "1px solid #d1d5db",
+        fontSize: "14px",
+        outline: "none",
+        width: "100%",
+        boxSizing: "border-box",
+      },
+    });
+  },
+
+  ListItem: ({ props, emit }) =>
+    h(
+      "div",
+      {
+        onClick: () => emit("press"),
+        style: {
+          display: "flex",
+          alignItems: "center",
+          gap: "12px",
+          padding: "10px 12px",
+          borderRadius: "8px",
+          cursor: "pointer",
+          backgroundColor: props.completed ? "#f0fdf4" : "#f9fafb",
+          border: `1px solid ${props.completed ? "#bbf7d0" : "#e5e7eb"}`,
+        },
+      },
+      [
+        h(
+          "div",
+          {
+            style: {
+              width: "18px",
+              height: "18px",
+              borderRadius: "50%",
+              border: `2px solid ${props.completed ? "#16a34a" : "#d1d5db"}`,
+              backgroundColor: props.completed ? "#16a34a" : "transparent",
+              flexShrink: "0",
+              display: "flex",
+              alignItems: "center",
+              justifyContent: "center",
+              fontSize: "11px",
+              color: "white",
+            },
+          },
+          props.completed ? "✓" : "",
+        ),
+        h(
+          "span",
+          {
+            style: {
+              fontSize: "14px",
+              color: props.completed ? "#6b7280" : "#111827",
+              textDecoration: props.completed ? "line-through" : "none",
+            },
+          },
+          props.title,
+        ),
+      ],
+    ),
+};

examples/vue/src/lib/spec.ts

@@ -0,0 +1,138 @@
+import type { Spec } from "@json-render/core";
+
+export const demoSpec: Spec = {
+  root: "root",
+  state: {
+    count: 0,
+    name: "",
+    todos: [
+      { id: 1, title: "Learn Vue 3", completed: true },
+      { id: 2, title: "Try @json-render/vue", completed: false },
+      { id: 3, title: "Build something awesome", completed: false },
+    ],
+  },
+  elements: {
+    root: {
+      type: "Stack",
+      props: { gap: 24, padding: 24, direction: "vertical" },
+      children: [
+        "header",
+        "counter-card",
+        "milestone-badge",
+        "todos-card",
+        "input-card",
+      ],
+    },
+    header: {
+      type: "Text",
+      props: {
+        content: "@json-render/vue demo",
+        size: "xl",
+        weight: "bold",
+      },
+    },
+
+    // ---- Counter card ----
+    "counter-card": {
+      type: "Card",
+      props: {
+        title: "Counter",
+        subtitle: "Click the buttons to change the count",
+      },
+      children: ["counter-body"],
+    },
+    "counter-body": {
+      type: "Stack",
+      props: { gap: 12, direction: "horizontal", align: "center" },
+      children: [
+        "decrement-btn",
+        "counter-value",
+        "increment-btn",
+        "reset-btn",
+      ],
+    },
+    "decrement-btn": {
+      type: "Button",
+      props: { label: "−", variant: "secondary" },
+      on: { press: { action: "decrement" } },
+    },
+    "counter-value": {
+      type: "Text",
+      props: {
+        content: { $state: "/count" },
+        size: "xl",
+        weight: "bold",
+      },
+    },
+    "increment-btn": {
+      type: "Button",
+      props: { label: "+", variant: "primary" },
+      on: { press: { action: "increment" } },
+    },
+    "reset-btn": {
+      type: "Button",
+      props: { label: "Reset", variant: "danger" },
+      on: { press: { action: "reset" } },
+    },
+
+    // ---- Milestone badge (visible only when count >= 10) ----
+    "milestone-badge": {
+      type: "Badge",
+      props: { label: "Milestone reached: 10!", color: "#10b981" },
+      visible: { $state: "/count", gte: 10 },
+    },
+
+    // ---- Todos card ----
+    "todos-card": {
+      type: "Card",
+      props: { title: "Todo List", subtitle: "Your tasks" },
+      children: ["todos-list"],
+    },
+    "todos-list": {
+      type: "Stack",
+      props: { gap: 8, direction: "vertical" },
+      repeat: { statePath: "/todos", key: "id" },
+      children: ["todo-item"],
+    },
+    "todo-item": {
+      type: "ListItem",
+      props: {
+        title: { $item: "title" },
+        completed: { $item: "completed" },
+      },
+      on: {
+        press: { action: "toggleItem", params: { index: { $index: true } } },
+      },
+    },
+
+    // ---- Bound Input card (useBoundProp demo) ----
+    "input-card": {
+      type: "Card",
+      props: {
+        title: "Bound Input",
+        subtitle: "Type to update state — the display text reacts in real time",
+      },
+      children: ["input-body"],
+    },
+    "input-body": {
+      type: "Stack",
+      props: { gap: 12, direction: "vertical" },
+      children: ["name-input", "name-display"],
+    },
+    "name-input": {
+      type: "Input",
+      props: {
+        value: { $bindState: "/name" },
+        placeholder: "Enter your name…",
+      },
+    },
+    "name-display": {
+      type: "Text",
+      props: {
+        content: { $state: "/name" },
+        size: "md",
+        color: "#6b7280",
+      },
+    },
+  },
+};

examples/vue/src/main.ts

@@ -0,0 +1,4 @@
+import { createApp } from "vue";
+import App from "./App.vue";
+
+createApp(App).mount("#app");

examples/vue/tsconfig.json

@@ -0,0 +1,17 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "useDefineForClassFields": true,
+    "module": "ESNext",
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "skipLibCheck": true,
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "isolatedModules": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "jsx": "preserve",
+    "strict": true
+  },
+  "include": ["src/**/*.ts", "src/**/*.tsx", "src/**/*.vue"]
+}

examples/vue/vite.config.ts

@@ -0,0 +1,6 @@
+import { defineConfig } from "vite";
+import vue from "@vitejs/plugin-vue";
+
+export default defineConfig({
+  plugins: [vue()],
+});

package.json

@@ -12,7 +12,7 @@
   },
   "scripts": {
     "build": "turbo run build",
-    "dev": "turbo run dev --concurrency 15",
+    "dev": "turbo run dev --concurrency 20",
     "lint": "turbo run lint",
     "format": "prettier --write \"**/*.{ts,tsx}\"",
     "type-check": "turbo run check-types",

packages/core/src/index.ts

@@ -72,7 +72,11 @@ export {
 } from "./visibility";
 
 // Prop Expressions
-export type { PropExpression, PropResolutionContext } from "./props";
+export type {
+  PropExpression,
+  PropResolutionContext,
+  ComputedFunction,
+} from "./props";
 
 export {
   resolvePropValue,

packages/core/src/props.test.ts

@@ -1,9 +1,11 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
 import {
   resolvePropValue,
   resolveElementProps,
   resolveBindings,
   resolveActionParam,
+  _resetWarnedComputedFns,
+  _resetWarnedTemplatePaths,
 } from "./props";
 import type { PropResolutionContext } from "./props";
 
@@ -498,3 +500,165 @@ describe("resolveActionParam", () => {
     expect(resolveActionParam(null, ctx)).toBeNull();
   });
 });
+
+// =============================================================================
+// $computed expressions
+// =============================================================================
+
+describe("$computed expressions", () => {
+  it("calls a registered function with resolved args", () => {
+    const ctx: PropResolutionContext = {
+      stateModel: { form: { firstName: "Jane", lastName: "Doe" } },
+      functions: {
+        fullName: (args) => `${args.first} ${args.last}`,
+      },
+    };
+    expect(
+      resolvePropValue(
+        {
+          $computed: "fullName",
+          args: {
+            first: { $state: "/form/firstName" },
+            last: { $state: "/form/lastName" },
+          },
+        },
+        ctx,
+      ),
+    ).toBe("Jane Doe");
+  });
+
+  it("calls function with no args", () => {
+    const ctx: PropResolutionContext = {
+      stateModel: {},
+      functions: {
+        timestamp: () => 1234567890,
+      },
+    };
+    expect(resolvePropValue({ $computed: "timestamp" }, ctx)).toBe(1234567890);
+  });
+
+  it("returns undefined for unknown function", () => {
+    const ctx: PropResolutionContext = {
+      stateModel: {},
+      functions: {},
+    };
+    expect(resolvePropValue({ $computed: "unknown" }, ctx)).toBeUndefined();
+  });
+
+  it("returns undefined when no functions in context", () => {
+    const ctx: PropResolutionContext = { stateModel: {} };
+    expect(resolvePropValue({ $computed: "any" }, ctx)).toBeUndefined();
+  });
+
+  it("deduplicates warnings for the same unknown function", () => {
+    const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    const ctx: PropResolutionContext = { stateModel: {}, functions: {} };
+    resolvePropValue({ $computed: "dedupTest" }, ctx);
+    resolvePropValue({ $computed: "dedupTest" }, ctx);
+    const calls = warnSpy.mock.calls.filter((c) =>
+      String(c[0]).includes("dedupTest"),
+    );
+    expect(calls).toHaveLength(1);
+    warnSpy.mockRestore();
+  });
+
+  it("resolves nested expressions in args", () => {
+    const ctx: PropResolutionContext = {
+      stateModel: { active: true, values: { a: 10, b: 20 } },
+      functions: {
+        conditionalSum: (args) => {
+          if (args.enabled) return (args.x as number) + (args.y as number);
+          return 0;
+        },
+      },
+    };
+    expect(
+      resolvePropValue(
+        {
+          $computed: "conditionalSum",
+          args: {
+            enabled: { $state: "/active" },
+            x: { $state: "/values/a" },
+            y: { $state: "/values/b" },
+          },
+        },
+        ctx,
+      ),
+    ).toBe(30);
+  });
+});
+
+// =============================================================================
+// $template expressions
+// =============================================================================
+
+describe("$template expressions", () => {
+  it("interpolates state values into a string", () => {
+    const ctx: PropResolutionContext = {
+      stateModel: { user: { name: "Alice" }, count: 3 },
+    };
+    expect(
+      resolvePropValue(
+        { $template: "Hello, ${/user/name}! You have ${/count} messages." },
+        ctx,
+      ),
+    ).toBe("Hello, Alice! You have 3 messages.");
+  });
+
+  it("replaces missing paths with empty string", () => {
+    const ctx: PropResolutionContext = { stateModel: {} };
+    expect(resolvePropValue({ $template: "Hi ${/name}!" }, ctx)).toBe("Hi !");
+  });
+
+  it("handles template with no interpolations", () => {
+    const ctx: PropResolutionContext = { stateModel: {} };
+    expect(resolvePropValue({ $template: "No variables here" }, ctx)).toBe(
+      "No variables here",
+    );
+  });
+
+  it("handles multiple references to the same path", () => {
+    const ctx: PropResolutionContext = {
+      stateModel: { x: "A" },
+    };
+    expect(resolvePropValue({ $template: "${/x} and ${/x}" }, ctx)).toBe(
+      "A and A",
+    );
+  });
+
+  it("converts non-string values to strings", () => {
+    const ctx: PropResolutionContext = {
+      stateModel: { num: 42, bool: true },
+    };
+    expect(resolvePropValue({ $template: "${/num} is ${/bool}" }, ctx)).toBe(
+      "42 is true",
+    );
+  });
+
+  it("warns when path does not start with /", () => {
+    _resetWarnedTemplatePaths();
+    const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    const ctx: PropResolutionContext = { stateModel: { name: "Bob" } };
+    const result = resolvePropValue({ $template: "Hi ${name}!" }, ctx);
+    expect(result).toBe("Hi Bob!");
+    expect(warnSpy).toHaveBeenCalledWith(
+      expect.stringContaining('$template path "name"'),
+    );
+    warnSpy.mockRestore();
+    _resetWarnedTemplatePaths();
+  });
+
+  it("deduplicates warnings for the same $template path", () => {
+    _resetWarnedTemplatePaths();
+    const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    const ctx: PropResolutionContext = { stateModel: { name: "Bob" } };
+    resolvePropValue({ $template: "Hi ${name}!" }, ctx);
+    resolvePropValue({ $template: "Hi ${name}!" }, ctx);
+    const calls = warnSpy.mock.calls.filter((c) =>
+      String(c[0]).includes('$template path "name"'),
+    );
+    expect(calls).toHaveLength(1);
+    warnSpy.mockRestore();
+    _resetWarnedTemplatePaths();
+  });
+});

packages/core/src/props.ts

@@ -22,6 +22,10 @@ import { evaluateVisibility, type VisibilityContext } from "./visibility";
  *    repeat item — resolves via `repeatBasePath + path` and exposes the
  *    absolute state path for write-back.
  * - `{ $cond, $then, $else }` conditionally picks a value
+ * - `{ $computed: string, args?: Record<string, PropExpression> }` calls a
+ *    registered function with resolved args and returns the result
+ * - `{ $template: string }` interpolates `${/path}` references in the
+ *    string with values from the state model
  * - Any other value is a literal (passthrough)
  */
 export type PropExpression<T = unknown> =
@@ -35,7 +39,15 @@ export type PropExpression<T = unknown> =
       $cond: VisibilityCondition;
       $then: PropExpression<T>;
       $else: PropExpression<T>;
-    };
+    }
+  | { $computed: string; args?: Record<string, unknown> }
+  | { $template: string };
+
+/**
+ * Function signature for `$computed` expressions.
+ * Receives a record of resolved argument values and returns a computed result.
+ */
+export type ComputedFunction = (args: Record<string, unknown>) => unknown;
 
 /**
  * Context for resolving prop expressions.
@@ -45,6 +57,8 @@ export type PropExpression<T = unknown> =
 export interface PropResolutionContext extends VisibilityContext {
   /** Absolute state path to the current repeat item (e.g. "/todos/0"). Set inside repeat scopes. */
   repeatBasePath?: string;
+  /** Named functions available for `$computed` expressions. */
+  functions?: Record<string, ComputedFunction>;
 }
 
 // =============================================================================
@@ -110,6 +124,47 @@ function isCondExpression(
   );
 }
 
+function isComputedExpression(
+  value: unknown,
+): value is { $computed: string; args?: Record<string, unknown> } {
+  return (
+    typeof value === "object" &&
+    value !== null &&
+    "$computed" in value &&
+    typeof (value as Record<string, unknown>).$computed === "string"
+  );
+}
+
+function isTemplateExpression(value: unknown): value is { $template: string } {
+  return (
+    typeof value === "object" &&
+    value !== null &&
+    "$template" in value &&
+    typeof (value as Record<string, unknown>).$template === "string"
+  );
+}
+
+// Module-level set to avoid spamming console.warn on every render for the same
+// unknown $computed function name. Once the set reaches WARNED_COMPUTED_MAX,
+// new names are no longer deduplicated (warnings still fire) but the set stops
+// growing, preventing unbounded memory use in long-lived processes (e.g. SSR).
+const WARNED_COMPUTED_MAX = 100;
+const warnedComputedFns = new Set<string>();
+
+/** @internal Test-only: clear the deduplication set for $computed warnings. */
+export function _resetWarnedComputedFns(): void {
+  warnedComputedFns.clear();
+}
+
+// Same deduplication pattern for $template paths that don't start with "/".
+const WARNED_TEMPLATE_MAX = 100;
+const warnedTemplatePaths = new Set<string>();
+
+/** @internal Test-only: clear the deduplication set for $template warnings. */
+export function _resetWarnedTemplatePaths(): void {
+  warnedTemplatePaths.clear();
+}
+
 // =============================================================================
 // Prop Expression Resolution
 // =============================================================================
@@ -193,6 +248,50 @@ export function resolvePropValue(
     return resolvePropValue(result ? value.$then : value.$else, ctx);
   }
 
+  // $computed: call a registered function with resolved args
+  if (isComputedExpression(value)) {
+    const fn = ctx.functions?.[value.$computed];
+    if (!fn) {
+      if (!warnedComputedFns.has(value.$computed)) {
+        if (warnedComputedFns.size < WARNED_COMPUTED_MAX) {
+          warnedComputedFns.add(value.$computed);
+        }
+        console.warn(`Unknown $computed function: "${value.$computed}"`);
+      }
+      return undefined;
+    }
+    const resolvedArgs: Record<string, unknown> = {};
+    if (value.args) {
+      for (const [key, arg] of Object.entries(value.args)) {
+        resolvedArgs[key] = resolvePropValue(arg, ctx);
+      }
+    }
+    return fn(resolvedArgs);
+  }
+
+  // $template: interpolate ${/path} references with state values
+  if (isTemplateExpression(value)) {
+    return value.$template.replace(
+      /\$\{([^}]+)\}/g,
+      (_match, rawPath: string) => {
+        let path = rawPath;
+        if (!path.startsWith("/")) {
+          if (!warnedTemplatePaths.has(path)) {
+            if (warnedTemplatePaths.size < WARNED_TEMPLATE_MAX) {
+              warnedTemplatePaths.add(path);
+            }
+            console.warn(
+              `$template path "${path}" should be a JSON Pointer starting with "/". Automatically resolving as "/${path}".`,
+            );
+          }
+          path = "/" + path;
+        }
+        const resolved = getByPath(ctx.stateModel, path);
+        return resolved != null ? String(resolved) : "";
+      },
+    );
+  }
+
   // Arrays: resolve each element
   if (Array.isArray(value)) {
     return value.map((item) => resolvePropValue(item, ctx));

packages/core/src/schema.ts

@@ -900,6 +900,31 @@ Note: state patches appear right after the elements that use them, so the UI fil
     "Use $bindState for form inputs (text fields, checkboxes, selects, sliders, etc.) and $state for read-only data display. Inside repeat scopes, use $bindItem for form inputs bound to the current item. Use dynamic props instead of duplicating elements with opposing visible conditions when only prop values differ.",
   );
   lines.push("");
+  lines.push(
+    '4. Template: `{ "$template": "Hello, ${/name}!" }` - interpolates `${/path}` references in the string with values from the state model.',
+  );
+  lines.push(
+    '   Example: `"label": { "$template": "Items: ${/cart/count} | Total: ${/cart/total}" }` renders "Items: 3 | Total: 42.00" when /cart/count is 3 and /cart/total is 42.00.',
+  );
+  lines.push("");
+
+  // $computed section — only emit when catalog defines functions
+  const catalogFunctions = (catalog.data as Record<string, unknown>).functions;
+  if (catalogFunctions && Object.keys(catalogFunctions).length > 0) {
+    lines.push(
+      '5. Computed: `{ "$computed": "<functionName>", "args": { "key": <expression> } }` - calls a registered function with resolved args and returns the result.',
+    );
+    lines.push(
+      '   Example: `"value": { "$computed": "fullName", "args": { "first": { "$state": "/form/firstName" }, "last": { "$state": "/form/lastName" } } }`',
+    );
+    lines.push("   Available functions:");
+    for (const name of Object.keys(
+      catalogFunctions as Record<string, unknown>,
+    )) {
+      lines.push(`   - ${name}`);
+    }
+    lines.push("");
+  }
 
   // Validation section — only emit when at least one component has a `checks` prop
   const hasChecksComponents = allComponents
@@ -930,7 +955,19 @@ Note: state patches appear right after the elements that use them, so the UI fil
     lines.push("  - numeric — value must be a number");
     lines.push("  - url — valid URL format");
     lines.push(
-      '  - matches — must equal another field (args: { "other": "value" })',
+      '  - matches — must equal another field (args: { "other": { "$state": "/path" } })',
+    );
+    lines.push(
+      '  - equalTo — alias for matches (args: { "other": { "$state": "/path" } })',
+    );
+    lines.push(
+      '  - lessThan — value must be less than another field (args: { "other": { "$state": "/path" } })',
+    );
+    lines.push(
+      '  - greaterThan — value must be greater than another field (args: { "other": { "$state": "/path" } })',
+    );
+    lines.push(
+      '  - requiredIf — required only when another field is truthy (args: { "field": { "$state": "/path" } })',
     );
     lines.push("");
     lines.push("Example:");
@@ -947,6 +984,33 @@ Note: state patches appear right after the elements that use them, so the UI fil
     lines.push("");
   }
 
+  // State watchers section — only emit when actions are available (watchers
+  // trigger actions, so the section is irrelevant without them).
+  if (hasCustomActions || hasBuiltInActions) {
+    lines.push("STATE WATCHERS:");
+    lines.push(
+      "Elements can have an optional `watch` field to react to state changes and trigger actions. The `watch` field is a top-level field on the element (sibling of type/props/children), NOT inside props.",
+    );
+    lines.push(
+      "Maps state paths (JSON Pointers) to action bindings. When the value at a watched path changes, the bound actions fire automatically.",
+    );
+    lines.push("");
+    lines.push(
+      "Example (cascading select — country changes trigger city loading):",
+    );
+    lines.push(
+      `  ${JSON.stringify({ type: "Select", props: { value: { $bindState: "/form/country" }, options: ["US", "Canada", "UK"] }, watch: { "/form/country": { action: "loadCities", params: { country: { $state: "/form/country" } } } }, children: [] })}`,
+    );
+    lines.push("");
+    lines.push(
+      "Use `watch` for cascading dependencies where changing one field should trigger side effects (loading data, resetting dependent fields, computing derived values).",
+    );
+    lines.push(
+      "IMPORTANT: `watch` is a top-level field on the element (sibling of type/props/children), NOT inside props. Watchers only fire when the value changes, not on initial render.",
+    );
+    lines.push("");
+  }
+
   // Rules
   lines.push("RULES:");
   const baseRules =

packages/core/src/spec-validator.test.ts

@@ -0,0 +1,250 @@
+import { describe, it, expect } from "vitest";
+import type { Spec } from "./types";
+import { validateSpec, autoFixSpec } from "./spec-validator";
+
+// =============================================================================
+// validateSpec
+// =============================================================================
+
+describe("validateSpec", () => {
+  it("returns valid for a correct spec", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: { type: "Stack", props: {}, children: ["child1"] },
+        child1: { type: "Text", props: { text: "hello" }, children: [] },
+      },
+    };
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(true);
+    expect(result.issues).toHaveLength(0);
+  });
+
+  it("detects missing root", () => {
+    const spec = {
+      root: "",
+      elements: { a: { type: "T", props: {}, children: [] } },
+    } as Spec;
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(false);
+    expect(result.issues.some((i) => i.code === "missing_root")).toBe(true);
+  });
+
+  it("detects root_not_found", () => {
+    const spec: Spec = {
+      root: "missing",
+      elements: { a: { type: "T", props: {}, children: [] } },
+    };
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(false);
+    expect(result.issues.some((i) => i.code === "root_not_found")).toBe(true);
+  });
+
+  it("detects empty spec", () => {
+    const spec: Spec = { root: "r", elements: {} };
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(false);
+    expect(result.issues.some((i) => i.code === "empty_spec")).toBe(true);
+  });
+
+  it("detects missing_child", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: { type: "Stack", props: {}, children: ["nonexistent"] },
+      },
+    };
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(false);
+    expect(result.issues.some((i) => i.code === "missing_child")).toBe(true);
+  });
+
+  it("detects visible_in_props", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Text",
+          props: { visible: { $state: "/show" } },
+          children: [],
+        },
+      },
+    };
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(false);
+    expect(result.issues.some((i) => i.code === "visible_in_props")).toBe(true);
+  });
+
+  it("detects on_in_props", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Button",
+          props: { on: { press: { action: "doSomething" } } },
+          children: [],
+        },
+      },
+    };
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(false);
+    expect(result.issues.some((i) => i.code === "on_in_props")).toBe(true);
+  });
+
+  it("detects repeat_in_props", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Stack",
+          props: { repeat: { statePath: "/items" } },
+          children: [],
+        },
+      },
+    };
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(false);
+    expect(result.issues.some((i) => i.code === "repeat_in_props")).toBe(true);
+  });
+
+  it("detects watch_in_props", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Select",
+          props: {
+            watch: {
+              "/form/country": { action: "loadCities" },
+            },
+          },
+          children: [],
+        },
+      },
+    };
+    const result = validateSpec(spec);
+    expect(result.valid).toBe(false);
+    const watchIssue = result.issues.find((i) => i.code === "watch_in_props");
+    expect(watchIssue).toBeDefined();
+    expect(watchIssue!.elementKey).toBe("root");
+  });
+
+  it("detects orphaned elements when checkOrphans is true", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: { type: "Stack", props: {}, children: [] },
+        orphan: { type: "Text", props: {}, children: [] },
+      },
+    };
+    const result = validateSpec(spec, { checkOrphans: true });
+    expect(result.valid).toBe(true);
+    expect(result.issues.some((i) => i.code === "orphaned_element")).toBe(true);
+  });
+});
+
+// =============================================================================
+// autoFixSpec
+// =============================================================================
+
+describe("autoFixSpec", () => {
+  it("moves visible from props to element level", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Text",
+          props: { text: "hi", visible: { $state: "/show" } },
+          children: [],
+        },
+      },
+    };
+    const { spec: fixed, fixes } = autoFixSpec(spec);
+    expect(
+      (fixed.elements.root.props as Record<string, unknown>).visible,
+    ).toBeUndefined();
+    expect(fixed.elements.root.visible).toEqual({ $state: "/show" });
+    expect(fixes.some((f) => f.includes("visible"))).toBe(true);
+  });
+
+  it("moves on from props to element level", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Button",
+          props: { label: "OK", on: { press: { action: "submit" } } },
+          children: [],
+        },
+      },
+    };
+    const { spec: fixed, fixes } = autoFixSpec(spec);
+    expect(
+      (fixed.elements.root.props as Record<string, unknown>).on,
+    ).toBeUndefined();
+    expect(fixed.elements.root.on).toEqual({ press: { action: "submit" } });
+    expect(fixes.some((f) => f.includes('"on"'))).toBe(true);
+  });
+
+  it("moves repeat from props to element level", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Stack",
+          props: { repeat: { statePath: "/items" } },
+          children: ["child"],
+        },
+        child: { type: "Text", props: {}, children: [] },
+      },
+    };
+    const { spec: fixed, fixes } = autoFixSpec(spec);
+    expect(
+      (fixed.elements.root.props as Record<string, unknown>).repeat,
+    ).toBeUndefined();
+    expect(fixed.elements.root.repeat).toEqual({ statePath: "/items" });
+    expect(fixes.some((f) => f.includes('"repeat"'))).toBe(true);
+  });
+
+  it("moves watch from props to element level", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Select",
+          props: {
+            label: "Country",
+            watch: {
+              "/form/country": { action: "loadCities" },
+            },
+          },
+          children: [],
+        },
+      },
+    };
+    const { spec: fixed, fixes } = autoFixSpec(spec);
+    expect(
+      (fixed.elements.root.props as Record<string, unknown>).watch,
+    ).toBeUndefined();
+    expect(fixed.elements.root.watch).toEqual({
+      "/form/country": { action: "loadCities" },
+    });
+    expect(fixes.some((f) => f.includes('"watch"'))).toBe(true);
+  });
+
+  it("returns no fixes for a correct spec", () => {
+    const spec: Spec = {
+      root: "root",
+      elements: {
+        root: {
+          type: "Stack",
+          props: { direction: "vertical" },
+          children: [],
+          watch: { "/x": { action: "y" } },
+        },
+      },
+    };
+    const { fixes } = autoFixSpec(spec);
+    expect(fixes).toHaveLength(0);
+  });
+});

packages/core/src/spec-validator.ts

@@ -28,7 +28,8 @@ export interface SpecIssue {
     | "orphaned_element"
     | "empty_spec"
     | "on_in_props"
-    | "repeat_in_props";
+    | "repeat_in_props"
+    | "watch_in_props";
 }
 
 /**
@@ -151,6 +152,16 @@ export function validateSpec(
         code: "repeat_in_props",
       });
     }
+
+    // 3e. `watch` inside props (should be a top-level field)
+    if (props && "watch" in props && props.watch !== undefined) {
+      issues.push({
+        severity: "error",
+        message: `Element "${key}" has "watch" inside "props". It should be a top-level field on the element (sibling of type/props/children).`,
+        elementKey: key,
+        code: "watch_in_props",
+      });
+    }
   }
 
   // 4. Orphaned elements (optional)
@@ -248,6 +259,21 @@ export function autoFixSpec(spec: Spec): {
       fixes.push(`Moved "repeat" from props to element level on "${key}".`);
     }
 
+    currentProps = fixed.props as Record<string, unknown> | undefined;
+    if (
+      currentProps &&
+      "watch" in currentProps &&
+      currentProps.watch !== undefined
+    ) {
+      const { watch, ...restProps } = currentProps;
+      fixed = {
+        ...fixed,
+        props: restProps,
+        watch: watch as UIElement["watch"],
+      };
+      fixes.push(`Moved "watch" from props to element level on "${key}".`);
+    }
+
     fixedElements[key] = fixed;
   }
 

packages/core/src/types.ts

@@ -69,6 +69,12 @@ export interface UIElement<
   on?: Record<string, ActionBinding | ActionBinding[]>;
   /** Repeat children once per item in a state array */
   repeat?: { statePath: string; key?: string };
+  /**
+   * State watchers — maps JSON Pointer state paths to action bindings.
+   * When the value at a watched path changes, the bound actions fire.
+   * Useful for cascading dependencies (e.g. country → city option loading).
+   */
+  watch?: Record<string, ActionBinding | ActionBinding[]>;
 }
 
 /**

packages/core/src/validation.test.ts

@@ -187,6 +187,226 @@ describe("builtInValidationFunctions", () => {
       ).toBe(false);
     });
   });
+
+  describe("equalTo", () => {
+    it("passes when values are equal", () => {
+      expect(builtInValidationFunctions.equalTo("abc", { other: "abc" })).toBe(
+        true,
+      );
+    });
+
+    it("fails when values differ", () => {
+      expect(builtInValidationFunctions.equalTo("abc", { other: "xyz" })).toBe(
+        false,
+      );
+    });
+  });
+
+  describe("lessThan", () => {
+    it("passes when value is less than other", () => {
+      expect(builtInValidationFunctions.lessThan(3, { other: 5 })).toBe(true);
+    });
+
+    it("fails when value equals other", () => {
+      expect(builtInValidationFunctions.lessThan(5, { other: 5 })).toBe(false);
+    });
+
+    it("fails when value is greater than other", () => {
+      expect(builtInValidationFunctions.lessThan(7, { other: 5 })).toBe(false);
+    });
+
+    it("coerces numeric string vs number", () => {
+      expect(builtInValidationFunctions.lessThan("3", { other: 5 })).toBe(true);
+    });
+
+    it("fails coercion when non-numeric string", () => {
+      expect(builtInValidationFunctions.lessThan("abc", { other: 5 })).toBe(
+        false,
+      );
+    });
+
+    it("passes for string comparison (ISO dates)", () => {
+      expect(
+        builtInValidationFunctions.lessThan("2026-01-01", {
+          other: "2026-06-15",
+        }),
+      ).toBe(true);
+    });
+
+    it("fails for equal strings", () => {
+      expect(
+        builtInValidationFunctions.lessThan("2026-01-01", {
+          other: "2026-01-01",
+        }),
+      ).toBe(false);
+    });
+
+    it("returns false when value is empty string", () => {
+      expect(builtInValidationFunctions.lessThan("", { other: 5 })).toBe(false);
+    });
+
+    it("returns false when other is empty string", () => {
+      expect(builtInValidationFunctions.lessThan(3, { other: "" })).toBe(false);
+    });
+
+    it("returns false when value is empty string vs non-empty string", () => {
+      expect(builtInValidationFunctions.lessThan("", { other: "abc" })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when other is empty string vs non-empty string", () => {
+      expect(builtInValidationFunctions.lessThan("abc", { other: "" })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when other is null", () => {
+      expect(builtInValidationFunctions.lessThan(3, { other: null })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when value is null", () => {
+      expect(builtInValidationFunctions.lessThan(null, { other: 5 })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when other is undefined", () => {
+      expect(builtInValidationFunctions.lessThan(3, { other: undefined })).toBe(
+        false,
+      );
+    });
+  });
+
+  describe("greaterThan", () => {
+    it("passes when value is greater than other", () => {
+      expect(builtInValidationFunctions.greaterThan(7, { other: 5 })).toBe(
+        true,
+      );
+    });
+
+    it("fails when value equals other", () => {
+      expect(builtInValidationFunctions.greaterThan(5, { other: 5 })).toBe(
+        false,
+      );
+    });
+
+    it("fails when value is less than other", () => {
+      expect(builtInValidationFunctions.greaterThan(3, { other: 5 })).toBe(
+        false,
+      );
+    });
+
+    it("coerces numeric string vs number", () => {
+      expect(builtInValidationFunctions.greaterThan("7", { other: 5 })).toBe(
+        true,
+      );
+    });
+
+    it("fails coercion when non-numeric string", () => {
+      expect(builtInValidationFunctions.greaterThan("abc", { other: 5 })).toBe(
+        false,
+      );
+    });
+
+    it("passes for string comparison (ISO dates)", () => {
+      expect(
+        builtInValidationFunctions.greaterThan("2026-06-15", {
+          other: "2026-01-01",
+        }),
+      ).toBe(true);
+    });
+
+    it("fails for lesser strings", () => {
+      expect(
+        builtInValidationFunctions.greaterThan("2026-01-01", {
+          other: "2026-06-15",
+        }),
+      ).toBe(false);
+    });
+
+    it("returns false when value is empty string", () => {
+      expect(builtInValidationFunctions.greaterThan("", { other: 5 })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when other is empty string", () => {
+      expect(builtInValidationFunctions.greaterThan(3, { other: "" })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when value is empty string vs non-empty string", () => {
+      expect(builtInValidationFunctions.greaterThan("", { other: "abc" })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when other is empty string vs non-empty string", () => {
+      expect(builtInValidationFunctions.greaterThan("abc", { other: "" })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when other is null", () => {
+      expect(builtInValidationFunctions.greaterThan(3, { other: null })).toBe(
+        false,
+      );
+    });
+
+    it("returns false when value is undefined", () => {
+      expect(
+        builtInValidationFunctions.greaterThan(undefined, { other: 5 }),
+      ).toBe(false);
+    });
+
+    it("returns false when value is null", () => {
+      expect(builtInValidationFunctions.greaterThan(null, { other: 5 })).toBe(
+        false,
+      );
+    });
+  });
+
+  describe("requiredIf", () => {
+    it("passes when condition is falsy (field not required)", () => {
+      expect(builtInValidationFunctions.requiredIf("", { field: false })).toBe(
+        true,
+      );
+      expect(builtInValidationFunctions.requiredIf("", { field: "" })).toBe(
+        true,
+      );
+      expect(builtInValidationFunctions.requiredIf("", { field: null })).toBe(
+        true,
+      );
+      expect(
+        builtInValidationFunctions.requiredIf("", { field: undefined }),
+      ).toBe(true);
+    });
+
+    it("fails when condition is truthy and value is empty", () => {
+      expect(builtInValidationFunctions.requiredIf("", { field: true })).toBe(
+        false,
+      );
+      expect(
+        builtInValidationFunctions.requiredIf(null, { field: "yes" }),
+      ).toBe(false);
+      expect(
+        builtInValidationFunctions.requiredIf(undefined, { field: 1 }),
+      ).toBe(false);
+    });
+
+    it("passes when condition is truthy and value is present", () => {
+      expect(
+        builtInValidationFunctions.requiredIf("hello", { field: true }),
+      ).toBe(true);
+      expect(builtInValidationFunctions.requiredIf(42, { field: true })).toBe(
+        true,
+      );
+    });
+  });
 });
 
 describe("runValidationCheck", () => {
@@ -391,6 +611,22 @@ describe("check helper", () => {
     });
   });
 
+  describe("numeric", () => {
+    it("creates numeric check with default message", () => {
+      const c = check.numeric();
+
+      expect(c.type).toBe("numeric");
+      expect(c.message).toBe("Must be a number");
+    });
+
+    it("creates numeric check with custom message", () => {
+      const c = check.numeric("Numbers only");
+
+      expect(c.type).toBe("numeric");
+      expect(c.message).toBe("Numbers only");
+    });
+  });
+
   describe("matches", () => {
     it("creates matches check with path reference", () => {
       const c = check.matches("/password", "Passwords must match");
@@ -400,4 +636,109 @@ describe("check helper", () => {
       expect(c.message).toBe("Passwords must match");
     });
   });
+
+  describe("equalTo", () => {
+    it("creates equalTo check with path reference", () => {
+      const c = check.equalTo("/email", "Emails must match");
+
+      expect(c.type).toBe("equalTo");
+      expect(c.args).toEqual({ other: { $state: "/email" } });
+      expect(c.message).toBe("Emails must match");
+    });
+  });
+
+  describe("lessThan", () => {
+    it("creates lessThan check with path reference", () => {
+      const c = check.lessThan("/maxValue", "Must be less");
+
+      expect(c.type).toBe("lessThan");
+      expect(c.args).toEqual({ other: { $state: "/maxValue" } });
+      expect(c.message).toBe("Must be less");
+    });
+  });
+
+  describe("greaterThan", () => {
+    it("creates greaterThan check with path reference", () => {
+      const c = check.greaterThan("/minValue");
+
+      expect(c.type).toBe("greaterThan");
+      expect(c.args).toEqual({ other: { $state: "/minValue" } });
+    });
+  });
+
+  describe("requiredIf", () => {
+    it("creates requiredIf check with path reference", () => {
+      const c = check.requiredIf("/toggle", "Required when toggle is on");
+
+      expect(c.type).toBe("requiredIf");
+      expect(c.args).toEqual({ field: { $state: "/toggle" } });
+      expect(c.message).toBe("Required when toggle is on");
+    });
+  });
+});
+
+// =============================================================================
+// Deep arg resolution in runValidationCheck
+// =============================================================================
+
+describe("deep arg resolution", () => {
+  it("resolves nested $state refs in validation args", () => {
+    const result = runValidationCheck(
+      {
+        type: "matches",
+        args: { other: { $state: "/form/password" } },
+        message: "Passwords must match",
+      },
+      {
+        value: "secret123",
+        stateModel: { form: { password: "secret123" } },
+      },
+    );
+    expect(result.valid).toBe(true);
+  });
+
+  it("resolves $state in cross-field lessThan check", () => {
+    const result = runValidationCheck(
+      {
+        type: "lessThan",
+        args: { other: { $state: "/form/maxPrice" } },
+        message: "Must be less than max price",
+      },
+      {
+        value: 50,
+        stateModel: { form: { maxPrice: 100 } },
+      },
+    );
+    expect(result.valid).toBe(true);
+  });
+
+  it("resolves $state in requiredIf check", () => {
+    const result = runValidationCheck(
+      {
+        type: "requiredIf",
+        args: { field: { $state: "/form/enableEmail" } },
+        message: "Email is required",
+      },
+      {
+        value: "",
+        stateModel: { form: { enableEmail: true } },
+      },
+    );
+    expect(result.valid).toBe(false);
+  });
+
+  it("passes requiredIf when condition is false", () => {
+    const result = runValidationCheck(
+      {
+        type: "requiredIf",
+        args: { field: { $state: "/form/enableEmail" } },
+        message: "Email is required",
+      },
+      {
+        value: "",
+        stateModel: { form: { enableEmail: false } },
+      },
+    );
+    expect(result.valid).toBe(true);
+  });
 });

packages/core/src/validation.ts

@@ -2,6 +2,7 @@ import { z } from "zod";
 import type { DynamicValue, StateModel, VisibilityCondition } from "./types";
 import { DynamicValueSchema, resolveDynamicValue } from "./types";
 import { VisibilityConditionSchema, evaluateVisibility } from "./visibility";
+import { resolvePropValue } from "./props";
 
 /**
  * Validation check definition
@@ -63,6 +64,14 @@ export interface ValidationFunctionDefinition {
   description?: string;
 }
 
+const matchesImpl: ValidationFunction = (
+  value: unknown,
+  args?: Record<string, unknown>,
+) => {
+  const other = args?.other;
+  return value === other;
+};
+
 /**
  * Built-in validation functions
  */
@@ -164,9 +173,64 @@ export const builtInValidationFunctions: Record<string, ValidationFunction> = {
   /**
    * Check if value matches another field
    */
-  matches: (value: unknown, args?: Record<string, unknown>) => {
+  matches: matchesImpl,
+
+  /**
+   * Alias for matches with a more descriptive name for cross-field equality
+   */
+  equalTo: matchesImpl,
+
+  /**
+   * Check if value is less than another field's value.
+   * Supports numbers, strings (useful for ISO date comparison), and
+   * cross-type numeric coercion (e.g. string "3" vs number 5).
+   */
+  lessThan: (value: unknown, args?: Record<string, unknown>) => {
     const other = args?.other;
-    return value === other;
+    if (value == null || other == null || value === "" || other === "")
+      return false;
+    if (typeof value === "number" && typeof other === "number")
+      return value < other;
+    if (typeof value === "string" && typeof other === "string")
+      return value < other;
+    const numVal = Number(value);
+    const numOther = Number(other);
+    if (!isNaN(numVal) && !isNaN(numOther)) return numVal < numOther;
+    return false;
+  },
+
+  /**
+   * Check if value is greater than another field's value.
+   * Supports numbers, strings (useful for ISO date comparison), and
+   * cross-type numeric coercion (e.g. string "7" vs number 5).
+   */
+  greaterThan: (value: unknown, args?: Record<string, unknown>) => {
+    const other = args?.other;
+    if (value == null || other == null || value === "" || other === "")
+      return false;
+    if (typeof value === "number" && typeof other === "number")
+      return value > other;
+    if (typeof value === "string" && typeof other === "string")
+      return value > other;
+    const numVal = Number(value);
+    const numOther = Number(other);
+    if (!isNaN(numVal) && !isNaN(numOther)) return numVal > numOther;
+    return false;
+  },
+
+  /**
+   * Required only when a condition is met.
+   * Uses JS truthiness: 0, false, "", null, and undefined are all
+   * treated as "condition not met" (field not required), matching
+   * the visibility system's bare-condition semantics.
+   */
+  requiredIf: (value: unknown, args?: Record<string, unknown>) => {
+    const condition = args?.field;
+    if (!condition) return true;
+    if (value === null || value === undefined) return false;
+    if (typeof value === "string") return value.trim().length > 0;
+    if (Array.isArray(value)) return value.length > 0;
+    return true;
   },
 };
 
@@ -209,11 +273,12 @@ export function runValidationCheck(
 ): ValidationCheckResult {
   const { value, stateModel, customFunctions } = ctx;
 
-  // Resolve args
+  // Resolve args using resolvePropValue so nested $state refs (and any other
+  // prop expressions) are handled consistently with the rest of the system.
   const resolvedArgs: Record<string, unknown> = {};
   if (check.args) {
     for (const [key, argValue] of Object.entries(check.args)) {
-      resolvedArgs[key] = resolveDynamicValue(argValue, stateModel);
+      resolvedArgs[key] = resolvePropValue(argValue, { stateModel });
     }
   }
 
@@ -326,6 +391,11 @@ export const check = {
     message,
   }),
 
+  numeric: (message = "Must be a number"): ValidationCheck => ({
+    type: "numeric",
+    message,
+  }),
+
   matches: (
     otherPath: string,
     message = "Fields must match",
@@ -334,4 +404,34 @@ export const check = {
     args: { other: { $state: otherPath } },
     message,
   }),
+
+  equalTo: (
+    otherPath: string,
+    message = "Fields must match",
+  ): ValidationCheck => ({
+    type: "equalTo",
+    args: { other: { $state: otherPath } },
+    message,
+  }),
+
+  lessThan: (otherPath: string, message?: string): ValidationCheck => ({
+    type: "lessThan",
+    args: { other: { $state: otherPath } },
+    message: message ?? "Must be less than the compared field",
+  }),
+
+  greaterThan: (otherPath: string, message?: string): ValidationCheck => ({
+    type: "greaterThan",
+    args: { other: { $state: otherPath } },
+    message: message ?? "Must be greater than the compared field",
+  }),
+
+  requiredIf: (
+    fieldPath: string,
+    message = "This field is required",
+  ): ValidationCheck => ({
+    type: "requiredIf",
+    args: { field: { $state: fieldPath } },
+    message,
+  }),
 };

packages/react/src/contexts/actions.tsx

@@ -17,6 +17,7 @@ import {
   type ResolvedAction,
 } from "@json-render/core";
 import { useStateStore } from "./state";
+import { useOptionalValidation } from "./validation";
 
 /**
  * Generate a unique ID for use with the "$id" token.
@@ -137,6 +138,7 @@ export function ActionProvider({
   children,
 }: ActionProviderProps) {
   const { get, set, getSnapshot } = useStateStore();
+  const validation = useOptionalValidation();
 
   const [handlers, setHandlers] =
     useState<Record<string, ActionHandler>>(initialHandlers);
@@ -227,13 +229,40 @@ export function ActionProvider({
           if (previousScreen) {
             set("/currentScreen", previousScreen);
           } else {
-            // Sentinel empty string = clear currentScreen (return to default)
             set("/currentScreen", undefined);
           }
         }
         return;
       }
 
+      // Built-in: validateForm triggers validateAll from the ValidationProvider
+      // and writes the result to a state path (default: /formValidation).
+      // IMPORTANT: validateAll() is synchronous — it runs all registered field
+      // validations and returns immediately. This guarantees that the next action
+      // in a sequential list (e.g. [validateForm, submitForm]) can read the
+      // validation result from state without awaiting an extra tick.
+      if (resolved.action === "validateForm") {
+        const validateAll = validation?.validateAll;
+        if (!validateAll) {
+          console.warn(
+            "validateForm action was dispatched but no ValidationProvider is connected. " +
+              "Ensure ValidationProvider is rendered inside the provider tree.",
+          );
+          return;
+        }
+        const valid = validateAll();
+        const errors: Record<string, string[]> = {};
+        for (const [path, fs] of Object.entries(validation.fieldStates)) {
+          if (fs.result && !fs.result.valid) {
+            errors[path] = fs.result.errors;
+          }
+        }
+        const statePath =
+          (resolved.params?.statePath as string) || "/formValidation";
+        set(statePath, { valid, errors });
+        return;
+      }
+
       const handler = handlers[resolved.action];
 
       if (!handler) {
@@ -300,7 +329,7 @@ export function ActionProvider({
         });
       }
     },
-    [handlers, get, set, getSnapshot, navigate],
+    [handlers, get, set, getSnapshot, navigate, validation],
   );
 
   const confirm = useCallback(() => {

packages/react/src/contexts/validation.tsx

@@ -3,10 +3,10 @@
 import React, {
   createContext,
   useContext,
+  useRef,
   useState,
   useCallback,
   useMemo,
-  useRef,
   type ReactNode,
 } from "react";
 import {
@@ -130,15 +130,14 @@ export function ValidationProvider({
   customFunctions = {},
   children,
 }: ValidationProviderProps) {
-  const { state } = useStateStore();
-  // Keep a ref to the latest state so `validate` doesn't change on every
-  // state update — preventing the entire validation context from churning.
-  const stateRef = useRef(state);
-  stateRef.current = state;
+  const { state, getSnapshot } = useStateStore();
 
   const [fieldStates, setFieldStates] = useState<
     Record<string, FieldValidationState>
   >({});
+  // Mutable mirror of fieldStates for synchronous reads (e.g. reading errors
+  // immediately after validateAll() before React flushes the batched setState).
+  const fieldStatesRef = useRef<Record<string, FieldValidationState>>({});
   const [fieldConfigs, setFieldConfigs] = useState<
     Record<string, ValidationConfig>
   >({});
@@ -160,8 +159,10 @@ export function ValidationProvider({
 
   const validate = useCallback(
     (path: string, config: ValidationConfig): ValidationResult => {
-      // Walk the nested state object using JSON Pointer segments
-      const currentState = stateRef.current;
+      // Read from the store directly so validation sees values written in the
+      // same synchronous handler (e.g. setValue then validate in onChange).
+      // Using React state would return the stale pre-render snapshot.
+      const currentState = getSnapshot();
       const segments = path.split("/").filter(Boolean);
       let value: unknown = currentState;
       for (const seg of segments) {
@@ -178,37 +179,39 @@ export function ValidationProvider({
         customFunctions,
       });
 
-      setFieldStates((prev) => ({
-        ...prev,
-        [path]: {
-          touched: prev[path]?.touched ?? true,
-          validated: true,
-          result,
-        },
-      }));
+      const newFieldState: FieldValidationState = {
+        touched: fieldStatesRef.current[path]?.touched ?? true,
+        validated: true,
+        result,
+      };
+      fieldStatesRef.current = {
+        ...fieldStatesRef.current,
+        [path]: newFieldState,
+      };
+      setFieldStates(fieldStatesRef.current);
 
       return result;
     },
-    [customFunctions],
+    [customFunctions, getSnapshot],
   );
 
   const touch = useCallback((path: string) => {
-    setFieldStates((prev) => ({
-      ...prev,
+    fieldStatesRef.current = {
+      ...fieldStatesRef.current,
       [path]: {
-        ...prev[path],
+        ...fieldStatesRef.current[path],
         touched: true,
-        validated: prev[path]?.validated ?? false,
-        result: prev[path]?.result ?? null,
+        validated: fieldStatesRef.current[path]?.validated ?? false,
+        result: fieldStatesRef.current[path]?.result ?? null,
       },
-    }));
+    };
+    setFieldStates(fieldStatesRef.current);
   }, []);
 
   const clear = useCallback((path: string) => {
-    setFieldStates((prev) => {
-      const { [path]: _, ...rest } = prev;
-      return rest;
-    });
+    const { [path]: _, ...rest } = fieldStatesRef.current;
+    fieldStatesRef.current = rest;
+    setFieldStates(rest);
   }, []);
 
   const validateAll = useCallback(() => {
@@ -227,7 +230,11 @@ export function ValidationProvider({
   const value = useMemo<ValidationContextValue>(
     () => ({
       customFunctions,
-      fieldStates,
+      // Getter returns the mutable ref so callers that read fieldStates
+      // synchronously after validateAll() see the latest values.
+      get fieldStates() {
+        return fieldStatesRef.current;
+      },
       validate,
       touch,
       clear,
@@ -236,6 +243,8 @@ export function ValidationProvider({
     }),
     [
       customFunctions,
+      // fieldStates (React state) stays in deps so the context value object
+      // is recreated on re-render, triggering downstream consumers.
       fieldStates,
       validate,
       touch,
@@ -263,6 +272,14 @@ export function useValidation(): ValidationContextValue {
   return ctx;
 }
 
+/**
+ * Non-throwing variant of useValidation.
+ * Returns null when no ValidationProvider is present.
+ */
+export function useOptionalValidation(): ValidationContextValue | null {
+  return useContext(ValidationContext);
+}
+
 /**
  * Hook to get validation state for a field
  */

packages/react/src/dynamic-forms.test.tsx

@@ -0,0 +1,773 @@
+import { describe, it, expect, vi } from "vitest";
+import React, { useState, useCallback, useMemo } from "react";
+import { render, act, fireEvent, screen } from "@testing-library/react";
+import type { Spec } from "@json-render/core";
+import {
+  JSONUIProvider,
+  Renderer,
+  type ComponentRenderProps,
+} from "./renderer";
+import { useStateStore } from "./contexts/state";
+import { useFieldValidation } from "./contexts/validation";
+import { useBoundProp } from "./hooks";
+
+// =============================================================================
+// Stub components
+// =============================================================================
+
+function Button({ element, emit }: ComponentRenderProps<{ label: string }>) {
+  return (
+    <button data-testid="btn" onClick={() => emit("press")}>
+      {element.props.label}
+    </button>
+  );
+}
+
+function Text({ element }: ComponentRenderProps<{ text: unknown }>) {
+  const value = element.props.text;
+  return (
+    <span data-testid="text">
+      {value == null
+        ? ""
+        : typeof value === "string"
+          ? value
+          : JSON.stringify(value)}
+    </span>
+  );
+}
+
+function InputField({
+  element,
+  bindings,
+}: ComponentRenderProps<{
+  label?: string;
+  value?: string;
+  checks?: Array<{
+    type: string;
+    message: string;
+    args?: Record<string, unknown>;
+  }>;
+}>) {
+  const props = element.props;
+  const [boundValue, setBoundValue] = useBoundProp<string>(
+    props.value as string | undefined,
+    bindings?.value,
+  );
+  const [localValue, setLocalValue] = useState("");
+  const isBound = !!bindings?.value;
+  const value = isBound ? (boundValue ?? "") : localValue;
+  const setValue = isBound ? setBoundValue : setLocalValue;
+
+  const hasValidation = !!(bindings?.value && props.checks?.length);
+  const config = useMemo(
+    () => (hasValidation ? { checks: props.checks ?? [] } : undefined),
+    [hasValidation, props.checks],
+  );
+  const { errors } = useFieldValidation(bindings?.value ?? "", config);
+
+  return (
+    <div>
+      {props.label && <label>{props.label}</label>}
+      <input
+        data-testid="input"
+        value={value}
+        onChange={(e) => setValue(e.target.value)}
+      />
+      {errors.length > 0 && <span data-testid="input-error">{errors[0]}</span>}
+    </div>
+  );
+}
+
+function SelectField({
+  element,
+  bindings,
+}: ComponentRenderProps<{ label?: string; value?: string }>) {
+  const props = element.props;
+  const [boundValue] = useBoundProp<string>(
+    props.value as string | undefined,
+    bindings?.value,
+  );
+  return <span data-testid="select-value">{boundValue ?? ""}</span>;
+}
+
+/**
+ * Select stub that mirrors the real shadcn Select validation behavior:
+ * calls setValue then validate() synchronously in onValueChange.
+ */
+function ValidatedSelect({
+  element,
+  bindings,
+  emit,
+}: ComponentRenderProps<{
+  label?: string;
+  name?: string;
+  options?: string[];
+  placeholder?: string;
+  value?: string;
+  checks?: Array<{
+    type: string;
+    message: string;
+    args?: Record<string, unknown>;
+  }>;
+  validateOn?: "change" | "blur" | "submit";
+}>) {
+  const props = element.props;
+  const [boundValue, setBoundValue] = useBoundProp<string>(
+    props.value as string | undefined,
+    bindings?.value,
+  );
+  const [localValue, setLocalValue] = useState("");
+  const isBound = !!bindings?.value;
+  const value = isBound ? (boundValue ?? "") : localValue;
+  const setValue = isBound ? setBoundValue : setLocalValue;
+  const validateOn = props.validateOn ?? "change";
+
+  const hasValidation = !!(bindings?.value && props.checks?.length);
+  const config = useMemo(
+    () =>
+      hasValidation ? { checks: props.checks ?? [], validateOn } : undefined,
+    [hasValidation, props.checks, validateOn],
+  );
+  const { errors, validate } = useFieldValidation(
+    bindings?.value ?? "",
+    config,
+  );
+
+  const options = props.options ?? [];
+
+  return (
+    <div>
+      {props.label && <label>{props.label}</label>}
+      <select
+        data-testid={`select-${props.name ?? "default"}`}
+        value={value}
+        onChange={(e) => {
+          setValue(e.target.value);
+          if (hasValidation && validateOn === "change") validate();
+          emit("change");
+        }}
+      >
+        <option value="">{props.placeholder ?? "Select..."}</option>
+        {options.map((opt) => (
+          <option key={opt} value={opt}>
+            {opt}
+          </option>
+        ))}
+      </select>
+      {errors.length > 0 && (
+        <span data-testid={`select-error-${props.name ?? "default"}`}>
+          {errors[0]}
+        </span>
+      )}
+    </div>
+  );
+}
+
+function StateProbe() {
+  const { state } = useStateStore();
+  return <pre data-testid="state-probe">{JSON.stringify(state)}</pre>;
+}
+
+const registry = { Button, Text, Input: InputField, Select: SelectField };
+
+function getState(): Record<string, unknown> {
+  return JSON.parse(screen.getByTestId("state-probe").textContent!);
+}
+
+// =============================================================================
+// $computed expressions in rendering
+// =============================================================================
+
+describe("$computed expressions in rendering", () => {
+  it("resolves a $computed prop using provided functions", async () => {
+    const spec: Spec = {
+      state: { first: "Jane", last: "Doe" },
+      root: "main",
+      elements: {
+        main: {
+          type: "Text",
+          props: {
+            text: {
+              $computed: "fullName",
+              args: {
+                first: { $state: "/first" },
+                last: { $state: "/last" },
+              },
+            },
+          },
+          children: [],
+        },
+      },
+    };
+
+    const functions = {
+      fullName: (args: Record<string, unknown>) => `${args.first} ${args.last}`,
+    };
+
+    render(
+      <JSONUIProvider
+        registry={registry}
+        initialState={spec.state}
+        functions={functions}
+      >
+        <Renderer spec={spec} registry={registry} />
+      </JSONUIProvider>,
+    );
+
+    expect(screen.getByTestId("text").textContent).toBe("Jane Doe");
+  });
+
+  it("renders gracefully when functions prop is omitted", async () => {
+    const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    const spec: Spec = {
+      state: {},
+      root: "main",
+      elements: {
+        main: {
+          type: "Text",
+          props: {
+            text: { $computed: "missing" },
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider registry={registry} initialState={spec.state}>
+        <Renderer spec={spec} registry={registry} />
+      </JSONUIProvider>,
+    );
+
+    expect(screen.getByTestId("text").textContent).toBe("");
+    warnSpy.mockRestore();
+  });
+});
+
+// =============================================================================
+// $template expressions in rendering
+// =============================================================================
+
+describe("$template expressions in rendering", () => {
+  it("interpolates state values into a template string", () => {
+    const spec: Spec = {
+      state: { user: { name: "Alice" }, count: 3 },
+      root: "main",
+      elements: {
+        main: {
+          type: "Text",
+          props: {
+            text: {
+              $template: "Hello, ${/user/name}! You have ${/count} messages.",
+            },
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider registry={registry} initialState={spec.state}>
+        <Renderer spec={spec} registry={registry} />
+      </JSONUIProvider>,
+    );
+
+    expect(screen.getByTestId("text").textContent).toBe(
+      "Hello, Alice! You have 3 messages.",
+    );
+  });
+
+  it("resolves missing paths to empty string", () => {
+    const spec: Spec = {
+      state: {},
+      root: "main",
+      elements: {
+        main: {
+          type: "Text",
+          props: {
+            text: { $template: "Hi ${/name}!" },
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider registry={registry} initialState={spec.state}>
+        <Renderer spec={spec} registry={registry} />
+      </JSONUIProvider>,
+    );
+
+    expect(screen.getByTestId("text").textContent).toBe("Hi !");
+  });
+});
+
+// =============================================================================
+// Watchers
+// =============================================================================
+
+describe("watchers (watch field)", () => {
+  it("does not fire on initial render, fires when watched state changes", async () => {
+    const loadCities = vi.fn(async (params: Record<string, unknown>) => {
+      // no-op, just tracking the call
+    });
+
+    const spec: Spec = {
+      state: { form: { country: "" }, citiesLoaded: false },
+      root: "main",
+      elements: {
+        main: {
+          type: "Button",
+          props: { label: "Set Country" },
+          on: {
+            press: [
+              {
+                action: "setState",
+                params: { statePath: "/form/country", value: "US" },
+              },
+            ],
+          },
+          children: [],
+        },
+        watcher: {
+          type: "Select",
+          props: { value: { $state: "/form/country" } },
+          watch: {
+            "/form/country": {
+              action: "loadCities",
+              params: { country: { $state: "/form/country" } },
+            },
+          },
+          children: [],
+        },
+      },
+    };
+
+    // Add watcher as a child of a wrapper so both render
+    const wrapperSpec: Spec = {
+      ...spec,
+      root: "wrapper",
+      elements: {
+        ...spec.elements,
+        wrapper: {
+          type: "Button",
+          props: { label: "wrapper" },
+          children: ["main", "watcher"],
+        },
+      },
+    };
+
+    // Use a Stack-like wrapper -- but since we only have Button/Text/Select
+    // stubs, we need a container. Let's add a simple Stack stub.
+    const Stack = ({
+      children,
+    }: ComponentRenderProps<Record<string, unknown>>) => {
+      return <div data-testid="stack">{children}</div>;
+    };
+    const reg = { ...registry, Stack };
+
+    const stackSpec: Spec = {
+      state: { form: { country: "" }, citiesLoaded: false },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["btn", "watcher"],
+        },
+        btn: {
+          type: "Button",
+          props: { label: "Set Country" },
+          on: {
+            press: [
+              {
+                action: "setState",
+                params: { statePath: "/form/country", value: "US" },
+              },
+            ],
+          },
+          children: [],
+        },
+        watcher: {
+          type: "Select",
+          props: { value: { $state: "/form/country" } },
+          watch: {
+            "/form/country": {
+              action: "loadCities",
+              params: { country: { $state: "/form/country" } },
+            },
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider
+        registry={reg}
+        initialState={stackSpec.state}
+        handlers={{ loadCities }}
+      >
+        <Renderer spec={stackSpec} registry={reg} />
+        <StateProbe />
+      </JSONUIProvider>,
+    );
+
+    // Not called on initial render
+    expect(loadCities).not.toHaveBeenCalled();
+
+    // Change the watched state path
+    await act(async () => {
+      fireEvent.click(screen.getByTestId("btn"));
+    });
+
+    expect(loadCities).toHaveBeenCalledTimes(1);
+    expect(loadCities).toHaveBeenCalledWith(
+      expect.objectContaining({ country: "US" }),
+    );
+  });
+
+  it("fires multiple action bindings on the same watch path", async () => {
+    const action1 = vi.fn();
+    const action2 = vi.fn();
+
+    const Stack = ({
+      children,
+    }: ComponentRenderProps<Record<string, unknown>>) => <div>{children}</div>;
+    const reg = { ...registry, Stack };
+
+    const spec: Spec = {
+      state: { value: "a" },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["btn", "watcher"],
+        },
+        btn: {
+          type: "Button",
+          props: { label: "Change" },
+          on: {
+            press: [
+              {
+                action: "setState",
+                params: { statePath: "/value", value: "b" },
+              },
+            ],
+          },
+          children: [],
+        },
+        watcher: {
+          type: "Text",
+          props: { text: { $state: "/value" } },
+          watch: {
+            "/value": [{ action: "action1" }, { action: "action2" }],
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider
+        registry={reg}
+        initialState={spec.state}
+        handlers={{ action1, action2 }}
+      >
+        <Renderer spec={spec} registry={reg} />
+      </JSONUIProvider>,
+    );
+
+    await act(async () => {
+      fireEvent.click(screen.getByTestId("btn"));
+    });
+
+    expect(action1).toHaveBeenCalledTimes(1);
+    expect(action2).toHaveBeenCalledTimes(1);
+  });
+});
+
+// =============================================================================
+// validateForm action
+// =============================================================================
+
+describe("validateForm action", () => {
+  it("writes { valid: false } when a required field is empty", async () => {
+    const Stack = ({
+      children,
+    }: ComponentRenderProps<Record<string, unknown>>) => <div>{children}</div>;
+    const reg = { ...registry, Stack };
+
+    const spec: Spec = {
+      state: { form: { email: "" }, result: null },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["emailInput", "submitBtn"],
+        },
+        emailInput: {
+          type: "Input",
+          props: {
+            label: "Email",
+            value: { $bindState: "/form/email" },
+            checks: [{ type: "required", message: "Email is required" }],
+          },
+          children: [],
+        },
+        submitBtn: {
+          type: "Button",
+          props: { label: "Submit" },
+          on: {
+            press: [
+              {
+                action: "validateForm",
+                params: { statePath: "/result" },
+              },
+            ],
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider registry={reg} initialState={spec.state}>
+        <Renderer spec={spec} registry={reg} />
+        <StateProbe />
+      </JSONUIProvider>,
+    );
+
+    // Click submit with empty email
+    await act(async () => {
+      fireEvent.click(screen.getByTestId("btn"));
+    });
+
+    const state = getState();
+    expect(state.result).toEqual({
+      valid: false,
+      errors: { "/form/email": ["Email is required"] },
+    });
+  });
+
+  it("writes { valid: true } when all fields pass validation", async () => {
+    const Stack = ({
+      children,
+    }: ComponentRenderProps<Record<string, unknown>>) => <div>{children}</div>;
+    const reg = { ...registry, Stack };
+
+    const spec: Spec = {
+      state: { form: { email: "test@example.com" }, result: null },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["emailInput", "submitBtn"],
+        },
+        emailInput: {
+          type: "Input",
+          props: {
+            label: "Email",
+            value: { $bindState: "/form/email" },
+            checks: [{ type: "required", message: "Email is required" }],
+          },
+          children: [],
+        },
+        submitBtn: {
+          type: "Button",
+          props: { label: "Submit" },
+          on: {
+            press: [
+              {
+                action: "validateForm",
+                params: { statePath: "/result" },
+              },
+            ],
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider registry={reg} initialState={spec.state}>
+        <Renderer spec={spec} registry={reg} />
+        <StateProbe />
+      </JSONUIProvider>,
+    );
+
+    await act(async () => {
+      fireEvent.click(screen.getByTestId("btn"));
+    });
+
+    const state = getState();
+    expect(state.result).toEqual({ valid: true, errors: {} });
+  });
+
+  it("defaults to /formValidation when no statePath is provided", async () => {
+    const Stack = ({
+      children,
+    }: ComponentRenderProps<Record<string, unknown>>) => <div>{children}</div>;
+    const reg = { ...registry, Stack };
+
+    const spec: Spec = {
+      state: { form: { name: "filled" } },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["nameInput", "submitBtn"],
+        },
+        nameInput: {
+          type: "Input",
+          props: {
+            label: "Name",
+            value: { $bindState: "/form/name" },
+            checks: [{ type: "required", message: "Required" }],
+          },
+          children: [],
+        },
+        submitBtn: {
+          type: "Button",
+          props: { label: "Submit" },
+          on: {
+            press: [{ action: "validateForm" }],
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider registry={reg} initialState={spec.state}>
+        <Renderer spec={spec} registry={reg} />
+        <StateProbe />
+      </JSONUIProvider>,
+    );
+
+    await act(async () => {
+      fireEvent.click(screen.getByTestId("btn"));
+    });
+
+    const state = getState();
+    expect(state.formValidation).toEqual({ valid: true, errors: {} });
+  });
+});
+
+// =============================================================================
+// Select validate-on-change timing (#151)
+// =============================================================================
+
+describe("Select validate-on-change sees the new value, not the stale value", () => {
+  const Stack = ({
+    children,
+  }: ComponentRenderProps<Record<string, unknown>>) => <div>{children}</div>;
+
+  const regWithSelect = {
+    ...registry,
+    Stack,
+    Select: ValidatedSelect,
+  };
+
+  it("does not show 'required' error when selecting the first value", async () => {
+    const spec: Spec = {
+      state: { form: { country: "" } },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["countrySelect"],
+        },
+        countrySelect: {
+          type: "Select",
+          props: {
+            label: "Country",
+            name: "country",
+            options: ["US", "Canada", "UK"],
+            placeholder: "Choose a country",
+            value: { $bindState: "/form/country" },
+            checks: [{ type: "required", message: "Country is required" }],
+            validateOn: "change",
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider registry={regWithSelect} initialState={spec.state}>
+        <Renderer spec={spec} registry={regWithSelect} />
+        <StateProbe />
+      </JSONUIProvider>,
+    );
+
+    // Select "US" for the first time (from empty)
+    await act(async () => {
+      fireEvent.change(screen.getByTestId("select-country"), {
+        target: { value: "US" },
+      });
+    });
+
+    // The value should be set in state
+    const state = getState();
+    expect((state.form as Record<string, unknown>).country).toBe("US");
+
+    // No validation error should appear -- "US" is non-empty
+    expect(screen.queryByTestId("select-error-country")).toBeNull();
+  });
+
+  it("does not show 'required' error when selecting the first city after country change resets it", async () => {
+    const spec: Spec = {
+      state: {
+        form: { country: "US", city: "" },
+        availableCities: ["New York", "Chicago"],
+      },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["citySelect"],
+        },
+        citySelect: {
+          type: "Select",
+          props: {
+            label: "City",
+            name: "city",
+            options: ["New York", "Chicago"],
+            placeholder: "Select a city",
+            value: { $bindState: "/form/city" },
+            checks: [{ type: "required", message: "City is required" }],
+            validateOn: "change",
+          },
+          children: [],
+        },
+      },
+    };
+
+    render(
+      <JSONUIProvider registry={regWithSelect} initialState={spec.state}>
+        <Renderer spec={spec} registry={regWithSelect} />
+        <StateProbe />
+      </JSONUIProvider>,
+    );
+
+    // Select "New York" for the first time (from empty)
+    await act(async () => {
+      fireEvent.change(screen.getByTestId("select-city"), {
+        target: { value: "New York" },
+      });
+    });
+
+    const state = getState();
+    expect((state.form as Record<string, unknown>).city).toBe("New York");
+
+    // No validation error should appear
+    expect(screen.queryByTestId("select-error-city")).toBeNull();
+  });
+});

packages/react/src/index.ts

@@ -30,6 +30,7 @@ export {
 export {
   ValidationProvider,
   useValidation,
+  useOptionalValidation,
   useFieldValidation,
   type ValidationContextValue,
   type ValidationProviderProps,

packages/react/src/renderer.tsx

@@ -5,7 +5,9 @@ import React, {
   type ErrorInfo,
   type ReactNode,
   useCallback,
+  useEffect,
   useMemo,
+  useRef,
 } from "react";
 import type {
   UIElement,
@@ -14,6 +16,7 @@ import type {
   Catalog,
   SchemaDefinition,
   StateStore,
+  ComputedFunction,
 } from "@json-render/core";
 import {
   resolveElementProps,
@@ -136,6 +139,19 @@ class ElementErrorBoundary extends React.Component<
   }
 }
 
+// ---------------------------------------------------------------------------
+// FunctionsContext – provides $computed functions to the element tree
+// ---------------------------------------------------------------------------
+
+const EMPTY_FUNCTIONS: Record<string, ComputedFunction> = {};
+
+const FunctionsContext =
+  React.createContext<Record<string, ComputedFunction>>(EMPTY_FUNCTIONS);
+
+function useFunctions(): Record<string, ComputedFunction> {
+  return React.useContext(FunctionsContext);
+}
+
 interface ElementRendererProps {
   element: UIElement;
   spec: Spec;
@@ -158,21 +174,22 @@ const ElementRenderer = React.memo(function ElementRenderer({
   const repeatScope = useRepeatScope();
   const { ctx } = useVisibility();
   const { execute } = useActions();
-  const { getSnapshot } = useStateStore();
+  const { getSnapshot, state: watchState } = useStateStore();
+  const functions = useFunctions();
 
-  // Build context with repeat scope (used for both visibility and props)
-  const fullCtx: PropResolutionContext = useMemo(
-    () =>
-      repeatScope
-        ? {
-            ...ctx,
-            repeatItem: repeatScope.item,
-            repeatIndex: repeatScope.index,
-            repeatBasePath: repeatScope.basePath,
-          }
-        : ctx,
-    [ctx, repeatScope],
-  );
+  // Build context with repeat scope and $computed functions
+  const fullCtx: PropResolutionContext = useMemo(() => {
+    const base: PropResolutionContext = repeatScope
+      ? {
+          ...ctx,
+          repeatItem: repeatScope.item,
+          repeatIndex: repeatScope.index,
+          repeatBasePath: repeatScope.basePath,
+        }
+      : { ...ctx };
+    base.functions = functions;
+    return base;
+  }, [ctx, repeatScope, functions]);
 
   // Evaluate visibility (now supports $item/$index inside repeat scopes)
   const isVisible =
@@ -227,6 +244,85 @@ const ElementRenderer = React.memo(function ElementRenderer({
     [onBindings, emit],
   );
 
+  // Watch effect: fire actions when watched state paths change.
+  // Must be called before any early return to satisfy Rules of Hooks.
+  //
+  // Two refs serve distinct roles:
+  // - `stableWatchRef` (useMemo): holds the last emitted values object so we
+  //   can return the same reference when watched values haven't changed,
+  //   preventing the downstream useEffect from firing on unrelated state updates.
+  // - `prevWatchValues` (useEffect): tracks the previous watched-values snapshot
+  //   for change detection. Starts as `null` to skip the initial mount.
+  const watchConfig = element.watch;
+  const prevWatchValues = useRef<Record<string, unknown> | null>(null);
+  const stableWatchRef = useRef<Record<string, unknown> | undefined>(undefined);
+
+  const watchedValues = useMemo(() => {
+    if (!watchConfig) return undefined;
+    const values: Record<string, unknown> = {};
+    for (const path of Object.keys(watchConfig)) {
+      values[path] = getByPath(watchState, path);
+    }
+    const prev = stableWatchRef.current;
+    if (prev) {
+      const keys = Object.keys(values);
+      if (
+        keys.length === Object.keys(prev).length &&
+        keys.every((k) => values[k] === prev[k])
+      ) {
+        return prev;
+      }
+    }
+    stableWatchRef.current = values;
+    return values;
+  }, [watchConfig, watchState]);
+
+  useEffect(() => {
+    if (!watchConfig || !watchedValues) return;
+    const paths = Object.keys(watchConfig);
+    if (paths.length === 0) return;
+
+    const prev = prevWatchValues.current;
+    prevWatchValues.current = watchedValues;
+
+    // Skip the initial mount — only fire on changes
+    if (prev === null) return;
+
+    let cancelled = false;
+    void (async () => {
+      for (const path of paths) {
+        if (cancelled) break;
+        if (watchedValues[path] !== prev[path]) {
+          const binding = watchConfig[path];
+          if (!binding) continue;
+          const bindings = Array.isArray(binding) ? binding : [binding];
+          for (const b of bindings) {
+            if (cancelled) break;
+            if (!b.params) {
+              await execute(b);
+              if (cancelled) break;
+              continue;
+            }
+            const liveCtx: PropResolutionContext = {
+              ...fullCtx,
+              stateModel: getSnapshot(),
+            };
+            const resolved: Record<string, unknown> = {};
+            for (const [key, val] of Object.entries(b.params)) {
+              resolved[key] = resolveActionParam(val, liveCtx);
+            }
+            await execute({ ...b, params: resolved });
+            if (cancelled) break;
+          }
+        }
+      }
+    })().catch(console.error);
+
+    return () => {
+      cancelled = true;
+    };
+  }, [watchConfig, watchedValues, execute, fullCtx, getSnapshot]);
+
   // Don't render if not visible
   if (!isVisible) {
     return null;
@@ -419,6 +515,8 @@ export interface JSONUIProviderProps {
     string,
     (value: unknown, args?: Record<string, unknown>) => boolean
   >;
+  /** Named functions for `$computed` expressions in props */
+  functions?: Record<string, ComputedFunction>;
   /** Callback when state changes (uncontrolled mode) */
   onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
   children: ReactNode;
@@ -434,6 +532,7 @@ export function JSONUIProvider({
   handlers,
   navigate,
   validationFunctions,
+  functions,
   onStateChange,
   children,
 }: JSONUIProviderProps) {
@@ -444,12 +543,14 @@ export function JSONUIProvider({
       onStateChange={onStateChange}
     >
       <VisibilityProvider>
-        <ActionProvider handlers={handlers} navigate={navigate}>
-          <ValidationProvider customFunctions={validationFunctions}>
-            {children}
-            <ConfirmationDialogManager />
-          </ValidationProvider>
-        </ActionProvider>
+        <ValidationProvider customFunctions={validationFunctions}>
+          <ActionProvider handlers={handlers} navigate={navigate}>
+            <FunctionsContext.Provider value={functions ?? EMPTY_FUNCTIONS}>
+              {children}
+              <ConfirmationDialogManager />
+            </FunctionsContext.Provider>
+          </ActionProvider>
+        </ValidationProvider>
       </VisibilityProvider>
     </StateProvider>
   );
@@ -650,6 +751,8 @@ export interface CreateRendererProps {
   onAction?: (actionName: string, params?: Record<string, unknown>) => void;
   /** Callback when state changes (uncontrolled mode) */
   onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
+  /** Named functions for `$computed` expressions in props */
+  functions?: Record<string, ComputedFunction>;
   /** Whether the spec is currently loading/streaming */
   loading?: boolean;
   /** Fallback component for unknown types */
@@ -703,6 +806,7 @@ export function createRenderer<
     state,
     onAction,
     onStateChange,
+    functions,
     loading,
     fallback,
   }: CreateRendererProps) {
@@ -730,17 +834,19 @@ export function createRenderer<
         onStateChange={onStateChange}
       >
         <VisibilityProvider>
-          <ActionProvider handlers={actionHandlers}>
-            <ValidationProvider>
-              <Renderer
-                spec={spec}
-                registry={registry}
-                loading={loading}
-                fallback={fallback}
-              />
-              <ConfirmationDialogManager />
-            </ValidationProvider>
-          </ActionProvider>
+          <ValidationProvider>
+            <ActionProvider handlers={actionHandlers}>
+              <FunctionsContext.Provider value={functions ?? EMPTY_FUNCTIONS}>
+                <Renderer
+                  spec={spec}
+                  registry={registry}
+                  loading={loading}
+                  fallback={fallback}
+                />
+                <ConfirmationDialogManager />
+              </FunctionsContext.Provider>
+            </ActionProvider>
+          </ValidationProvider>
         </VisibilityProvider>
       </StateProvider>
     );

packages/react/src/schema.ts

@@ -67,6 +67,11 @@ export const schema = defineSchema(
         description:
           "Remove an item from an array in state by index. Params: { statePath: string, index: number }",
       },
+      {
+        name: "validateForm",
+        description:
+          "Validate all registered form fields and write the result to state. Params: { statePath?: string }. Defaults to /formValidation. Result: { valid: boolean, errors: Record<string, string[]> }.",
+      },
     ],
     defaultRules: [
       // Element integrity

packages/shadcn/src/catalog.ts

@@ -1,5 +1,21 @@
 import { z } from "zod";
 
+// =============================================================================
+// Shared validation schemas used across form components
+// =============================================================================
+
+const validationCheckSchema = z
+  .array(
+    z.object({
+      type: z.string(),
+      message: z.string(),
+      args: z.record(z.string(), z.unknown()).optional(),
+    }),
+  )
+  .nullable();
+
+const validateOnSchema = z.enum(["change", "blur", "submit"]).nullable();
+
 // =============================================================================
 // shadcn/ui Component Definitions
 // =============================================================================
@@ -272,19 +288,12 @@ export const shadcnComponentDefinitions = {
       type: z.enum(["text", "email", "password", "number"]).nullable(),
       placeholder: z.string().nullable(),
       value: z.string().nullable(),
-      checks: z
-        .array(
-          z.object({
-            type: z.string(),
-            message: z.string(),
-            args: z.record(z.string(), z.unknown()).optional(),
-          }),
-        )
-        .nullable(),
+      checks: validationCheckSchema,
+      validateOn: validateOnSchema,
     }),
     events: ["submit", "focus", "blur"],
     description:
-      "Text input field. Use { $bindState } on value for two-way binding. Use checks for validation (e.g. required, email, minLength).",
+      "Text input field. Use { $bindState } on value for two-way binding. Use checks for validation (e.g. required, email, minLength). validateOn controls timing (default: blur).",
     example: {
       label: "Email",
       name: "email",
@@ -300,18 +309,11 @@ export const shadcnComponentDefinitions = {
       placeholder: z.string().nullable(),
       rows: z.number().nullable(),
       value: z.string().nullable(),
-      checks: z
-        .array(
-          z.object({
-            type: z.string(),
-            message: z.string(),
-            args: z.record(z.string(), z.unknown()).optional(),
-          }),
-        )
-        .nullable(),
+      checks: validationCheckSchema,
+      validateOn: validateOnSchema,
     }),
     description:
-      "Multi-line text input. Use { $bindState } on value for binding. Use checks for validation.",
+      "Multi-line text input. Use { $bindState } on value for binding. Use checks for validation. validateOn controls timing (default: blur).",
   },
 
   Select: {
@@ -321,19 +323,12 @@ export const shadcnComponentDefinitions = {
       options: z.array(z.string()),
       placeholder: z.string().nullable(),
       value: z.string().nullable(),
-      checks: z
-        .array(
-          z.object({
-            type: z.string(),
-            message: z.string(),
-            args: z.record(z.string(), z.unknown()).optional(),
-          }),
-        )
-        .nullable(),
+      checks: validationCheckSchema,
+      validateOn: validateOnSchema,
     }),
     events: ["change"],
     description:
-      "Dropdown select input. Use { $bindState } on value for binding. Use checks for validation.",
+      "Dropdown select input. Use { $bindState } on value for binding. Use checks for validation. validateOn controls timing (default: change).",
   },
 
   Checkbox: {
@@ -341,9 +336,12 @@ export const shadcnComponentDefinitions = {
       label: z.string(),
       name: z.string(),
       checked: z.boolean().nullable(),
+      checks: validationCheckSchema,
+      validateOn: validateOnSchema,
     }),
     events: ["change"],
-    description: "Checkbox input. Use { $bindState } on checked for binding.",
+    description:
+      "Checkbox input. Use { $bindState } on checked for binding. Use checks for validation. validateOn controls timing (default: change).",
   },
 
   Radio: {
@@ -352,9 +350,12 @@ export const shadcnComponentDefinitions = {
       name: z.string(),
       options: z.array(z.string()),
       value: z.string().nullable(),
+      checks: validationCheckSchema,
+      validateOn: validateOnSchema,
     }),
     events: ["change"],
-    description: "Radio button group. Use { $bindState } on value for binding.",
+    description:
+      "Radio button group. Use { $bindState } on value for binding. Use checks for validation. validateOn controls timing (default: change).",
   },
 
   Switch: {
@@ -362,9 +363,12 @@ export const shadcnComponentDefinitions = {
       label: z.string(),
       name: z.string(),
       checked: z.boolean().nullable(),
+      checks: validationCheckSchema,
+      validateOn: validateOnSchema,
     }),
     events: ["change"],
-    description: "Toggle switch. Use { $bindState } on checked for binding.",
+    description:
+      "Toggle switch. Use { $bindState } on checked for binding. Use checks for validation. validateOn controls timing (default: change).",
   },
 
   Slider: {

packages/shadcn/src/components.tsx

@@ -664,11 +664,12 @@ export const shadcnComponents = {
     const isBound = !!bindings?.value;
     const value = isBound ? (boundValue ?? "") : localValue;
     const setValue = isBound ? setBoundValue : setLocalValue;
+    const validateOn = props.validateOn ?? "blur";
 
     const hasValidation = !!(bindings?.value && props.checks?.length);
     const { errors, validate } = useFieldValidation(
       bindings?.value ?? "",
-      hasValidation ? { checks: props.checks ?? [] } : undefined,
+      hasValidation ? { checks: props.checks ?? [], validateOn } : undefined,
     );
 
     return (
@@ -682,13 +683,16 @@ export const shadcnComponents = {
           type={props.type ?? "text"}
           placeholder={props.placeholder ?? ""}
           value={value}
-          onChange={(e) => setValue(e.target.value)}
+          onChange={(e) => {
+            setValue(e.target.value);
+            if (hasValidation && validateOn === "change") validate();
+          }}
           onKeyDown={(e) => {
             if (e.key === "Enter") emit("submit");
           }}
           onFocus={() => emit("focus")}
           onBlur={() => {
-            if (hasValidation) validate();
+            if (hasValidation && validateOn === "blur") validate();
             emit("blur");
           }}
         />
@@ -711,11 +715,12 @@ export const shadcnComponents = {
     const isBound = !!bindings?.value;
     const value = isBound ? (boundValue ?? "") : localValue;
     const setValue = isBound ? setBoundValue : setLocalValue;
+    const validateOn = props.validateOn ?? "blur";
 
     const hasValidation = !!(bindings?.value && props.checks?.length);
     const { errors, validate } = useFieldValidation(
       bindings?.value ?? "",
-      hasValidation ? { checks: props.checks ?? [] } : undefined,
+      hasValidation ? { checks: props.checks ?? [], validateOn } : undefined,
     );
 
     return (
@@ -729,9 +734,12 @@ export const shadcnComponents = {
           placeholder={props.placeholder ?? ""}
           rows={props.rows ?? 3}
           value={value}
-          onChange={(e) => setValue(e.target.value)}
+          onChange={(e) => {
+            setValue(e.target.value);
+            if (hasValidation && validateOn === "change") validate();
+          }}
           onBlur={() => {
-            if (hasValidation) validate();
+            if (hasValidation && validateOn === "blur") validate();
           }}
         />
         {errors.length > 0 && (
@@ -758,11 +766,12 @@ export const shadcnComponents = {
     const options = rawOptions.map((opt) =>
       typeof opt === "string" ? opt : String(opt ?? ""),
     );
+    const validateOn = props.validateOn ?? "change";
 
     const hasValidation = !!(bindings?.value && props.checks?.length);
     const { errors, validate } = useFieldValidation(
       bindings?.value ?? "",
-      hasValidation ? { checks: props.checks ?? [] } : undefined,
+      hasValidation ? { checks: props.checks ?? [], validateOn } : undefined,
     );
 
     return (
@@ -772,7 +781,8 @@ export const shadcnComponents = {
           value={value}
           onValueChange={(v) => {
             setValue(v);
-            if (hasValidation) validate();
+            // Select has no native blur event, so only validate on "change"
+            if (hasValidation && validateOn === "change") validate();
             emit("change");
           }}
         >
@@ -808,19 +818,32 @@ export const shadcnComponents = {
     const checked = isBound ? (boundChecked ?? false) : localChecked;
     const setChecked = isBound ? setBoundChecked : setLocalChecked;
 
+    const validateOn = props.validateOn ?? "change";
+    const hasValidation = !!(bindings?.checked && props.checks?.length);
+    const { errors, validate } = useFieldValidation(
+      bindings?.checked ?? "",
+      hasValidation ? { checks: props.checks ?? [], validateOn } : undefined,
+    );
+
     return (
-      <div className="flex items-center space-x-2">
-        <Checkbox
-          id={props.name ?? undefined}
-          checked={checked}
-          onCheckedChange={(c) => {
-            setChecked(c === true);
-            emit("change");
-          }}
-        />
-        <Label htmlFor={props.name ?? undefined} className="cursor-pointer">
-          {props.label}
-        </Label>
+      <div className="space-y-1">
+        <div className="flex items-center space-x-2">
+          <Checkbox
+            id={props.name ?? undefined}
+            checked={checked}
+            onCheckedChange={(c) => {
+              setChecked(c === true);
+              if (hasValidation && validateOn === "change") validate();
+              emit("change");
+            }}
+          />
+          <Label htmlFor={props.name ?? undefined} className="cursor-pointer">
+            {props.label}
+          </Label>
+        </div>
+        {errors.length > 0 && (
+          <p className="text-sm text-destructive">{errors[0]}</p>
+        )}
       </div>
     );
   },
@@ -843,6 +866,13 @@ export const shadcnComponents = {
     const value = isBound ? (boundValue ?? "") : localValue;
     const setValue = isBound ? setBoundValue : setLocalValue;
 
+    const validateOn = props.validateOn ?? "change";
+    const hasValidation = !!(bindings?.value && props.checks?.length);
+    const { errors, validate } = useFieldValidation(
+      bindings?.value ?? "",
+      hasValidation ? { checks: props.checks ?? [], validateOn } : undefined,
+    );
+
     return (
       <div className="space-y-2">
         {props.label && <Label>{props.label}</Label>}
@@ -850,6 +880,7 @@ export const shadcnComponents = {
           value={value}
           onValueChange={(v) => {
             setValue(v);
+            if (hasValidation && validateOn === "change") validate();
             emit("change");
           }}
         >
@@ -868,6 +899,9 @@ export const shadcnComponents = {
             </div>
           ))}
         </RadioGroup>
+        {errors.length > 0 && (
+          <p className="text-sm text-destructive">{errors[0]}</p>
+        )}
       </div>
     );
   },
@@ -886,19 +920,32 @@ export const shadcnComponents = {
     const checked = isBound ? (boundChecked ?? false) : localChecked;
     const setChecked = isBound ? setBoundChecked : setLocalChecked;
 
+    const validateOn = props.validateOn ?? "change";
+    const hasValidation = !!(bindings?.checked && props.checks?.length);
+    const { errors, validate } = useFieldValidation(
+      bindings?.checked ?? "",
+      hasValidation ? { checks: props.checks ?? [], validateOn } : undefined,
+    );
+
     return (
-      <div className="flex items-center justify-between space-x-2">
-        <Label htmlFor={props.name ?? undefined} className="cursor-pointer">
-          {props.label}
-        </Label>
-        <Switch
-          id={props.name ?? undefined}
-          checked={checked}
-          onCheckedChange={(c) => {
-            setChecked(c);
-            emit("change");
-          }}
-        />
+      <div className="space-y-1">
+        <div className="flex items-center justify-between space-x-2">
+          <Label htmlFor={props.name ?? undefined} className="cursor-pointer">
+            {props.label}
+          </Label>
+          <Switch
+            id={props.name ?? undefined}
+            checked={checked}
+            onCheckedChange={(c) => {
+              setChecked(c);
+              if (hasValidation && validateOn === "change") validate();
+              emit("change");
+            }}
+          />
+        </div>
+        {errors.length > 0 && (
+          <p className="text-sm text-destructive">{errors[0]}</p>
+        )}
       </div>
     );
   },

packages/vue/README.md

@@ -0,0 +1,496 @@
+# @json-render/vue
+
+Vue 3 renderer for json-render. Turn JSON specs into Vue components with data binding, visibility, and actions.
+
+## Installation
+
+```bash
+npm install @json-render/vue @json-render/core zod
+```
+
+Peer dependencies: `vue ^3.5.0` and `zod ^4.0.0`.
+
+## Quick Start
+
+### 1. Create a Catalog
+
+```typescript
+import { defineCatalog } from "@json-render/core";
+import { schema } from "@json-render/vue/schema";
+import { z } from "zod";
+
+export const catalog = defineCatalog(schema, {
+  components: {
+    Card: {
+      props: z.object({
+        title: z.string(),
+        description: z.string().nullable(),
+      }),
+      description: "A card container",
+    },
+    Button: {
+      props: z.object({
+        label: z.string(),
+        action: z.string(),
+      }),
+      description: "A clickable button",
+    },
+    Input: {
+      props: z.object({
+        value: z.union([z.string(), z.record(z.unknown())]).nullable(),
+        label: z.string(),
+        placeholder: z.string().nullable(),
+      }),
+      description: "Text input field with optional value binding",
+    },
+  },
+  actions: {
+    submit: { description: "Submit the form" },
+    cancel: { description: "Cancel and close" },
+  },
+});
+```
+
+### 2. Define Component Implementations
+
+Components are written using Vue's `h()` render function. `children` is a `VNode | VNode[]` — pass it directly to your container element.
+
+`defineRegistry` conditionally requires the `actions` field only when the catalog declares actions. Catalogs with `actions: {}` can omit it entirely.
+
+```typescript
+import { h } from "vue";
+import { defineRegistry } from "@json-render/vue";
+import { catalog } from "./catalog";
+
+export const { registry } = defineRegistry(catalog, {
+  components: {
+    Card: ({ props, children }) =>
+      h("div", { class: "card" }, [
+        h("h3", null, props.title),
+        props.description ? h("p", null, props.description) : null,
+        children,
+      ]),
+    Button: ({ props, emit }) =>
+      h("button", { onClick: () => emit("press") }, props.label),
+    Input: ({ props, bindings }) => {
+      // Use bindings?.value with a watcher to implement two-way binding
+      return h("label", null, [
+        props.label,
+        h("input", {
+          placeholder: props.placeholder ?? "",
+          value: props.value ?? "",
+        }),
+      ]);
+    },
+  },
+  // actions stubs are required when the catalog declares actions:
+  actions: {
+    submit: async () => {},
+    cancel: async () => {},
+  },
+});
+```
+
+> **Tip:** Use `useBoundProp(props.value, bindings?.value)` for two-way binding, or handle the `bindings` object directly in your component.
+
+### 3. Render Specs
+
+```vue
+<script setup lang="ts">
+import { StateProvider, ActionProvider, Renderer } from "@json-render/vue";
+import { registry } from "./registry";
+
+const spec = { /* ... */ };
+
+function handleSubmit(params) {
+  console.log("Submit", params);
+}
+</script>
+
+<template>
+  <StateProvider :initial-state="{ form: { name: '' } }">
+    <ActionProvider :handlers="{ submit: handleSubmit }">
+      <Renderer :spec="spec" :registry="registry" />
+    </ActionProvider>
+  </StateProvider>
+</template>
+```
+
+## Spec Format
+
+The Vue renderer uses the same flat element map format as the React renderer:
+
+```typescript
+interface Spec {
+  root: string;                          // Key of the root element
+  elements: Record<string, UIElement>;   // Flat map of elements by key
+  state?: Record<string, unknown>;       // Optional initial state
+}
+
+interface UIElement {
+  type: string;                          // Component name from catalog
+  props: Record<string, unknown>;        // Component props
+  children?: string[];                   // Keys of child elements
+  visible?: VisibilityCondition;         // Visibility condition
+}
+```
+
+Example spec:
+
+```json
+{
+  "root": "card-1",
+  "elements": {
+    "card-1": {
+      "type": "Card",
+      "props": { "title": "Welcome" },
+      "children": ["input-1", "btn-1"]
+    },
+    "input-1": {
+      "type": "Input",
+      "props": {
+        "value": { "$bindState": "/form/name" },
+        "label": "Name",
+        "placeholder": "Enter name"
+      }
+    },
+    "btn-1": {
+      "type": "Button",
+      "props": { "label": "Submit" },
+      "children": []
+    }
+  }
+}
+```
+
+## Providers
+
+### StateProvider
+
+Share data across components with JSON Pointer paths:
+
+```vue
+<StateProvider :initial-state="{ user: { name: 'John' } }">
+  <!-- children -->
+</StateProvider>
+```
+
+```typescript
+// In composables:
+const { state, get, set } = useStateStore();
+const name = get("/user/name");  // "John"
+set("/user/age", 25);
+
+// state is a ShallowRef<StateModel> — access with state.value
+console.log(state.value);
+```
+
+#### External Store (Controlled Mode)
+
+Pass a `StateStore` to bypass the internal state and wire json-render to any state management library (Pinia, VueUse, etc.):
+
+```typescript
+import { createStateStore, type StateStore } from "@json-render/vue";
+
+// Option 1: Use the built-in store outside of Vue
+const store = createStateStore({ count: 0 });
+```
+
+```vue
+<StateProvider :store="store">
+  <!-- children -->
+</StateProvider>
+```
+
+```typescript
+// Mutate from anywhere — Vue will re-render automatically:
+store.set("/count", 1);
+
+// Option 2: Implement the StateStore interface with your own backend
+const piniaStore: StateStore = {
+  get: (path) => getByPath(myStore.$state, path),
+  set: (path, value) => myStore.$patch(/* ... */),
+  update: (updates) => myStore.$patch(/* ... */),
+  getSnapshot: () => myStore.$state,
+  subscribe: (listener) => myStore.$subscribe(listener),
+};
+```
+
+When `store` is provided, `initialState` and `onStateChange` are ignored.
+
+### ActionProvider
+
+Handle actions from components:
+
+```vue
+<ActionProvider :handlers="{ submit: handleSubmit, cancel: handleCancel }">
+  <!-- children -->
+</ActionProvider>
+```
+
+### VisibilityProvider
+
+Control element visibility based on data:
+
+```vue
+<VisibilityProvider>
+  <!-- children -->
+</VisibilityProvider>
+```
+
+```json
+{
+  "type": "Alert",
+  "props": { "message": "Error!" },
+  "visible": { "$state": "/form/hasError" }
+}
+```
+
+### ValidationProvider
+
+Add field validation:
+
+```vue
+<ValidationProvider>
+  <!-- children -->
+</ValidationProvider>
+```
+
+```typescript
+// Use validation composable:
+const { errors, validate } = useFieldValidation("/form/email", {
+  checks: [
+    { type: "required", message: "Email required" },
+    { type: "email", message: "Invalid email" },
+  ],
+});
+```
+
+## Composables
+
+| Composable | Purpose |
+|------------|---------|
+| `useStateStore()` | Access state context (`state` as `ShallowRef`, `get`, `set`, `update`) |
+| `useStateValue(path)` | Get single value from state |
+| `useStateBinding(path)` | Two-way data binding (deprecated — use `$bindState` instead) |
+| `useIsVisible(condition)` | Check if a visibility condition is met |
+| `useActions()` | Access action context |
+| `useAction(binding)` | Get a single action dispatch function |
+| `useFieldValidation(path, config)` | Field validation state |
+
+> **Note:** `useStateStore().state` returns a `ShallowRef<StateModel>` — use `state.value` to access the underlying object. This differs from the React renderer where `state` is a plain object.
+
+## Visibility Conditions
+
+```typescript
+// Truthiness check
+{ "$state": "/user/isAdmin" }
+
+// Auth state (use state path)
+{ "$state": "/auth/isSignedIn" }
+
+// Comparisons (flat style)
+{ "$state": "/status", "eq": "active" }
+{ "$state": "/count", "gt": 10 }
+
+// Negation
+{ "$state": "/maintenance", "not": true }
+
+// Multiple conditions (implicit AND)
+[
+  { "$state": "/feature/enabled" },
+  { "$state": "/maintenance", "not": true }
+]
+
+// Always / never
+true   // always visible
+false  // never visible
+```
+
+TypeScript helpers from `@json-render/core`:
+
+```typescript
+import { visibility } from "@json-render/core";
+
+visibility.when("/path")       // { $state: "/path" }
+visibility.unless("/path")     // { $state: "/path", not: true }
+visibility.eq("/path", val)    // { $state: "/path", eq: val }
+visibility.neq("/path", val)   // { $state: "/path", neq: val }
+visibility.and(cond1, cond2)  // { $and: [cond1, cond2] }
+visibility.always             // true
+visibility.never              // false
+```
+
+## Dynamic Prop Expressions
+
+Any prop value can use data-driven expressions that resolve at render time. The renderer resolves these transparently before passing props to components.
+
+```json
+{
+  "type": "Badge",
+  "props": {
+    "label": { "$state": "/user/role" },
+    "color": {
+      "$cond": { "$state": "/user/role", "eq": "admin" },
+      "$then": "red",
+      "$else": "gray"
+    }
+  }
+}
+```
+
+For two-way binding, use `{ "$bindState": "/path" }` on the natural value prop. Inside repeat scopes, use `{ "$bindItem": "field" }` instead. Components receive resolved `bindings` with the state path for each bound prop.
+
+See [@json-render/core](../core/README.md) for full expression syntax.
+
+## Built-in Actions
+
+The `setState`, `pushState`, `removeState`, and `validateForm` actions are built into the Vue schema and handled automatically by `ActionProvider`. They are injected into AI prompts without needing to be declared in your catalog's `actions`. They update the state model, which triggers re-evaluation of visibility conditions and dynamic prop expressions:
+
+```json
+{
+  "type": "Button",
+  "props": { "label": "Switch Tab" },
+  "on": {
+    "press": {
+      "action": "setState",
+      "params": { "statePath": "/activeTab", "value": "settings" }
+    }
+  },
+  "children": []
+}
+```
+
+## Component Props
+
+When using `defineRegistry`, components receive these props via their render function:
+
+```typescript
+import type { VNode } from "vue";
+
+interface ComponentContext<P> {
+  props: P;                          // Typed props from the catalog (expressions resolved)
+  children?: VNode | VNode[];        // Rendered children (for container components)
+  emit: (event: string) => void;     // Emit a named event (always defined)
+  on: (event: string) => EventHandle; // Get event handle with metadata
+  loading?: boolean;                 // Whether the parent is loading
+  bindings?: Record<string, string>; // State paths for $bindState/$bindItem expressions
+}
+
+interface EventHandle {
+  emit: () => void;            // Fire the event
+  shouldPreventDefault: boolean; // Whether any binding requested preventDefault
+  bound: boolean;              // Whether any handler is bound
+}
+```
+
+Use `emit("press")` for simple event firing. Use `on("click")` when you need to check metadata like `shouldPreventDefault` or `bound`:
+
+```typescript
+Link: ({ props, on }) => {
+  const click = on("click");
+  return h("a", {
+    href: props.href,
+    onClick: (e: MouseEvent) => {
+      if (click.shouldPreventDefault) e.preventDefault();
+      click.emit();
+    },
+  }, props.label);
+},
+```
+
+### `BaseComponentProps`
+
+For building reusable component libraries that are not tied to a specific catalog, use the catalog-agnostic `BaseComponentProps` type:
+
+```typescript
+import type { BaseComponentProps } from "@json-render/vue";
+
+const Card = ({ props, children }: BaseComponentProps<{ title?: string }>) =>
+  h("div", null, [props.title, children]);
+```
+
+## Generate AI Prompts
+
+```typescript
+const systemPrompt = catalog.prompt();
+// Returns detailed prompt with component/action descriptions
+```
+
+## Full Example
+
+```typescript
+import { h } from "vue";
+import { defineCatalog } from "@json-render/core";
+import { schema } from "@json-render/vue/schema";
+import { defineRegistry, Renderer, StateProvider } from "@json-render/vue";
+import { z } from "zod";
+
+const catalog = defineCatalog(schema, {
+  components: {
+    Greeting: {
+      props: z.object({ name: z.string() }),
+      description: "Displays a greeting",
+    },
+  },
+  actions: {},
+});
+
+const { registry } = defineRegistry(catalog, {
+  components: {
+    Greeting: ({ props }) => h("h1", null, `Hello, ${props.name}!`),
+  },
+});
+
+const spec = {
+  root: "greeting-1",
+  elements: {
+    "greeting-1": {
+      type: "Greeting",
+      props: { name: "World" },
+      children: [],
+    },
+  },
+};
+
+// In your App.vue:
+// <StateProvider>
+//   <Renderer :spec="spec" :registry="registry" />
+// </StateProvider>
+```
+
+## Key Exports
+
+| Export | Purpose |
+|--------|---------|
+| `defineRegistry` | Create a type-safe component registry from a catalog |
+| `Renderer` | Render a spec using a registry |
+| `schema` | Element tree schema (includes built-in actions: `setState`, `pushState`, `removeState`) |
+| `useStateStore` | Access state context (`state` is `ShallowRef<StateModel>`) |
+| `useStateValue` | Get single value from state |
+| `useActions` | Access actions context |
+| `useAction` | Get a single action dispatch function |
+| `createStateStore` | Create a framework-agnostic in-memory `StateStore` |
+
+### Types
+
+| Export | Purpose |
+|--------|---------|
+| `ComponentContext` | Typed component render function context (catalog-aware) |
+| `BaseComponentProps` | Catalog-agnostic base type for reusable component libraries |
+| `EventHandle` | Event handle with `emit()`, `shouldPreventDefault`, `bound` |
+| `ActionProviderProps` | Props for `ActionProvider` |
+| `ValidationProviderProps` | Props for `ValidationProvider` |
+| `ComponentFn` | Component render function type |
+| `SetState` | State setter type |
+| `StateModel` | State model type |
+| `StateStore` | Interface for plugging in external state management |
+
+## Differences from `@json-render/react`
+
+| API | React | Vue | Note |
+|-----|-------|-----|------|
+| `useStateStore().state` | `StateModel` | `ShallowRef<StateModel>` | Vue reactivity; use `state.value` |
+| `children` type | `React.ReactNode` | `VNode \| VNode[]` | Platform-specific |
+| `useBoundProp` | exported | exported | Same API; returns `[value, setValue]` |
+| Streaming hooks | `useUIStream`, `useChatUI` | `useUIStream`, `useChatUI` | Same API; returns Vue `Ref` values |

packages/vue/package.json

@@ -0,0 +1,66 @@
+{
+  "name": "@json-render/vue",
+  "version": "0.9.1",
+  "license": "Apache-2.0",
+  "description": "Vue renderer for @json-render/core. JSON becomes Vue components.",
+  "keywords": [
+    "json",
+    "ui",
+    "vue",
+    "ai",
+    "generative-ui",
+    "llm",
+    "renderer",
+    "streaming",
+    "components"
+  ],
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/vercel-labs/json-render.git",
+    "directory": "packages/vue"
+  },
+  "homepage": "https://github.com/vercel-labs/json-render#readme",
+  "bugs": {
+    "url": "https://github.com/vercel-labs/json-render/issues"
+  },
+  "publishConfig": {
+    "access": "public"
+  },
+  "main": "./dist/index.js",
+  "module": "./dist/index.mjs",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.mjs",
+      "require": "./dist/index.js"
+    },
+    "./schema": {
+      "types": "./dist/schema.d.ts",
+      "import": "./dist/schema.mjs",
+      "require": "./dist/schema.js"
+    }
+  },
+  "files": [
+    "dist"
+  ],
+  "scripts": {
+    "build": "tsup",
+    "dev": "tsup --watch",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@json-render/core": "workspace:*"
+  },
+  "devDependencies": {
+    "@internal/typescript-config": "workspace:*",
+    "@vue/test-utils": "^2.4.6",
+    "tsup": "^8.0.2",
+    "typescript": "^5.4.5",
+    "vue": "^3.5.0"
+  },
+  "peerDependencies": {
+    "vue": "^3.5.0",
+    "zod": "^4.0.0"
+  }
+}

packages/vue/src/catalog-types.ts

@@ -0,0 +1,152 @@
+import type { VNode } from "vue";
+import type {
+  Catalog,
+  InferCatalogComponents,
+  InferCatalogActions,
+  InferComponentProps,
+  InferActionParams,
+  StateModel,
+} from "@json-render/core";
+
+export type { StateModel };
+
+// =============================================================================
+// State Types
+// =============================================================================
+
+/**
+ * State setter function for updating application state
+ */
+export type SetState = (
+  updater: (prev: Record<string, unknown>) => Record<string, unknown>,
+) => void;
+
+// =============================================================================
+// Component Types
+// =============================================================================
+
+/**
+ * Handle returned by the `on()` function for a specific event.
+ * Provides metadata about the event binding and a method to fire it.
+ *
+ * @example
+ * ```ts
+ * const press = on("press");
+ * if (press.shouldPreventDefault) e.preventDefault();
+ * press.emit();
+ * ```
+ */
+export interface EventHandle {
+  /** Fire the event (resolve action bindings) */
+  emit: () => void;
+  /** Whether any binding requested preventDefault */
+  shouldPreventDefault: boolean;
+  /** Whether any handler is bound to this event */
+  bound: boolean;
+}
+
+/**
+ * Catalog-agnostic base type for component render function arguments.
+ * Use this when building reusable component libraries that are not tied to a specific catalog.
+ *
+ * @example
+ * ```ts
+ * const Card = ({ props, children }: BaseComponentProps<{ title?: string }>) =>
+ *   h('div', null, [props.title, children])
+ * ```
+ */
+export interface BaseComponentProps<P = Record<string, unknown>> {
+  props: P;
+  /** Rendered children (from the default slot) */
+  children?: VNode | VNode[];
+  /** Simple event emitter (shorthand). Fires the event and returns void. */
+  emit: (event: string) => void;
+  /** Get an event handle with metadata. Use when you need shouldPreventDefault or bound checks. */
+  on: (event: string) => EventHandle;
+  /**
+   * Two-way binding paths resolved from `$bindState` / `$bindItem` expressions.
+   * Maps prop name → absolute state path for write-back.
+   */
+  bindings?: Record<string, string>;
+  loading?: boolean;
+}
+
+/**
+ * Context passed to component render functions
+ * @example
+ * const Button: ComponentFn<typeof catalog, 'Button'> = (ctx) => {
+ *   return h('button', { onClick: () => ctx.emit("press") }, ctx.props.label)
+ * }
+ */
+export interface ComponentContext<
+  C extends Catalog,
+  K extends keyof InferCatalogComponents<C>,
+> extends BaseComponentProps<InferComponentProps<C, K>> {}
+
+/**
+ * Component render function type for Vue
+ * @example
+ * const Button: ComponentFn<typeof catalog, 'Button'> = ({ props, emit }) =>
+ *   h('button', { onClick: () => emit("press") }, props.label)
+ */
+export type ComponentFn<
+  C extends Catalog,
+  K extends keyof InferCatalogComponents<C>,
+> = (ctx: ComponentContext<C, K>) => VNode | VNode[] | null | string;
+
+/**
+ * Registry of all component render functions for a catalog
+ * @example
+ * const components: Components<typeof myCatalog> = {
+ *   Button: ({ props }) => h('button', null, props.label),
+ *   Input: ({ props }) => h('input', { placeholder: props.placeholder }),
+ * };
+ */
+export type Components<C extends Catalog> = {
+  [K in keyof InferCatalogComponents<C>]: ComponentFn<C, K>;
+};
+
+// =============================================================================
+// Action Types
+// =============================================================================
+
+/**
+ * Action handler function type
+ * @example
+ * const viewCustomers: ActionFn<typeof catalog, 'viewCustomers'> = async (params, setState) => {
+ *   const data = await fetch('/api/customers');
+ *   setState(prev => ({ ...prev, customers: data }));
+ * };
+ */
+export type ActionFn<
+  C extends Catalog,
+  K extends keyof InferCatalogActions<C>,
+> = (
+  params: InferActionParams<C, K> | undefined,
+  setState: SetState,
+  state: StateModel,
+) => Promise<void>;
+
+/**
+ * Registry of all action handlers for a catalog
+ * @example
+ * const actions: Actions<typeof myCatalog> = {
+ *   viewCustomers: async (params, setState) => { ... },
+ *   createCustomer: async (params, setState) => { ... },
+ * };
+ */
+export type Actions<C extends Catalog> = {
+  [K in keyof InferCatalogActions<C>]: ActionFn<C, K>;
+};
+
+/**
+ * True when the catalog declares at least one action, false otherwise.
+ * Used by defineRegistry to conditionally require the `actions` field.
+ */
+export type CatalogHasActions<C extends Catalog> = [
+  InferCatalogActions<C>,
+] extends [never]
+  ? false
+  : [keyof InferCatalogActions<C>] extends [never]
+    ? false
+    : true;

packages/vue/src/composables/actions.test.ts

@@ -0,0 +1,106 @@
+import { describe, it, expect, vi } from "vitest";
+import { defineComponent, h, type Component } from "vue";
+import { mount } from "@vue/test-utils";
+import { StateProvider, useStateStore } from "./state";
+import { ActionProvider, useActions, useAction } from "./actions";
+
+/** Mount StateProvider → ActionProvider with a child that captures context. */
+function withProviders<T>(
+  composable: () => T,
+  handlers: Record<
+    string,
+    (params: Record<string, unknown>) => Promise<void>
+  > = {},
+  initialState: Record<string, unknown> = {},
+): { result: T } {
+  let result!: T;
+  const Child = defineComponent({
+    setup() {
+      result = composable();
+      return () => h("div");
+    },
+  });
+  mount(StateProvider as Component, {
+    props: { initialState } as any,
+    slots: {
+      default: () =>
+        h(ActionProvider as Component, { handlers } as any, {
+          default: () => h(Child),
+        }),
+    },
+  });
+  return { result };
+}
+
+describe("ActionProvider — provide/inject", () => {
+  it("useActions() throws outside a provider", () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    expect(() => useActions()).toThrow(
+      "useActions must be used within an ActionProvider",
+    );
+    warn.mockRestore();
+  });
+});
+
+describe("ActionProvider — custom handler dispatch", () => {
+  it("calling execute invokes the registered handler", async () => {
+    const handler = vi.fn().mockResolvedValue(undefined);
+    const { result } = withProviders(() => useActions(), { myAction: handler });
+    await result.execute({ action: "myAction", params: { x: 1 } });
+    expect(handler).toHaveBeenCalledOnce();
+  });
+
+  it("handler receives the resolved params", async () => {
+    const handler = vi.fn().mockResolvedValue(undefined);
+    const { result } = withProviders(() => useActions(), { myAction: handler });
+    await result.execute({ action: "myAction", params: { x: 1, y: "hello" } });
+    expect(handler).toHaveBeenCalledWith({ x: 1, y: "hello" });
+  });
+
+  it("console.warn is called for unknown actions", async () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    const { result } = withProviders(() => useActions());
+    await result.execute({ action: "unknownAction" });
+    expect(warn).toHaveBeenCalledWith(expect.stringContaining("unknownAction"));
+    warn.mockRestore();
+  });
+});
+
+describe("ActionProvider — built-in setState integration", () => {
+  it("executing setState updates state via the provider chain", async () => {
+    let stateCtx!: ReturnType<typeof useStateStore>;
+    let actionsCtx!: ReturnType<typeof useActions>;
+
+    const Child = defineComponent({
+      setup() {
+        stateCtx = useStateStore();
+        actionsCtx = useActions();
+        return () => h("div");
+      },
+    });
+
+    mount(StateProvider as Component, {
+      props: { initialState: { v: 0 } } as any,
+      slots: {
+        default: () =>
+          h(ActionProvider as Component, null, {
+            default: () => h(Child),
+          }),
+      },
+    });
+
+    await actionsCtx.execute({
+      action: "setState",
+      params: { statePath: "/v", value: 42 },
+    });
+    expect(stateCtx.state.value).toEqual({ v: 42 });
+  });
+});
+
+describe("useAction", () => {
+  it("returns { execute, isLoading: false } before execution", () => {
+    const { result } = withProviders(() => useAction({ action: "myAction" }));
+    expect(typeof result.execute).toBe("function");
+    expect(result.isLoading.value).toBe(false);
+  });
+});

packages/vue/src/composables/actions.ts

@@ -0,0 +1,487 @@
+import {
+  computed,
+  defineComponent,
+  h,
+  inject,
+  provide,
+  ref,
+  watch,
+  type ComputedRef,
+  type PropType,
+} from "vue";
+import {
+  resolveAction,
+  executeAction,
+  type ActionBinding,
+  type ActionHandler,
+  type ActionConfirm,
+  type ResolvedAction,
+} from "@json-render/core";
+import { useStateStore } from "./state";
+import { useOptionalValidation } from "./validation";
+
+/**
+ * Generate a unique ID for use with the "$id" token.
+ */
+let idCounter = 0;
+function generateUniqueId(): string {
+  idCounter += 1;
+  return `${Date.now()}-${idCounter}`;
+}
+
+/**
+ * Deep-resolve dynamic value references within an object.
+ *
+ * Supported tokens:
+ * - `{ $state: "/statePath" }` - read a value from state
+ * - `"$id"` (string) or `{ "$id": true }` - generate a unique ID
+ */
+function deepResolveValue(
+  value: unknown,
+  get: (path: string) => unknown,
+): unknown {
+  if (value === null || value === undefined) return value;
+
+  if (value === "$id") {
+    return generateUniqueId();
+  }
+
+  if (typeof value === "object" && !Array.isArray(value)) {
+    const obj = value as Record<string, unknown>;
+    const keys = Object.keys(obj);
+
+    if (keys.length === 1 && typeof obj.$state === "string") {
+      return get(obj.$state as string);
+    }
+
+    if (keys.length === 1 && "$id" in obj) {
+      return generateUniqueId();
+    }
+  }
+
+  if (Array.isArray(value)) {
+    return value.map((item) => deepResolveValue(item, get));
+  }
+
+  if (typeof value === "object") {
+    const resolved: Record<string, unknown> = {};
+    for (const [key, val] of Object.entries(value as Record<string, unknown>)) {
+      resolved[key] = deepResolveValue(val, get);
+    }
+    return resolved;
+  }
+
+  return value;
+}
+
+/**
+ * Pending confirmation state
+ */
+export interface PendingConfirmation {
+  action: ResolvedAction;
+  handler: ActionHandler;
+  resolve: () => void;
+  reject: () => void;
+}
+
+/**
+ * Action context value
+ */
+export interface ActionContextValue {
+  handlers: Record<string, ActionHandler>;
+  loadingActions: Set<string>;
+  pendingConfirmation: PendingConfirmation | null;
+  execute: (binding: ActionBinding) => Promise<void>;
+  confirm: () => void;
+  cancel: () => void;
+  registerHandler: (name: string, handler: ActionHandler) => void;
+}
+
+const ACTIONS_KEY = Symbol("json-render:actions");
+
+export interface ActionProviderProps {
+  handlers?: Record<string, ActionHandler>;
+  navigate?: (path: string) => void;
+}
+
+/**
+ * Provider for action execution
+ */
+export const ActionProvider = defineComponent({
+  name: "ActionProvider",
+  props: {
+    handlers: {
+      type: Object as PropType<Record<string, ActionHandler>>,
+      default: () => ({}),
+    },
+    navigate: {
+      type: Function as PropType<(path: string) => void>,
+      default: undefined,
+    },
+  },
+  setup(props, { slots }) {
+    const { get, set, getSnapshot } = useStateStore();
+    const validation = useOptionalValidation();
+
+    const handlers = ref<Record<string, ActionHandler>>(props.handlers ?? {});
+    const loadingActions = ref<Set<string>>(new Set());
+    const pendingConfirmation = ref<PendingConfirmation | null>(null);
+
+    // Sync handlers when prop changes
+    watch(
+      () => props.handlers,
+      (newHandlers) => {
+        if (newHandlers) handlers.value = newHandlers;
+      },
+    );
+
+    const registerHandler = (name: string, handler: ActionHandler) => {
+      handlers.value = { ...handlers.value, [name]: handler };
+    };
+
+    const execute = async (binding: ActionBinding): Promise<void> => {
+      const resolved = resolveAction(binding, getSnapshot());
+
+      // Built-in: setState
+      if (resolved.action === "setState" && resolved.params) {
+        const statePath = resolved.params.statePath as string;
+        const value = resolved.params.value;
+        if (statePath) {
+          set(statePath, value);
+        }
+        return;
+      }
+
+      // Built-in: pushState
+      if (resolved.action === "pushState" && resolved.params) {
+        const statePath = resolved.params.statePath as string;
+        const rawValue = resolved.params.value;
+        if (statePath) {
+          const resolvedValue = deepResolveValue(rawValue, get);
+          const arr = (get(statePath) as unknown[] | undefined) ?? [];
+          set(statePath, [...arr, resolvedValue]);
+          const clearStatePath = resolved.params.clearStatePath as
+            | string
+            | undefined;
+          if (clearStatePath) {
+            set(clearStatePath, "");
+          }
+        }
+        return;
+      }
+
+      // Built-in: removeState
+      if (resolved.action === "removeState" && resolved.params) {
+        const statePath = resolved.params.statePath as string;
+        const index = resolved.params.index as number;
+        if (statePath !== undefined && index !== undefined) {
+          const arr = (get(statePath) as unknown[] | undefined) ?? [];
+          set(
+            statePath,
+            arr.filter((_, i) => i !== index),
+          );
+        }
+        return;
+      }
+
+      // Built-in: validateForm — triggers validateAll and writes result to state
+      if (resolved.action === "validateForm") {
+        const validateAll = validation?.validateAll;
+        if (!validateAll) {
+          console.warn(
+            "validateForm action was dispatched but no ValidationProvider is connected. " +
+              "Ensure ValidationProvider is rendered inside the provider tree.",
+          );
+          return;
+        }
+        const valid = validateAll();
+        const errors: Record<string, string[]> = {};
+        for (const [path, fs] of Object.entries(validation.fieldStates)) {
+          if (fs.result && !fs.result.valid) {
+            errors[path] = fs.result.errors;
+          }
+        }
+        const statePath =
+          (resolved.params?.statePath as string) || "/formValidation";
+        set(statePath, { valid, errors });
+        return;
+      }
+
+      // Built-in: push (navigation)
+      if (resolved.action === "push" && resolved.params) {
+        const screen = resolved.params.screen as string;
+        if (screen) {
+          const currentScreen = get("/currentScreen") as string | undefined;
+          const navStack = (get("/navStack") as string[] | undefined) ?? [];
+          if (currentScreen) {
+            set("/navStack", [...navStack, currentScreen]);
+          } else {
+            set("/navStack", [...navStack, ""]);
+          }
+          set("/currentScreen", screen);
+        }
+        return;
+      }
+
+      // Built-in: pop (navigation)
+      if (resolved.action === "pop") {
+        const navStack = (get("/navStack") as string[] | undefined) ?? [];
+        if (navStack.length > 0) {
+          const previousScreen = navStack[navStack.length - 1];
+          set("/navStack", navStack.slice(0, -1));
+          if (previousScreen) {
+            set("/currentScreen", previousScreen);
+          } else {
+            set("/currentScreen", undefined);
+          }
+        }
+        return;
+      }
+
+      const handler = handlers.value[resolved.action];
+
+      if (!handler) {
+        console.warn(`No handler registered for action: ${resolved.action}`);
+        return;
+      }
+
+      // If confirmation is required, show dialog first
+      if (resolved.confirm) {
+        await new Promise<void>((resolve, reject) => {
+          pendingConfirmation.value = {
+            action: resolved,
+            handler,
+            resolve: () => {
+              pendingConfirmation.value = null;
+              resolve();
+            },
+            reject: () => {
+              pendingConfirmation.value = null;
+              reject(new Error("Action cancelled"));
+            },
+          };
+        });
+
+        const addLoading = new Set(loadingActions.value);
+        addLoading.add(resolved.action);
+        loadingActions.value = addLoading;
+        try {
+          await executeAction({
+            action: resolved,
+            handler,
+            setState: set,
+            navigate: props.navigate,
+            executeAction: async (name) => {
+              const subBinding: ActionBinding = { action: name };
+              await execute(subBinding);
+            },
+          });
+        } finally {
+          const removeLoading = new Set(loadingActions.value);
+          removeLoading.delete(resolved.action);
+          loadingActions.value = removeLoading;
+        }
+        return;
+      }
+
+      // Execute immediately
+      const addLoading = new Set(loadingActions.value);
+      addLoading.add(resolved.action);
+      loadingActions.value = addLoading;
+      try {
+        await executeAction({
+          action: resolved,
+          handler,
+          setState: set,
+          navigate: props.navigate,
+          executeAction: async (name) => {
+            const subBinding: ActionBinding = { action: name };
+            await execute(subBinding);
+          },
+        });
+      } finally {
+        const removeLoading = new Set(loadingActions.value);
+        removeLoading.delete(resolved.action);
+        loadingActions.value = removeLoading;
+      }
+    };
+
+    const confirm = () => pendingConfirmation.value?.resolve();
+    const cancel = () => pendingConfirmation.value?.reject();
+
+    provide<ActionContextValue>(ACTIONS_KEY, {
+      get handlers() {
+        return handlers.value;
+      },
+      get loadingActions() {
+        return loadingActions.value;
+      },
+      get pendingConfirmation() {
+        return pendingConfirmation.value;
+      },
+      execute,
+      confirm,
+      cancel,
+      registerHandler,
+    });
+
+    return () => slots.default?.();
+  },
+});
+
+/**
+ * Composable to access action context
+ */
+export function useActions(): ActionContextValue {
+  const ctx = inject<ActionContextValue>(ACTIONS_KEY);
+  if (!ctx) {
+    throw new Error("useActions must be used within an ActionProvider");
+  }
+  return ctx;
+}
+
+/**
+ * Composable to execute an action binding
+ */
+export function useAction(binding: ActionBinding): {
+  execute: () => Promise<void>;
+  isLoading: ComputedRef<boolean>;
+} {
+  const ctx = useActions();
+  return {
+    execute: () => ctx.execute(binding),
+    isLoading: computed(() => ctx.loadingActions.has(binding.action)),
+  };
+}
+
+// =============================================================================
+// ConfirmDialog component
+// =============================================================================
+
+/**
+ * Props for ConfirmDialog component
+ */
+export interface ConfirmDialogProps {
+  confirm: ActionConfirm;
+  onConfirm: () => void;
+  onCancel: () => void;
+}
+
+/**
+ * Default confirmation dialog component
+ */
+export const ConfirmDialog = defineComponent({
+  name: "ConfirmDialog",
+  props: {
+    confirm: {
+      type: Object as PropType<ActionConfirm>,
+      required: true,
+    },
+    onConfirm: {
+      type: Function as PropType<() => void>,
+      required: true,
+    },
+    onCancel: {
+      type: Function as PropType<() => void>,
+      required: true,
+    },
+  },
+  setup(props) {
+    return () => {
+      const isDanger = props.confirm.variant === "danger";
+
+      return h(
+        "div",
+        {
+          style: {
+            position: "fixed",
+            inset: "0",
+            backgroundColor: "rgba(0, 0, 0, 0.5)",
+            display: "flex",
+            alignItems: "center",
+            justifyContent: "center",
+            zIndex: "50",
+          },
+          onClick: props.onCancel,
+        },
+        [
+          h(
+            "div",
+            {
+              style: {
+                backgroundColor: "white",
+                borderRadius: "8px",
+                padding: "24px",
+                maxWidth: "400px",
+                width: "100%",
+                boxShadow: "0 20px 25px -5px rgba(0, 0, 0, 0.1)",
+              },
+              onClick: (e: MouseEvent) => e.stopPropagation(),
+            },
+            [
+              h(
+                "h3",
+                {
+                  style: {
+                    margin: "0 0 8px 0",
+                    fontSize: "18px",
+                    fontWeight: "600",
+                  },
+                },
+                props.confirm.title,
+              ),
+              h(
+                "p",
+                {
+                  style: { margin: "0 0 24px 0", color: "#6b7280" },
+                },
+                props.confirm.message,
+              ),
+              h(
+                "div",
+                {
+                  style: {
+                    display: "flex",
+                    gap: "12px",
+                    justifyContent: "flex-end",
+                  },
+                },
+                [
+                  h(
+                    "button",
+                    {
+                      style: {
+                        padding: "8px 16px",
+                        borderRadius: "6px",
+                        border: "1px solid #d1d5db",
+                        backgroundColor: "white",
+                        cursor: "pointer",
+                      },
+                      onClick: props.onCancel,
+                    },
+                    props.confirm.cancelLabel ?? "Cancel",
+                  ),
+                  h(
+                    "button",
+                    {
+                      style: {
+                        padding: "8px 16px",
+                        borderRadius: "6px",
+                        border: "none",
+                        backgroundColor: isDanger ? "#dc2626" : "#3b82f6",
+                        color: "white",
+                        cursor: "pointer",
+                      },
+                      onClick: props.onConfirm,
+                    },
+                    props.confirm.confirmLabel ?? "Confirm",
+                  ),
+                ],
+              ),
+            ],
+          ),
+        ],
+      );
+    };
+  },
+});

packages/vue/src/composables/repeat-scope.ts

@@ -0,0 +1,51 @@
+import { defineComponent, inject, provide, type PropType } from "vue";
+
+/**
+ * Repeat scope value provided to child elements inside a repeated element.
+ */
+export interface RepeatScopeValue {
+  /** The current array item object */
+  item: unknown;
+  /** Index of the current item in the array */
+  index: number;
+  /** Absolute state path to the current array item (e.g. "/todos/0") — used for statePath two-way binding */
+  basePath: string;
+}
+
+const REPEAT_SCOPE_KEY = Symbol("json-render:repeat-scope");
+
+/**
+ * Provides repeat scope to child elements so $item and $index expressions resolve correctly.
+ */
+export const RepeatScopeProvider = defineComponent({
+  name: "RepeatScopeProvider",
+  props: {
+    item: {
+      required: true,
+    },
+    index: {
+      type: Number,
+      required: true,
+    },
+    basePath: {
+      type: String as PropType<string>,
+      required: true,
+    },
+  },
+  setup(props, { slots }) {
+    provide(REPEAT_SCOPE_KEY, props as RepeatScopeValue);
+    return () => slots.default?.();
+  },
+});
+
+/**
+ * Read the current repeat scope (or null if not inside a repeated element).
+ */
+export function useRepeatScope(): RepeatScopeValue | null {
+  return (
+    inject<RepeatScopeValue>(
+      REPEAT_SCOPE_KEY,
+      null as unknown as RepeatScopeValue,
+    ) ?? null
+  );
+}

packages/vue/src/composables/state.test.ts

@@ -0,0 +1,139 @@
+import { describe, it, expect, vi } from "vitest";
+import { defineComponent, h, type Component } from "vue";
+import { mount } from "@vue/test-utils";
+import { createStateStore } from "@json-render/core";
+import { StateProvider, useStateStore } from "./state";
+
+/** Mount a StateProvider with a child that captures the injected context. */
+function withProvider<T>(
+  composable: () => T,
+  props: Record<string, unknown> = {},
+): { result: T } {
+  let result!: T;
+  const Child = defineComponent({
+    setup() {
+      result = composable();
+      return () => h("div");
+    },
+  });
+  mount(StateProvider as Component, {
+    props: props as any,
+    slots: { default: () => h(Child) },
+  });
+  return { result };
+}
+
+describe("StateProvider — provide/inject", () => {
+  it("useStateStore() throws outside a provider", () => {
+    // inject() returns undefined outside of component setup; our guard throws
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    expect(() => useStateStore()).toThrow(
+      "useStateStore must be used within a StateProvider",
+    );
+    warn.mockRestore();
+  });
+
+  it("child receives the context from StateProvider", () => {
+    const { result } = withProvider(() => useStateStore());
+    expect(result).toBeDefined();
+    expect(result.state).toBeDefined();
+    expect(typeof result.get).toBe("function");
+    expect(typeof result.set).toBe("function");
+    expect(typeof result.update).toBe("function");
+  });
+
+  it("state.value is a plain object (not a wrapper type)", () => {
+    const { result } = withProvider(() => useStateStore(), {
+      initialState: { x: 1 },
+    });
+    expect(result.state.value).toEqual({ x: 1 });
+    // Should be a plain object, not a Vue Proxy of a ShallowRef wrapper
+    expect(typeof result.state.value).toBe("object");
+  });
+});
+
+describe("StateProvider (uncontrolled) — reactivity", () => {
+  it("state.value reflects initialState on mount", () => {
+    const { result } = withProvider(() => useStateStore(), {
+      initialState: { count: 5 },
+    });
+    expect(result.state.value).toEqual({ count: 5 });
+  });
+
+  it("after set(), state.value is updated synchronously", () => {
+    const { result } = withProvider(() => useStateStore(), {
+      initialState: { x: 0 },
+    });
+    result.set("/x", 42);
+    expect(result.state.value).toEqual({ x: 42 });
+  });
+
+  it("after update(), all paths are reflected in state.value", () => {
+    const { result } = withProvider(() => useStateStore(), {
+      initialState: {},
+    });
+    result.update({ "/a": 1, "/b": "hello" });
+    expect(result.state.value).toEqual({ a: 1, b: "hello" });
+  });
+
+  it("onStateChange is fired with the changes array on set", () => {
+    const onChange = vi.fn();
+    const { result } = withProvider(() => useStateStore(), {
+      initialState: {},
+      onStateChange: onChange,
+    });
+    result.set("/name", "Alice");
+    expect(onChange).toHaveBeenCalledOnce();
+    expect(onChange).toHaveBeenCalledWith([{ path: "/name", value: "Alice" }]);
+  });
+
+  it("onStateChange is fired once with all changed entries on update", () => {
+    const onChange = vi.fn();
+    const { result } = withProvider(() => useStateStore(), {
+      initialState: {},
+      onStateChange: onChange,
+    });
+    result.update({ "/a": 1, "/b": 2 });
+    expect(onChange).toHaveBeenCalledOnce();
+    const [changes] = onChange.mock.calls[0]!;
+    expect(changes).toEqual(
+      expect.arrayContaining([
+        { path: "/a", value: 1 },
+        { path: "/b", value: 2 },
+      ]),
+    );
+  });
+});
+
+describe("StateProvider (controlled mode)", () => {
+  it("state.value reads from the external store snapshot", () => {
+    const store = createStateStore({ x: 10 });
+    const { result } = withProvider(() => useStateStore(), { store });
+    expect(result.state.value).toEqual({ x: 10 });
+  });
+
+  it("set() writes through to the external store", () => {
+    const store = createStateStore({ x: 0 });
+    const { result } = withProvider(() => useStateStore(), { store });
+    result.set("/x", 99);
+    expect(store.getSnapshot()).toEqual({ x: 99 });
+  });
+
+  it("external store mutation triggers state.value update", () => {
+    const store = createStateStore({ x: 0 });
+    const { result } = withProvider(() => useStateStore(), { store });
+    store.set("/x", 99);
+    expect(result.state.value).toEqual({ x: 99 });
+  });
+
+  it("onStateChange is NOT called in controlled mode", () => {
+    const store = createStateStore({ x: 0 });
+    const onChange = vi.fn();
+    const { result } = withProvider(() => useStateStore(), {
+      store,
+      onStateChange: onChange,
+    });
+    result.set("/x", 99);
+    expect(onChange).not.toHaveBeenCalled();
+  });
+});

packages/vue/src/composables/state.ts

@@ -0,0 +1,216 @@
+import {
+  computed,
+  defineComponent,
+  inject,
+  onUnmounted,
+  provide,
+  ref,
+  shallowRef,
+  watch,
+  type ComputedRef,
+  type PropType,
+  type ShallowRef,
+} from "vue";
+import {
+  createStateStore,
+  getByPath,
+  type StateModel,
+  type StateStore,
+} from "@json-render/core";
+import { flattenToPointers } from "@json-render/core/store-utils";
+
+/**
+ * State context value
+ */
+export interface StateContextValue {
+  /** Reactive state snapshot — use state.value in reactive contexts */
+  state: ShallowRef<StateModel>;
+  /** Get a value by path */
+  get: (path: string) => unknown;
+  /** Set a value by path */
+  set: (path: string, value: unknown) => void;
+  /** Update multiple values at once */
+  update: (updates: Record<string, unknown>) => void;
+  /** Return the live state snapshot from the underlying store (not through Vue reactivity). */
+  getSnapshot: () => StateModel;
+}
+
+const STATE_KEY = Symbol("json-render:state");
+
+/**
+ * Props for StateProvider
+ */
+export interface StateProviderProps {
+  /**
+   * External store that owns the state. When provided, the provider operates
+   * in **controlled mode** — `initialState` and `onStateChange` are ignored
+   * and the store is the single source of truth.
+   */
+  store?: StateStore;
+  /** Initial state model (used only in uncontrolled mode) */
+  initialState?: StateModel;
+  /**
+   * Callback when state changes (used only in uncontrolled mode).
+   * Called once per `set` or `update` with all changed entries.
+   */
+  onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
+}
+
+/**
+ * Provider for state model context.
+ *
+ * Supports two modes:
+ * - **Controlled**: pass a `store` prop (e.g. backed by Redux / Zustand).
+ * - **Uncontrolled** (default): omit `store` and optionally pass
+ *   `initialState` / `onStateChange`.
+ */
+export const StateProvider = defineComponent({
+  name: "StateProvider",
+  props: {
+    store: {
+      type: Object as PropType<StateStore>,
+      default: undefined,
+    },
+    initialState: {
+      type: Object as PropType<StateModel>,
+      default: undefined,
+    },
+    onStateChange: {
+      type: Function as PropType<
+        (changes: Array<{ path: string; value: unknown }>) => void
+      >,
+      default: undefined,
+    },
+  },
+  setup(props, { slots }) {
+    const isControlled = !!props.store;
+
+    // Use external store (controlled) or create internal store (uncontrolled)
+    const internalStore = !isControlled
+      ? createStateStore(props.initialState ?? {})
+      : null;
+    const store: StateStore = props.store ?? internalStore!;
+
+    const state = shallowRef<StateModel>(store.getSnapshot());
+
+    const unsubscribe = store.subscribe(() => {
+      state.value = store.getSnapshot();
+    });
+    onUnmounted(unsubscribe);
+
+    // Sync external initialState changes (uncontrolled mode only)
+    if (!isControlled) {
+      let prevFlat: Record<string, unknown> =
+        props.initialState && Object.keys(props.initialState).length > 0
+          ? flattenToPointers(props.initialState)
+          : {};
+
+      watch(
+        () => props.initialState,
+        (newInitialState) => {
+          if (!newInitialState) return;
+          const nextFlat =
+            Object.keys(newInitialState).length > 0
+              ? flattenToPointers(newInitialState)
+              : {};
+          const allKeys = new Set([
+            ...Object.keys(prevFlat),
+            ...Object.keys(nextFlat),
+          ]);
+          const updates: Record<string, unknown> = {};
+          for (const key of allKeys) {
+            if (prevFlat[key] !== nextFlat[key]) {
+              updates[key] = key in nextFlat ? nextFlat[key] : undefined;
+            }
+          }
+          prevFlat = nextFlat;
+          if (Object.keys(updates).length > 0) {
+            store.update(updates);
+          }
+        },
+      );
+    }
+
+    // Keep onStateChange in a ref so it always reads the latest callback
+    const onStateChangeRef = ref(props.onStateChange);
+    watch(
+      () => props.onStateChange,
+      (fn) => {
+        onStateChangeRef.value = fn;
+      },
+    );
+
+    const get = (path: string) => store.get(path);
+    const getSnapshot = () => store.getSnapshot();
+
+    const set = (path: string, value: unknown) => {
+      const prev = store.getSnapshot();
+      store.set(path, value);
+      if (!isControlled && store.getSnapshot() !== prev) {
+        onStateChangeRef.value?.([{ path, value }]);
+      }
+    };
+
+    const update = (updates: Record<string, unknown>) => {
+      const prev = store.getSnapshot();
+      store.update(updates);
+      if (!isControlled && store.getSnapshot() !== prev) {
+        const changes: Array<{ path: string; value: unknown }> = [];
+        for (const [path, value] of Object.entries(updates)) {
+          if (getByPath(prev, path) !== value) {
+            changes.push({ path, value });
+          }
+        }
+        if (changes.length > 0) {
+          onStateChangeRef.value?.(changes);
+        }
+      }
+    };
+
+    provide<StateContextValue>(STATE_KEY, {
+      state,
+      get,
+      set,
+      update,
+      getSnapshot,
+    });
+
+    return () => slots.default?.();
+  },
+});
+
+/**
+ * Composable to access the state context
+ */
+export function useStateStore(): StateContextValue {
+  const ctx = inject<StateContextValue>(STATE_KEY);
+  if (!ctx) {
+    throw new Error("useStateStore must be used within a StateProvider");
+  }
+  return ctx;
+}
+
+/**
+ * Composable to get a value from the state model (reactive)
+ */
+export function useStateValue<T>(path: string): ComputedRef<T | undefined> {
+  const { state } = useStateStore();
+  return computed(() => getByPath(state.value, path) as T | undefined);
+}
+
+/**
+ * Composable to get and set a value from the state model by path.
+ *
+ * This is the path-based variant for use in arbitrary composables. For
+ * registry components that receive `bindings` from the renderer, prefer
+ * `useBoundProp` which reads the already-resolved prop value and writes back
+ * to the bound path.
+ */
+export function useStateBinding<T>(
+  path: string,
+): [ComputedRef<T | undefined>, (value: T) => void] {
+  const { state, set } = useStateStore();
+  const value = computed(() => getByPath(state.value, path) as T | undefined);
+  const setValue = (newValue: T) => set(path, newValue);
+  return [value, setValue];
+}

packages/vue/src/composables/validation.test.ts

@@ -0,0 +1,209 @@
+import { describe, it, expect, vi } from "vitest";
+import { defineComponent, h, type Component } from "vue";
+import { mount } from "@vue/test-utils";
+import { StateProvider } from "./state";
+import {
+  ValidationProvider,
+  useOptionalValidation,
+  useValidation,
+  useFieldValidation,
+} from "./validation";
+
+/** Mount StateProvider → ValidationProvider with a child that captures context. */
+function withProviders<T>(
+  composable: () => T,
+  initialState: Record<string, unknown> = {},
+): { result: T } {
+  let result!: T;
+  const Child = defineComponent({
+    setup() {
+      result = composable();
+      return () => h("div");
+    },
+  });
+  mount(StateProvider as Component, {
+    props: { initialState } as any,
+    slots: {
+      default: () =>
+        h(ValidationProvider as Component, null, {
+          default: () => h(Child),
+        }),
+    },
+  });
+  return { result };
+}
+
+/** Mount only inside StateProvider (no ValidationProvider) */
+function withStateOnly<T>(composable: () => T): { result: T } {
+  let result!: T;
+  const Child = defineComponent({
+    setup() {
+      result = composable();
+      return () => h("div");
+    },
+  });
+  mount(StateProvider as Component, {
+    props: { initialState: {} } as any,
+    slots: { default: () => h(Child) },
+  });
+  return { result };
+}
+
+describe("ValidationProvider — provide/inject", () => {
+  it("useValidation() throws outside a provider", () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    expect(() => useValidation()).toThrow(
+      "useValidation must be used within a ValidationProvider",
+    );
+    warn.mockRestore();
+  });
+});
+
+describe("useOptionalValidation", () => {
+  it("returns null outside a ValidationProvider", () => {
+    const { result } = withStateOnly(() => useOptionalValidation());
+    expect(result).toBeNull();
+  });
+
+  it("returns context inside a ValidationProvider", () => {
+    const { result } = withProviders(() => useOptionalValidation());
+    expect(result).not.toBeNull();
+    expect(typeof result!.validate).toBe("function");
+    expect(typeof result!.validateAll).toBe("function");
+  });
+});
+
+describe("useFieldValidation — lifecycle", () => {
+  it("after validate(), isValid and errors reflect the result", () => {
+    const { result } = withProviders(
+      () =>
+        useFieldValidation("/name", {
+          checks: [{ type: "required", message: "Name is required" }],
+        }),
+      { name: "" },
+    );
+    const validationResult = result.validate();
+    expect(validationResult.valid).toBe(false);
+    expect(validationResult.errors).toContain("Name is required");
+  });
+
+  it("after validate() with valid value, isValid is true", () => {
+    const { result } = withProviders(
+      () =>
+        useFieldValidation("/name", {
+          checks: [{ type: "required", message: "Name is required" }],
+        }),
+      { name: "Alice" },
+    );
+    const validationResult = result.validate();
+    expect(validationResult.valid).toBe(true);
+    expect(validationResult.errors).toHaveLength(0);
+  });
+
+  it("touch() sets touched: true in the validation context", () => {
+    let validationCtx!: ReturnType<typeof useValidation>;
+    let fieldCtx!: ReturnType<typeof useFieldValidation>;
+
+    const Child = defineComponent({
+      setup() {
+        validationCtx = useValidation();
+        fieldCtx = useFieldValidation("/email");
+        return () => h("div");
+      },
+    });
+
+    mount(StateProvider as Component, {
+      props: { initialState: {} } as any,
+      slots: {
+        default: () =>
+          h(ValidationProvider as Component, null, {
+            default: () => h(Child),
+          }),
+      },
+    });
+
+    fieldCtx.touch();
+    expect(validationCtx.fieldStates["/email"]?.touched).toBe(true);
+  });
+
+  it("clear() resets the field state from the validation context", () => {
+    let validationCtx!: ReturnType<typeof useValidation>;
+    let fieldCtx!: ReturnType<typeof useFieldValidation>;
+
+    const Child = defineComponent({
+      setup() {
+        validationCtx = useValidation();
+        fieldCtx = useFieldValidation("/email", {
+          checks: [{ type: "required", message: "Required" }],
+        });
+        return () => h("div");
+      },
+    });
+
+    mount(StateProvider as Component, {
+      props: { initialState: { email: "" } } as any,
+      slots: {
+        default: () =>
+          h(ValidationProvider as Component, null, {
+            default: () => h(Child),
+          }),
+      },
+    });
+
+    fieldCtx.validate(); // populate fieldStates
+    fieldCtx.clear();
+    expect(validationCtx.fieldStates["/email"]).toBeUndefined();
+  });
+
+  it("validateAll() returns true when all registered fields pass", () => {
+    let validationCtx!: ReturnType<typeof useValidation>;
+
+    const Child = defineComponent({
+      setup() {
+        validationCtx = useValidation();
+        useFieldValidation("/name", {
+          checks: [{ type: "required", message: "Required" }],
+        });
+        return () => h("div");
+      },
+    });
+
+    mount(StateProvider as Component, {
+      props: { initialState: { name: "Alice" } } as any,
+      slots: {
+        default: () =>
+          h(ValidationProvider as Component, null, {
+            default: () => h(Child),
+          }),
+      },
+    });
+
+    expect(validationCtx.validateAll()).toBe(true);
+  });
+
+  it("validateAll() returns false when any field fails", () => {
+    let validationCtx!: ReturnType<typeof useValidation>;
+
+    const Child = defineComponent({
+      setup() {
+        validationCtx = useValidation();
+        useFieldValidation("/name", {
+          checks: [{ type: "required", message: "Required" }],
+        });
+        return () => h("div");
+      },
+    });
+
+    mount(StateProvider as Component, {
+      props: { initialState: { name: "" } } as any,
+      slots: {
+        default: () =>
+          h(ValidationProvider as Component, null, {
+            default: () => h(Child),
+          }),
+      },
+    });
+
+    expect(validationCtx.validateAll()).toBe(false);
+  });
+});

packages/vue/src/composables/validation.ts

@@ -0,0 +1,267 @@
+import {
+  computed,
+  defineComponent,
+  inject,
+  onMounted,
+  onUnmounted,
+  provide,
+  ref,
+  type ComputedRef,
+  type PropType,
+} from "vue";
+import {
+  runValidation,
+  type ValidationConfig,
+  type ValidationFunction,
+  type ValidationResult,
+} from "@json-render/core";
+import { useStateStore } from "./state";
+
+/**
+ * Field validation state
+ */
+export interface FieldValidationState {
+  touched: boolean;
+  validated: boolean;
+  result: ValidationResult | null;
+}
+
+/**
+ * Validation context value
+ */
+export interface ValidationContextValue {
+  customFunctions: Record<string, ValidationFunction>;
+  fieldStates: Record<string, FieldValidationState>;
+  validate: (path: string, config: ValidationConfig) => ValidationResult;
+  touch: (path: string) => void;
+  clear: (path: string) => void;
+  validateAll: () => boolean;
+  registerField: (path: string, config: ValidationConfig) => void;
+}
+
+const VALIDATION_KEY = Symbol("json-render:validation");
+
+export interface ValidationProviderProps {
+  customFunctions?: Record<string, ValidationFunction>;
+}
+
+/**
+ * Compare two args records shallowly.
+ */
+function dynamicArgsEqual(
+  a: Record<string, unknown> | undefined,
+  b: Record<string, unknown> | undefined,
+): boolean {
+  if (a === b) return true;
+  if (!a || !b) return false;
+  const keysA = Object.keys(a);
+  const keysB = Object.keys(b);
+  if (keysA.length !== keysB.length) return false;
+  for (const key of keysA) {
+    const va = a[key];
+    const vb = b[key];
+    if (va === vb) continue;
+    if (
+      typeof va === "object" &&
+      va !== null &&
+      typeof vb === "object" &&
+      vb !== null
+    ) {
+      const sa = (va as Record<string, unknown>).$state;
+      const sb = (vb as Record<string, unknown>).$state;
+      if (typeof sa === "string" && sa === sb) continue;
+    }
+    return false;
+  }
+  return true;
+}
+
+/**
+ * Structural equality check for ValidationConfig.
+ */
+function validationConfigEqual(
+  a: ValidationConfig,
+  b: ValidationConfig,
+): boolean {
+  if (a === b) return true;
+  if (a.validateOn !== b.validateOn) return false;
+  const ac = a.checks ?? [];
+  const bc = b.checks ?? [];
+  if (ac.length !== bc.length) return false;
+  for (let i = 0; i < ac.length; i++) {
+    const ca = ac[i]!;
+    const cb = bc[i]!;
+    if (ca.type !== cb.type) return false;
+    if (ca.message !== cb.message) return false;
+    if (!dynamicArgsEqual(ca.args, cb.args)) return false;
+  }
+  return true;
+}
+
+/**
+ * Provider for validation
+ */
+export const ValidationProvider = defineComponent({
+  name: "ValidationProvider",
+  props: {
+    customFunctions: {
+      type: Object as PropType<Record<string, ValidationFunction>>,
+      default: () => ({}),
+    },
+  },
+  setup(props, { slots }) {
+    const { state } = useStateStore();
+
+    const fieldStates = ref<Record<string, FieldValidationState>>({});
+    const fieldConfigs = ref<Record<string, ValidationConfig>>({});
+
+    const registerField = (path: string, config: ValidationConfig) => {
+      const existing = fieldConfigs.value[path];
+      if (existing && validationConfigEqual(existing, config)) return;
+      fieldConfigs.value = { ...fieldConfigs.value, [path]: config };
+    };
+
+    const validate = (
+      path: string,
+      config: ValidationConfig,
+    ): ValidationResult => {
+      const currentState = state.value;
+      const segments = path.split("/").filter(Boolean);
+      let value: unknown = currentState;
+      for (const seg of segments) {
+        if (value != null && typeof value === "object") {
+          value = (value as Record<string, unknown>)[seg];
+        } else {
+          value = undefined;
+          break;
+        }
+      }
+      const result = runValidation(config, {
+        value,
+        stateModel: currentState,
+        customFunctions: props.customFunctions,
+      });
+
+      fieldStates.value = {
+        ...fieldStates.value,
+        [path]: {
+          touched: fieldStates.value[path]?.touched ?? true,
+          validated: true,
+          result,
+        },
+      };
+
+      return result;
+    };
+
+    const touch = (path: string) => {
+      fieldStates.value = {
+        ...fieldStates.value,
+        [path]: {
+          ...fieldStates.value[path],
+          touched: true,
+          validated: fieldStates.value[path]?.validated ?? false,
+          result: fieldStates.value[path]?.result ?? null,
+        },
+      };
+    };
+
+    const clear = (path: string) => {
+      const { [path]: _, ...rest } = fieldStates.value;
+      fieldStates.value = rest;
+    };
+
+    const validateAll = (): boolean => {
+      let allValid = true;
+      for (const [path, config] of Object.entries(fieldConfigs.value)) {
+        const result = validate(path, config);
+        if (!result.valid) {
+          allValid = false;
+        }
+      }
+      return allValid;
+    };
+
+    provide<ValidationContextValue>(VALIDATION_KEY, {
+      get customFunctions() {
+        return props.customFunctions;
+      },
+      get fieldStates() {
+        return fieldStates.value;
+      },
+      validate,
+      touch,
+      clear,
+      validateAll,
+      registerField,
+    });
+
+    return () => slots.default?.();
+  },
+});
+
+/**
+ * Composable to access validation context (or null if not inside a ValidationProvider).
+ * Useful for components that optionally participate in form validation.
+ */
+export function useOptionalValidation(): ValidationContextValue | null {
+  return (
+    inject<ValidationContextValue>(
+      VALIDATION_KEY,
+      null as unknown as ValidationContextValue,
+    ) ?? null
+  );
+}
+
+/**
+ * Composable to access validation context
+ */
+export function useValidation(): ValidationContextValue {
+  const ctx = inject<ValidationContextValue>(VALIDATION_KEY);
+  if (!ctx) {
+    throw new Error("useValidation must be used within a ValidationProvider");
+  }
+  return ctx;
+}
+
+/**
+ * Composable to get validation state for a field
+ */
+export function useFieldValidation(
+  path: string,
+  config?: ValidationConfig,
+): {
+  state: ComputedRef<FieldValidationState>;
+  validate: () => ValidationResult;
+  touch: () => void;
+  clear: () => void;
+  errors: ComputedRef<string[]>;
+  isValid: ComputedRef<boolean>;
+} {
+  const ctx = useValidation();
+
+  onMounted(() => {
+    if (path && config) {
+      ctx.registerField(path, config);
+    }
+  });
+
+  onUnmounted(() => {
+    ctx.clear(path);
+  });
+
+  const defaultState: FieldValidationState = {
+    touched: false,
+    validated: false,
+    result: null,
+  };
+
+  return {
+    state: computed(() => ctx.fieldStates[path] ?? defaultState),
+    validate: () => ctx.validate(path, config ?? { checks: [] }),
+    touch: () => ctx.touch(path),
+    clear: () => ctx.clear(path),
+    errors: computed(() => ctx.fieldStates[path]?.result?.errors ?? []),
+    isValid: computed(() => ctx.fieldStates[path]?.result?.valid ?? true),
+  };
+}

packages/vue/src/composables/visibility.test.ts

@@ -0,0 +1,97 @@
+import { describe, it, expect, vi } from "vitest";
+import { defineComponent, h, type Component, type ComputedRef } from "vue";
+import { mount } from "@vue/test-utils";
+import { StateProvider, useStateStore } from "./state";
+import { VisibilityProvider, useVisibility, useIsVisible } from "./visibility";
+
+/** Mount StateProvider → VisibilityProvider with a child that captures context. */
+function withProviders<T>(
+  composable: () => T,
+  initialState: Record<string, unknown> = {},
+): { result: T } {
+  let result!: T;
+  const Child = defineComponent({
+    setup() {
+      result = composable();
+      return () => h("div");
+    },
+  });
+  mount(StateProvider as Component, {
+    props: { initialState } as any,
+    slots: {
+      default: () =>
+        h(VisibilityProvider as Component, null, {
+          default: () => h(Child),
+        }),
+    },
+  });
+  return { result };
+}
+
+describe("VisibilityProvider — provide/inject", () => {
+  it("useVisibility() throws outside a VisibilityProvider", () => {
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+    expect(() => useVisibility()).toThrow(
+      "useVisibility must be used within a VisibilityProvider",
+    );
+    warn.mockRestore();
+  });
+
+  it("useVisibility() returns a context with isVisible and ctx", () => {
+    const { result } = withProviders(() => useVisibility());
+    expect(typeof result.isVisible).toBe("function");
+    expect(result.ctx).toBeDefined();
+    expect(result.ctx.value).toBeDefined();
+  });
+});
+
+describe("useIsVisible — state integration", () => {
+  it("undefined condition returns true", () => {
+    const { result } = withProviders(() => useVisibility());
+    expect(result.isVisible(undefined)).toBe(true);
+  });
+
+  it("{ $state: '/flag' } returns true when state flag is truthy", () => {
+    const { result } = withProviders(() => useVisibility(), { flag: true });
+    expect(result.isVisible({ $state: "/flag" })).toBe(true);
+  });
+
+  it("{ $state: '/flag' } returns false when state flag is falsy", () => {
+    const { result } = withProviders(() => useVisibility(), { flag: false });
+    expect(result.isVisible({ $state: "/flag" })).toBe(false);
+  });
+
+  it("ctx is a ComputedRef whose .value reflects current state", () => {
+    const { result } = withProviders(() => useVisibility(), { count: 3 });
+    expect(result.ctx.value.stateModel).toEqual({ count: 3 });
+  });
+});
+
+describe("useIsVisible — reactivity", () => {
+  it("returns a ComputedRef<boolean> that updates when state changes", () => {
+    let storeCtx!: ReturnType<typeof useStateStore>;
+    let isVisible!: ComputedRef<boolean>;
+
+    const Child = defineComponent({
+      setup() {
+        storeCtx = useStateStore();
+        isVisible = useIsVisible({ $state: "/flag" });
+        return () => h("div");
+      },
+    });
+
+    mount(StateProvider as Component, {
+      props: { initialState: { flag: false } } as any,
+      slots: {
+        default: () =>
+          h(VisibilityProvider as Component, null, {
+            default: () => h(Child),
+          }),
+      },
+    });
+
+    expect(isVisible.value).toBe(false);
+    storeCtx.set("/flag", true);
+    expect(isVisible.value).toBe(true);
+  });
+});

packages/vue/src/composables/visibility.ts

@@ -0,0 +1,68 @@
+import {
+  computed,
+  defineComponent,
+  inject,
+  provide,
+  type ComputedRef,
+} from "vue";
+import {
+  evaluateVisibility,
+  type VisibilityCondition,
+  type VisibilityContext as CoreVisibilityContext,
+} from "@json-render/core";
+import { useStateStore } from "./state";
+
+/**
+ * Visibility context value
+ */
+export interface VisibilityContextValue {
+  /** Evaluate a visibility condition */
+  isVisible: (condition: VisibilityCondition | undefined) => boolean;
+  /** The underlying visibility context (reactive) */
+  ctx: ComputedRef<CoreVisibilityContext>;
+}
+
+const VISIBILITY_KEY = Symbol("json-render:visibility");
+
+/**
+ * Provider for visibility evaluation
+ */
+export const VisibilityProvider = defineComponent({
+  name: "VisibilityProvider",
+  setup(_, { slots }) {
+    const { state } = useStateStore();
+
+    const ctx = computed<CoreVisibilityContext>(() => ({
+      stateModel: state.value,
+    }));
+
+    const isVisible = (condition: VisibilityCondition | undefined): boolean =>
+      evaluateVisibility(condition, ctx.value);
+
+    provide<VisibilityContextValue>(VISIBILITY_KEY, { isVisible, ctx });
+
+    return () => slots.default?.();
+  },
+});
+
+/**
+ * Composable to access visibility evaluation
+ */
+export function useVisibility(): VisibilityContextValue {
+  const ctx = inject<VisibilityContextValue>(VISIBILITY_KEY);
+  if (!ctx) {
+    throw new Error("useVisibility must be used within a VisibilityProvider");
+  }
+  return ctx;
+}
+
+/**
+ * Composable to check if a condition is visible. Returns a reactive
+ * `ComputedRef<boolean>` so the result updates whenever state changes.
+ */
+export function useIsVisible(
+  condition: VisibilityCondition | undefined,
+): ComputedRef<boolean> {
+  const { ctx } = useVisibility();
+  return computed(() => evaluateVisibility(condition, ctx.value));
+}

packages/vue/src/dynamic-forms.test.ts

@@ -0,0 +1,482 @@
+import { describe, it, expect, vi } from "vitest";
+import { defineComponent, h, nextTick, type Component } from "vue";
+import { mount } from "@vue/test-utils";
+import type { Spec } from "@json-render/core";
+import { StateProvider, useStateStore } from "./composables/state";
+import { VisibilityProvider } from "./composables/visibility";
+import { ActionProvider } from "./composables/actions";
+import { ValidationProvider } from "./composables/validation";
+import { useFieldValidation } from "./composables/validation";
+import { useBoundProp } from "./hooks";
+import {
+  Renderer,
+  JSONUIProvider,
+  type ComponentRegistry,
+  type ComponentRenderProps,
+} from "./renderer";
+
+// =============================================================================
+// Stub components
+// =============================================================================
+
+const Button = defineComponent({
+  name: "Button",
+  props: {
+    element: { type: Object, required: true },
+    emit: { type: Function, required: true },
+    on: { type: Function, required: true },
+    bindings: { type: Object, default: undefined },
+    loading: { type: Boolean, default: undefined },
+  },
+  setup(props) {
+    return () =>
+      h(
+        "button",
+        { "data-testid": "btn", onClick: () => props.emit("press") },
+        String((props.element as any).props?.label ?? ""),
+      );
+  },
+});
+
+const Text = defineComponent({
+  name: "Text",
+  props: {
+    element: { type: Object, required: true },
+    emit: { type: Function, required: true },
+    on: { type: Function, required: true },
+    bindings: { type: Object, default: undefined },
+    loading: { type: Boolean, default: undefined },
+  },
+  setup(props) {
+    return () => {
+      const value = (props.element as any).props?.text;
+      return h(
+        "span",
+        { "data-testid": "text" },
+        value == null
+          ? ""
+          : typeof value === "string"
+            ? value
+            : JSON.stringify(value),
+      );
+    };
+  },
+});
+
+const Stack = defineComponent({
+  name: "Stack",
+  props: {
+    element: { type: Object, required: true },
+    emit: { type: Function, required: true },
+    on: { type: Function, required: true },
+    bindings: { type: Object, default: undefined },
+    loading: { type: Boolean, default: undefined },
+  },
+  setup(_props, { slots }) {
+    return () => h("div", { "data-testid": "stack" }, slots.default?.());
+  },
+});
+
+const InputField = defineComponent({
+  name: "InputField",
+  props: {
+    element: { type: Object, required: true },
+    emit: { type: Function, required: true },
+    on: { type: Function, required: true },
+    bindings: { type: Object, default: undefined },
+    loading: { type: Boolean, default: undefined },
+  },
+  setup(props) {
+    const elProps = (props.element as any).props ?? {};
+    const bindingPath = (props.bindings as Record<string, string>)?.value;
+    const [boundValue, setBoundValue] = useBoundProp<string>(
+      elProps.value as string | undefined,
+      bindingPath,
+    );
+
+    const hasValidation = !!(bindingPath && elProps.checks?.length);
+    const config = hasValidation ? { checks: elProps.checks ?? [] } : undefined;
+    const { errors } = useFieldValidation(bindingPath ?? "", config);
+
+    return () =>
+      h("div", null, [
+        elProps.label ? h("label", null, elProps.label) : null,
+        h("input", {
+          "data-testid": "input",
+          value: boundValue ?? "",
+          onInput: (e: Event) =>
+            setBoundValue((e.target as HTMLInputElement).value),
+        }),
+        errors.value.length > 0
+          ? h("span", { "data-testid": "input-error" }, errors.value[0])
+          : null,
+      ]);
+  },
+});
+
+const Select = defineComponent({
+  name: "Select",
+  props: {
+    element: { type: Object, required: true },
+    emit: { type: Function, required: true },
+    on: { type: Function, required: true },
+    bindings: { type: Object, default: undefined },
+    loading: { type: Boolean, default: undefined },
+  },
+  setup(props) {
+    const elProps = (props.element as any).props ?? {};
+    const bindingPath = (props.bindings as Record<string, string>)?.value;
+    const [boundValue] = useBoundProp<string>(
+      elProps.value as string | undefined,
+      bindingPath,
+    );
+    return () => h("span", { "data-testid": "select-value" }, boundValue ?? "");
+  },
+});
+
+const registry: ComponentRegistry = {
+  Button: Button as unknown as Component,
+  Text: Text as unknown as Component,
+  Input: InputField as unknown as Component,
+  Select: Select as unknown as Component,
+  Stack: Stack as unknown as Component,
+};
+
+// State probe to read state from tests
+const StateProbe = defineComponent({
+  name: "StateProbe",
+  setup() {
+    const { state } = useStateStore();
+    return () =>
+      h("pre", { "data-testid": "state-probe" }, JSON.stringify(state.value));
+  },
+});
+
+function getState(wrapper: ReturnType<typeof mount>): Record<string, unknown> {
+  return JSON.parse(wrapper.find("[data-testid='state-probe']").text());
+}
+
+// =============================================================================
+// Mount helper
+// =============================================================================
+
+function mountWithProviders(
+  spec: Spec,
+  opts: {
+    functions?: Record<string, (args: Record<string, unknown>) => unknown>;
+    handlers?: Record<
+      string,
+      (params: Record<string, unknown>) => Promise<void> | void
+    >;
+    initialState?: Record<string, unknown>;
+  } = {},
+) {
+  return mount(JSONUIProvider as Component, {
+    props: {
+      registry,
+      initialState: opts.initialState ?? spec.state ?? {},
+      functions: opts.functions,
+      handlers: opts.handlers,
+    } as any,
+    slots: {
+      default: () => [h(Renderer, { spec, registry }), h(StateProbe)],
+    },
+  });
+}
+
+// =============================================================================
+// $computed expressions in rendering
+// =============================================================================
+
+describe("$computed expressions in rendering", () => {
+  it("resolves a $computed prop using provided functions", () => {
+    const spec: Spec = {
+      state: { first: "Jane", last: "Doe" },
+      root: "main",
+      elements: {
+        main: {
+          type: "Text",
+          props: {
+            text: {
+              $computed: "fullName",
+              args: {
+                first: { $state: "/first" },
+                last: { $state: "/last" },
+              },
+            },
+          },
+          children: [],
+        },
+      },
+    };
+
+    const functions = {
+      fullName: (args: Record<string, unknown>) => `${args.first} ${args.last}`,
+    };
+
+    const wrapper = mountWithProviders(spec, { functions });
+    expect(wrapper.find("[data-testid='text']").text()).toBe("Jane Doe");
+  });
+
+  it("renders gracefully when functions prop is omitted", () => {
+    const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    const spec: Spec = {
+      state: {},
+      root: "main",
+      elements: {
+        main: {
+          type: "Text",
+          props: {
+            text: { $computed: "missing" },
+          },
+          children: [],
+        },
+      },
+    };
+
+    const wrapper = mountWithProviders(spec);
+    expect(wrapper.find("[data-testid='text']").text()).toBe("");
+    warnSpy.mockRestore();
+  });
+});
+
+// =============================================================================
+// Watchers
+// =============================================================================
+
+describe("watchers (watch field)", () => {
+  it("does not fire on initial render, fires when watched state changes", async () => {
+    const loadCities = vi.fn();
+
+    const spec: Spec = {
+      state: { form: { country: "" }, citiesLoaded: false },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["btn", "watcher"],
+        },
+        btn: {
+          type: "Button",
+          props: { label: "Set Country" },
+          on: {
+            press: [
+              {
+                action: "setState",
+                params: { statePath: "/form/country", value: "US" },
+              },
+            ],
+          },
+          children: [],
+        },
+        watcher: {
+          type: "Select",
+          props: { value: { $state: "/form/country" } },
+          watch: {
+            "/form/country": {
+              action: "loadCities",
+              params: { country: { $state: "/form/country" } },
+            },
+          },
+          children: [],
+        },
+      },
+    };
+
+    const wrapper = mountWithProviders(spec, { handlers: { loadCities } });
+
+    expect(loadCities).not.toHaveBeenCalled();
+
+    await wrapper.find("[data-testid='btn']").trigger("click");
+    await nextTick();
+    await nextTick();
+
+    expect(loadCities).toHaveBeenCalledTimes(1);
+    expect(loadCities).toHaveBeenCalledWith(
+      expect.objectContaining({ country: "US" }),
+    );
+  });
+
+  it("fires multiple action bindings on the same watch path", async () => {
+    const action1 = vi.fn();
+    const action2 = vi.fn();
+
+    const spec: Spec = {
+      state: { value: "a" },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["btn", "watcher"],
+        },
+        btn: {
+          type: "Button",
+          props: { label: "Change" },
+          on: {
+            press: [
+              {
+                action: "setState",
+                params: { statePath: "/value", value: "b" },
+              },
+            ],
+          },
+          children: [],
+        },
+        watcher: {
+          type: "Text",
+          props: { text: { $state: "/value" } },
+          watch: {
+            "/value": [{ action: "action1" }, { action: "action2" }],
+          },
+          children: [],
+        },
+      },
+    };
+
+    const wrapper = mountWithProviders(spec, {
+      handlers: { action1, action2 },
+    });
+
+    await wrapper.find("[data-testid='btn']").trigger("click");
+    await nextTick();
+    await nextTick();
+
+    expect(action1).toHaveBeenCalledTimes(1);
+    expect(action2).toHaveBeenCalledTimes(1);
+  });
+});
+
+// =============================================================================
+// validateForm action
+// =============================================================================
+
+describe("validateForm action", () => {
+  it("writes { valid: false, errors } when a required field is empty", async () => {
+    const spec: Spec = {
+      state: { form: { email: "" }, result: null },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["emailInput", "submitBtn"],
+        },
+        emailInput: {
+          type: "Input",
+          props: {
+            label: "Email",
+            value: { $bindState: "/form/email" },
+            checks: [{ type: "required", message: "Email is required" }],
+          },
+          children: [],
+        },
+        submitBtn: {
+          type: "Button",
+          props: { label: "Submit" },
+          on: {
+            press: [
+              {
+                action: "validateForm",
+                params: { statePath: "/result" },
+              },
+            ],
+          },
+          children: [],
+        },
+      },
+    };
+
+    const wrapper = mountWithProviders(spec);
+    await wrapper.find("[data-testid='btn']").trigger("click");
+    await nextTick();
+
+    const state = getState(wrapper);
+    expect(state.result).toEqual({
+      valid: false,
+      errors: { "/form/email": ["Email is required"] },
+    });
+  });
+
+  it("writes { valid: true, errors: {} } when all fields pass validation", async () => {
+    const spec: Spec = {
+      state: { form: { email: "test@example.com" }, result: null },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["emailInput", "submitBtn"],
+        },
+        emailInput: {
+          type: "Input",
+          props: {
+            label: "Email",
+            value: { $bindState: "/form/email" },
+            checks: [{ type: "required", message: "Email is required" }],
+          },
+          children: [],
+        },
+        submitBtn: {
+          type: "Button",
+          props: { label: "Submit" },
+          on: {
+            press: [
+              {
+                action: "validateForm",
+                params: { statePath: "/result" },
+              },
+            ],
+          },
+          children: [],
+        },
+      },
+    };
+
+    const wrapper = mountWithProviders(spec);
+    await wrapper.find("[data-testid='btn']").trigger("click");
+    await nextTick();
+
+    const state = getState(wrapper);
+    expect(state.result).toEqual({ valid: true, errors: {} });
+  });
+
+  it("defaults to /formValidation when no statePath is provided", async () => {
+    const spec: Spec = {
+      state: { form: { name: "filled" } },
+      root: "wrapper",
+      elements: {
+        wrapper: {
+          type: "Stack",
+          props: {},
+          children: ["nameInput", "submitBtn"],
+        },
+        nameInput: {
+          type: "Input",
+          props: {
+            label: "Name",
+            value: { $bindState: "/form/name" },
+            checks: [{ type: "required", message: "Required" }],
+          },
+          children: [],
+        },
+        submitBtn: {
+          type: "Button",
+          props: { label: "Submit" },
+          on: {
+            press: [{ action: "validateForm" }],
+          },
+          children: [],
+        },
+      },
+    };
+
+    const wrapper = mountWithProviders(spec);
+    await wrapper.find("[data-testid='btn']").trigger("click");
+    await nextTick();
+
+    const state = getState(wrapper);
+    expect(state.formValidation).toEqual({ valid: true, errors: {} });
+  });
+});

packages/vue/src/hooks.test.ts

@@ -0,0 +1,347 @@
+import { describe, it, expect, vi, afterEach } from "vitest";
+import { defineComponent, h, ref, type Component } from "vue";
+import { mount } from "@vue/test-utils";
+import { SPEC_DATA_PART_TYPE } from "@json-render/core";
+import { StateProvider, useStateStore } from "./composables/state";
+import {
+  flatToTree,
+  buildSpecFromParts,
+  getTextFromParts,
+  useBoundProp,
+  useUIStream,
+  useJsonRenderMessage,
+  type DataPart,
+} from "./hooks";
+
+// ---------------------------------------------------------------------------
+// Test helpers
+// ---------------------------------------------------------------------------
+
+/** Mount inside a StateProvider and capture a composable's result. */
+function withStateProvider<T>(
+  composable: () => T,
+  initialState: Record<string, unknown> = {},
+): { result: T } {
+  let result!: T;
+  const Child = defineComponent({
+    setup() {
+      result = composable();
+      return () => h("div");
+    },
+  });
+  mount(StateProvider as Component, {
+    props: { initialState } as any,
+    slots: { default: () => h(Child) },
+  });
+  return { result };
+}
+
+/** Create a simple ReadableStream from a string (for fetch mocks). */
+function makeReadableStream(text: string): ReadableStream<Uint8Array> {
+  const encoder = new TextEncoder();
+  return new ReadableStream({
+    start(controller) {
+      controller.enqueue(encoder.encode(text));
+      controller.close();
+    },
+  });
+}
+
+// ---------------------------------------------------------------------------
+// flatToTree
+// ---------------------------------------------------------------------------
+
+describe("flatToTree", () => {
+  it("converts flat elements into a Spec with root and children", () => {
+    const elements = [
+      { key: "root", type: "Stack", props: {}, parentKey: undefined },
+      {
+        key: "child1",
+        type: "Text",
+        props: { content: "hello" },
+        parentKey: "root",
+      },
+    ];
+    const spec = flatToTree(elements as any);
+    expect(spec.root).toBe("root");
+    expect(spec.elements["root"]?.children).toContain("child1");
+    expect(spec.elements["child1"]).toBeDefined();
+  });
+
+  it("handles a single root element with no children", () => {
+    const elements = [
+      { key: "root", type: "Text", props: {}, parentKey: undefined },
+    ];
+    const spec = flatToTree(elements as any);
+    expect(spec.root).toBe("root");
+    expect(spec.elements["root"]?.children).toEqual([]);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildSpecFromParts
+// ---------------------------------------------------------------------------
+
+describe("buildSpecFromParts", () => {
+  it("returns null when no spec parts present", () => {
+    const parts: DataPart[] = [{ type: "text", text: "hello" }];
+    expect(buildSpecFromParts(parts)).toBeNull();
+  });
+
+  it("returns null for empty array", () => {
+    expect(buildSpecFromParts([])).toBeNull();
+  });
+
+  it("returns a Spec when a snapshot spec data part is present", () => {
+    const part: DataPart = {
+      type: SPEC_DATA_PART_TYPE,
+      data: {
+        type: "flat",
+        spec: {
+          root: "r",
+          elements: { r: { type: "Text", props: { content: "hi" } } },
+        },
+      },
+    };
+    const result = buildSpecFromParts([part]);
+    expect(result?.root).toBe("r");
+    expect(result?.elements["r"]).toBeDefined();
+  });
+
+  it("applies patch operations incrementally", () => {
+    const parts: DataPart[] = [
+      {
+        type: SPEC_DATA_PART_TYPE,
+        data: {
+          type: "patch",
+          patch: { op: "add", path: "/root", value: "myRoot" },
+        },
+      },
+    ];
+    const result = buildSpecFromParts(parts);
+    expect(result?.root).toBe("myRoot");
+  });
+
+  it("skips malformed data parts silently", () => {
+    const parts: DataPart[] = [
+      { type: SPEC_DATA_PART_TYPE, data: { type: "unknown" } },
+    ];
+    expect(buildSpecFromParts(parts)).toBeNull();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// getTextFromParts
+// ---------------------------------------------------------------------------
+
+describe("getTextFromParts", () => {
+  it("concatenates text parts with double newlines", () => {
+    const parts: DataPart[] = [
+      { type: "text", text: "hello" },
+      { type: "text", text: "world" },
+    ];
+    expect(getTextFromParts(parts)).toBe("hello\n\nworld");
+  });
+
+  it("ignores non-text parts", () => {
+    const parts: DataPart[] = [
+      { type: "other", data: {} },
+      { type: "text", text: "hi" },
+    ];
+    expect(getTextFromParts(parts)).toBe("hi");
+  });
+
+  it("returns empty string for empty array", () => {
+    expect(getTextFromParts([])).toBe("");
+  });
+
+  it("filters out empty/whitespace text parts", () => {
+    const parts: DataPart[] = [
+      { type: "text", text: "  " },
+      { type: "text", text: "real" },
+    ];
+    expect(getTextFromParts(parts)).toBe("real");
+  });
+});
+
+// ---------------------------------------------------------------------------
+// useBoundProp
+// ---------------------------------------------------------------------------
+
+describe("useBoundProp", () => {
+  it("returns the prop value and a no-op setter when no binding path", () => {
+    const { result } = withStateProvider(() =>
+      useBoundProp("hello", undefined),
+    );
+    const [value, setValue] = result;
+    expect(value).toBe("hello");
+    expect(() => setValue("new")).not.toThrow();
+  });
+
+  it("returns undefined prop value when propValue is undefined", () => {
+    const { result } = withStateProvider(() =>
+      useBoundProp<string>(undefined, undefined),
+    );
+    expect(result[0]).toBeUndefined();
+  });
+
+  it("setter writes to state at the binding path", () => {
+    let storeCtx!: ReturnType<typeof useStateStore>;
+    let setter!: (v: string) => void;
+
+    const Child = defineComponent({
+      setup() {
+        storeCtx = useStateStore();
+        const [, s] = useBoundProp<string>("Alice", "/name");
+        setter = s;
+        return () => h("div");
+      },
+    });
+
+    mount(StateProvider as Component, {
+      props: { initialState: { name: "Alice" } } as any,
+      slots: { default: () => h(Child) },
+    });
+
+    setter("Bob");
+    expect(storeCtx.get("/name")).toBe("Bob");
+  });
+});
+
+// ---------------------------------------------------------------------------
+// useUIStream
+// ---------------------------------------------------------------------------
+
+describe("useUIStream", () => {
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it("send() sets isStreaming true then false after completion", async () => {
+    const patchLine =
+      JSON.stringify({ op: "add", path: "/root", value: "myRoot" }) +
+      "\n" +
+      JSON.stringify({
+        op: "add",
+        path: "/elements/myRoot",
+        value: { type: "Text", props: {} },
+      }) +
+      "\n";
+
+    vi.stubGlobal(
+      "fetch",
+      vi.fn().mockResolvedValue({
+        ok: true,
+        body: makeReadableStream(patchLine),
+      }),
+    );
+
+    let streamResult!: ReturnType<typeof useUIStream>;
+    const Child = defineComponent({
+      setup() {
+        streamResult = useUIStream({ api: "/api/ui" });
+        return () => h("div");
+      },
+    });
+    mount(StateProvider as Component, {
+      props: { initialState: {} } as any,
+      slots: { default: () => h(Child) },
+    });
+
+    expect(streamResult.isStreaming.value).toBe(false);
+    const promise = streamResult.send("build me a UI");
+    expect(streamResult.isStreaming.value).toBe(true);
+    await promise;
+    expect(streamResult.isStreaming.value).toBe(false);
+    expect(streamResult.spec.value?.root).toBe("myRoot");
+  });
+
+  it("error is set when fetch fails", async () => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn().mockRejectedValue(new Error("Network error")),
+    );
+
+    let streamResult!: ReturnType<typeof useUIStream>;
+    const Child = defineComponent({
+      setup() {
+        streamResult = useUIStream({ api: "/api/ui" });
+        return () => h("div");
+      },
+    });
+    mount(StateProvider as Component, {
+      props: { initialState: {} } as any,
+      slots: { default: () => h(Child) },
+    });
+
+    await streamResult.send("fail");
+    expect(streamResult.error.value?.message).toBe("Network error");
+  });
+
+  it("clear() resets spec and error", async () => {
+    vi.stubGlobal("fetch", vi.fn().mockRejectedValue(new Error("oops")));
+
+    let streamResult!: ReturnType<typeof useUIStream>;
+    const Child = defineComponent({
+      setup() {
+        streamResult = useUIStream({ api: "/api/ui" });
+        return () => h("div");
+      },
+    });
+    mount(StateProvider as Component, {
+      props: { initialState: {} } as any,
+      slots: { default: () => h(Child) },
+    });
+
+    await streamResult.send("fail");
+    expect(streamResult.error.value).not.toBeNull();
+    streamResult.clear();
+    expect(streamResult.error.value).toBeNull();
+    expect(streamResult.spec.value).toBeNull();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// useJsonRenderMessage
+// ---------------------------------------------------------------------------
+
+describe("useJsonRenderMessage", () => {
+  it("returns null spec and false hasSpec when no spec parts", () => {
+    const { spec, hasSpec } = useJsonRenderMessage([
+      { type: "text", text: "hi" },
+    ]);
+    expect(spec.value).toBeNull();
+    expect(hasSpec.value).toBe(false);
+  });
+
+  it("extracts text from text parts", () => {
+    const { text } = useJsonRenderMessage([
+      { type: "text", text: "hello" },
+      { type: "text", text: "world" },
+    ]);
+    expect(text.value).toBe("hello\n\nworld");
+  });
+
+  it("is reactive when passed a Ref<DataPart[]>", () => {
+    const parts = ref<DataPart[]>([]);
+    const { text, spec, hasSpec } = useJsonRenderMessage(parts);
+    expect(text.value).toBe("");
+    expect(spec.value).toBeNull();
+
+    parts.value = [{ type: "text", text: "hello" }];
+    expect(text.value).toBe("hello");
+
+    parts.value = [
+      ...parts.value,
+      {
+        type: SPEC_DATA_PART_TYPE,
+        data: {
+          type: "flat",
+          spec: { root: "r", elements: { r: { type: "Text", props: {} } } },
+        },
+      },
+    ];
+    expect(spec.value?.root).toBe("r");
+    expect(hasSpec.value).toBe(true);
+  });
+});

packages/vue/src/hooks.ts

@@ -0,0 +1,830 @@
+import {
+  ref,
+  shallowRef,
+  computed,
+  onUnmounted,
+  isRef,
+  type Ref,
+  type ComputedRef,
+} from "vue";
+import { useStateStore } from "./composables/state";
+import type {
+  Spec,
+  UIElement,
+  FlatElement,
+  JsonPatch,
+  SpecDataPart,
+} from "@json-render/core";
+import {
+  setByPath,
+  getByPath,
+  addByPath,
+  removeByPath,
+  createMixedStreamParser,
+  applySpecPatch,
+  nestedToFlat,
+  SPEC_DATA_PART_TYPE,
+} from "@json-render/core";
+
+/**
+ * Token usage metadata from AI generation
+ */
+export interface TokenUsage {
+  promptTokens: number;
+  completionTokens: number;
+  totalTokens: number;
+}
+
+/**
+ * Parse result for a single line -- either a patch or usage metadata
+ */
+type ParsedLine =
+  | { type: "patch"; patch: JsonPatch }
+  | { type: "usage"; usage: TokenUsage }
+  | null;
+
+/**
+ * Parse a single JSON line (patch or metadata)
+ */
+function parseLine(line: string): ParsedLine {
+  try {
+    const trimmed = line.trim();
+    if (!trimmed || trimmed.startsWith("//")) {
+      return null;
+    }
+    const parsed = JSON.parse(trimmed);
+
+    // Check for usage metadata
+    if (parsed.__meta === "usage") {
+      return {
+        type: "usage",
+        usage: {
+          promptTokens: parsed.promptTokens ?? 0,
+          completionTokens: parsed.completionTokens ?? 0,
+          totalTokens: parsed.totalTokens ?? 0,
+        },
+      };
+    }
+
+    return { type: "patch", patch: parsed as JsonPatch };
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Set a value at a spec path (for add/replace operations).
+ */
+function setSpecValue(newSpec: Spec, path: string, value: unknown): void {
+  if (path === "/root") {
+    newSpec.root = value as string;
+    return;
+  }
+
+  if (path === "/state") {
+    newSpec.state = value as Record<string, unknown>;
+    return;
+  }
+
+  if (path.startsWith("/state/")) {
+    if (!newSpec.state) newSpec.state = {};
+    const statePath = path.slice("/state".length); // e.g. "/posts"
+    setByPath(newSpec.state as Record<string, unknown>, statePath, value);
+    return;
+  }
+
+  if (path.startsWith("/elements/")) {
+    const pathParts = path.slice("/elements/".length).split("/");
+    const elementKey = pathParts[0];
+    if (!elementKey) return;
+
+    if (pathParts.length === 1) {
+      newSpec.elements[elementKey] = value as UIElement;
+    } else {
+      const element = newSpec.elements[elementKey];
+      if (element) {
+        const propPath = "/" + pathParts.slice(1).join("/");
+        const newElement = { ...element };
+        setByPath(
+          newElement as unknown as Record<string, unknown>,
+          propPath,
+          value,
+        );
+        newSpec.elements[elementKey] = newElement;
+      }
+    }
+  }
+}
+
+/**
+ * Remove a value at a spec path.
+ */
+function removeSpecValue(newSpec: Spec, path: string): void {
+  if (path === "/state") {
+    delete newSpec.state;
+    return;
+  }
+
+  if (path.startsWith("/state/") && newSpec.state) {
+    const statePath = path.slice("/state".length);
+    removeByPath(newSpec.state as Record<string, unknown>, statePath);
+    return;
+  }
+
+  if (path.startsWith("/elements/")) {
+    const pathParts = path.slice("/elements/".length).split("/");
+    const elementKey = pathParts[0];
+    if (!elementKey) return;
+
+    if (pathParts.length === 1) {
+      const { [elementKey]: _, ...rest } = newSpec.elements;
+      newSpec.elements = rest;
+    } else {
+      const element = newSpec.elements[elementKey];
+      if (element) {
+        const propPath = "/" + pathParts.slice(1).join("/");
+        const newElement = { ...element };
+        removeByPath(
+          newElement as unknown as Record<string, unknown>,
+          propPath,
+        );
+        newSpec.elements[elementKey] = newElement;
+      }
+    }
+  }
+}
+
+/**
+ * Get a value at a spec path.
+ */
+function getSpecValue(spec: Spec, path: string): unknown {
+  if (path === "/root") return spec.root;
+  if (path === "/state") return spec.state;
+  if (path.startsWith("/state/") && spec.state) {
+    const statePath = path.slice("/state".length);
+    return getByPath(spec.state as Record<string, unknown>, statePath);
+  }
+  return getByPath(spec as unknown as Record<string, unknown>, path);
+}
+
+/**
+ * Apply an RFC 6902 JSON patch to the current spec.
+ * Supports add, remove, replace, move, copy, and test operations.
+ */
+function applyPatch(spec: Spec, patch: JsonPatch): Spec {
+  const newSpec = {
+    ...spec,
+    elements: { ...spec.elements },
+    ...(spec.state ? { state: { ...spec.state } } : {}),
+  };
+
+  switch (patch.op) {
+    case "add":
+    case "replace": {
+      setSpecValue(newSpec, patch.path, patch.value);
+      break;
+    }
+    case "remove": {
+      removeSpecValue(newSpec, patch.path);
+      break;
+    }
+    case "move": {
+      if (!patch.from) break;
+      const moveValue = getSpecValue(newSpec, patch.from);
+      removeSpecValue(newSpec, patch.from);
+      setSpecValue(newSpec, patch.path, moveValue);
+      break;
+    }
+    case "copy": {
+      if (!patch.from) break;
+      const copyValue = getSpecValue(newSpec, patch.from);
+      setSpecValue(newSpec, patch.path, copyValue);
+      break;
+    }
+    case "test": {
+      // test is a no-op for rendering purposes (validation only)
+      break;
+    }
+  }
+
+  return newSpec;
+}
+
+/**
+ * Options for useUIStream
+ */
+export interface UseUIStreamOptions {
+  /** API endpoint */
+  api: string;
+  /** Callback when complete */
+  onComplete?: (spec: Spec) => void;
+  /** Callback on error */
+  onError?: (error: Error) => void;
+}
+
+/**
+ * Return type for useUIStream
+ */
+export interface UseUIStreamReturn {
+  /** Current UI spec */
+  spec: Ref<Spec | null>;
+  /** Whether currently streaming */
+  isStreaming: Ref<boolean>;
+  /** Error if any */
+  error: Ref<Error | null>;
+  /** Token usage from the last generation */
+  usage: Ref<TokenUsage | null>;
+  /** Raw JSONL lines received from the stream (JSON patch lines) */
+  rawLines: Ref<string[]>;
+  /** Send a prompt to generate UI */
+  send: (prompt: string, context?: Record<string, unknown>) => Promise<void>;
+  /** Clear the current spec */
+  clear: () => void;
+}
+
+/**
+ * Composable for streaming UI generation
+ */
+export function useUIStream({
+  api,
+  onComplete,
+  onError,
+}: UseUIStreamOptions): UseUIStreamReturn {
+  const spec = shallowRef<Spec | null>(null);
+  const isStreaming = ref(false);
+  const error = ref<Error | null>(null);
+  const usage = ref<TokenUsage | null>(null);
+  const rawLines = ref<string[]>([]);
+
+  const onCompleteRef = ref(onComplete);
+  const onErrorRef = ref(onError);
+
+  let abortController: AbortController | null = null;
+
+  const clear = () => {
+    spec.value = null;
+    error.value = null;
+    usage.value = null;
+    rawLines.value = [];
+  };
+
+  const send = async (
+    prompt: string,
+    context?: Record<string, unknown>,
+  ): Promise<void> => {
+    // Abort any existing request
+    abortController?.abort();
+    abortController = new AbortController();
+
+    isStreaming.value = true;
+    error.value = null;
+    usage.value = null;
+    rawLines.value = [];
+
+    // Start with previous spec if provided, otherwise empty spec
+    const previousSpec = context?.previousSpec as Spec | undefined;
+    let currentSpec: Spec =
+      previousSpec && previousSpec.root
+        ? { ...previousSpec, elements: { ...previousSpec.elements } }
+        : { root: "", elements: {} };
+    spec.value = currentSpec;
+
+    try {
+      const response = await fetch(api, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+          prompt,
+          context,
+          currentSpec,
+        }),
+        signal: abortController.signal,
+      });
+
+      if (!response.ok) {
+        // Try to parse JSON error response for better error messages
+        let errorMessage = `HTTP error: ${response.status}`;
+        try {
+          const errorData = await response.json();
+          if (errorData.message) {
+            errorMessage = errorData.message;
+          } else if (errorData.error) {
+            errorMessage = errorData.error;
+          }
+        } catch {
+          // Ignore JSON parsing errors, use default message
+        }
+        throw new Error(errorMessage);
+      }
+
+      const reader = response.body?.getReader();
+      if (!reader) {
+        throw new Error("No response body");
+      }
+
+      const decoder = new TextDecoder();
+      let buffer = "";
+
+      while (true) {
+        const { done, value } = await reader.read();
+        if (done) break;
+
+        buffer += decoder.decode(value, { stream: true });
+
+        // Process complete lines
+        const lines = buffer.split("\n");
+        buffer = lines.pop() ?? "";
+
+        for (const line of lines) {
+          const trimmed = line.trim();
+          if (!trimmed) continue;
+          const result = parseLine(trimmed);
+          if (!result) continue;
+          if (result.type === "usage") {
+            usage.value = result.usage;
+          } else {
+            rawLines.value = [...rawLines.value, trimmed];
+            currentSpec = applyPatch(currentSpec, result.patch);
+            spec.value = { ...currentSpec };
+          }
+        }
+      }
+
+      // Process any remaining buffer
+      if (buffer.trim()) {
+        const trimmed = buffer.trim();
+        const result = parseLine(trimmed);
+        if (result) {
+          if (result.type === "usage") {
+            usage.value = result.usage;
+          } else {
+            rawLines.value = [...rawLines.value, trimmed];
+            currentSpec = applyPatch(currentSpec, result.patch);
+            spec.value = { ...currentSpec };
+          }
+        }
+      }
+
+      onCompleteRef.value?.(currentSpec);
+    } catch (err) {
+      if ((err as Error).name === "AbortError") {
+        return;
+      }
+      const resolvedError = err instanceof Error ? err : new Error(String(err));
+      error.value = resolvedError;
+      onErrorRef.value?.(resolvedError);
+    } finally {
+      isStreaming.value = false;
+    }
+  };
+
+  // Cleanup on unmount
+  onUnmounted(() => {
+    abortController?.abort();
+  });
+
+  return {
+    spec,
+    isStreaming,
+    error,
+    usage,
+    rawLines,
+    send,
+    clear,
+  };
+}
+
+/**
+ * Convert a flat element list to a Spec.
+ * Input elements use key/parentKey to establish identity and relationships.
+ * Output spec uses the map-based format where key is the map entry key
+ * and parent-child relationships are expressed through children arrays.
+ */
+export function flatToTree(elements: FlatElement[]): Spec {
+  const elementMap: Record<string, UIElement> = {};
+  let root = "";
+
+  // First pass: add all elements to map
+  for (const element of elements) {
+    elementMap[element.key] = {
+      type: element.type,
+      props: element.props,
+      children: [],
+      visible: element.visible,
+    };
+  }
+
+  // Second pass: build parent-child relationships
+  for (const element of elements) {
+    if (element.parentKey) {
+      const parent = elementMap[element.parentKey];
+      if (parent) {
+        if (!parent.children) {
+          parent.children = [];
+        }
+        parent.children.push(element.key);
+      }
+    } else {
+      root = element.key;
+    }
+  }
+
+  return { root, elements: elementMap };
+}
+
+// =============================================================================
+// useBoundProp — Two-way binding helper for $bindState/$bindItem expressions
+// =============================================================================
+
+/**
+ * Composable for two-way bound props. Returns `[value, setValue]` where:
+ *
+ * - `value` is the already-resolved prop value (passed through from render props)
+ * - `setValue` writes back to the bound state path (no-op if not bound)
+ *
+ * Designed to work with the `bindings` map that the renderer provides when
+ * a prop uses `{ $bindState: "/path" }` or `{ $bindItem: "field" }`.
+ *
+ * @example
+ * ```ts
+ * import { useBoundProp } from "@json-render/vue";
+ *
+ * const Input: ComponentFn<AppCatalog, "Input"> = ({ props, bindings }) => {
+ *   const [value, setValue] = useBoundProp<string>(props.value as string, bindings?.value);
+ *   return h("input", { value: value ?? "", onInput: (e) => setValue(e.target.value) });
+ * };
+ * ```
+ */
+export function useBoundProp<T>(
+  propValue: T | undefined,
+  bindingPath: string | undefined,
+): [T | undefined, (value: T) => void] {
+  const { set } = useStateStore();
+  return [
+    propValue,
+    (value: T) => {
+      if (bindingPath) set(bindingPath, value);
+    },
+  ];
+}
+
+// =============================================================================
+// buildSpecFromParts — Derive Spec from AI SDK data parts
+// =============================================================================
+
+/**
+ * A single part from the AI SDK's `message.parts` array. This is a minimal
+ * structural type so that library helpers do not depend on the AI SDK.
+ * Fields are optional because different part types carry different data:
+ * - Text parts have `text`
+ * - Data parts have `data`
+ */
+export interface DataPart {
+  type: string;
+  text?: string;
+  data?: unknown;
+}
+
+/**
+ * Type guard that validates a data part payload looks like a valid
+ * SpecDataPart before we cast it.
+ */
+function isSpecDataPart(data: unknown): data is SpecDataPart {
+  if (typeof data !== "object" || data === null) return false;
+  const obj = data as Record<string, unknown>;
+  switch (obj.type) {
+    case "patch":
+      return typeof obj.patch === "object" && obj.patch !== null;
+    case "flat":
+    case "nested":
+      return typeof obj.spec === "object" && obj.spec !== null;
+    default:
+      return false;
+  }
+}
+
+/**
+ * Build a `Spec` by replaying all spec data parts from a message's
+ * parts array. Returns `null` if no spec data parts are present.
+ *
+ * Works with the AI SDK's `UIMessage.parts` array. Picks out parts whose
+ * `type` is `SPEC_DATA_PART_TYPE` and processes them based on the payload's
+ * `type` discriminator: `"patch"`, `"flat"`, or `"nested"`.
+ */
+export function buildSpecFromParts(parts: DataPart[]): Spec | null {
+  const spec: Spec = { root: "", elements: {} };
+  let hasSpec = false;
+
+  for (const part of parts) {
+    if (part.type === SPEC_DATA_PART_TYPE) {
+      if (!isSpecDataPart(part.data)) continue;
+      const payload = part.data;
+      if (payload.type === "patch") {
+        hasSpec = true;
+        applySpecPatch(spec, payload.patch);
+      } else if (payload.type === "flat") {
+        hasSpec = true;
+        Object.assign(spec, payload.spec);
+      } else if (payload.type === "nested") {
+        hasSpec = true;
+        const flat = nestedToFlat(payload.spec);
+        Object.assign(spec, flat);
+      }
+    }
+  }
+
+  return hasSpec ? spec : null;
+}
+
+/**
+ * Extract and join all text content from a message's parts array.
+ *
+ * Filters for parts with `type === "text"`, trims each one, and joins them
+ * with double newlines so that text from separate agent steps renders as
+ * distinct paragraphs in markdown.
+ */
+export function getTextFromParts(parts: DataPart[]): string {
+  return parts
+    .filter(
+      (p): p is DataPart & { text: string } =>
+        p.type === "text" && typeof p.text === "string",
+    )
+    .map((p) => p.text.trim())
+    .filter(Boolean)
+    .join("\n\n");
+}
+
+// =============================================================================
+// useJsonRenderMessage — extract spec + text from message parts
+// =============================================================================
+
+/**
+ * Composable that extracts both the json-render spec and text content from a
+ * message's parts array. Accepts a plain `DataPart[]` or a `Ref<DataPart[]>`
+ * for reactive use in streaming scenarios.
+ *
+ * Returns `ComputedRef`s that recompute whenever `parts` changes.
+ *
+ * @example
+ * ```ts
+ * import { useJsonRenderMessage } from "@json-render/vue";
+ *
+ * const { spec, text, hasSpec } = useJsonRenderMessage(message.parts);
+ * ```
+ */
+export function useJsonRenderMessage(parts: DataPart[] | Ref<DataPart[]>): {
+  spec: ComputedRef<Spec | null>;
+  text: ComputedRef<string>;
+  hasSpec: ComputedRef<boolean>;
+} {
+  const partsRef = isRef(parts) ? parts : ref(parts);
+  const spec = computed(() => buildSpecFromParts(partsRef.value));
+  const text = computed(() => getTextFromParts(partsRef.value));
+  const hasSpec = computed(
+    () =>
+      spec.value !== null && Object.keys(spec.value.elements || {}).length > 0,
+  );
+  return { spec, text, hasSpec };
+}
+
+// =============================================================================
+// useChatUI — Chat + GenUI composable
+// =============================================================================
+
+/**
+ * A single message in the chat, which may contain text, a rendered UI spec, or both.
+ */
+export interface ChatMessage {
+  /** Unique message ID */
+  id: string;
+  /** Who sent this message */
+  role: "user" | "assistant";
+  /** Text content (conversational prose) */
+  text: string;
+  /** json-render Spec built from JSONL patches (null if no UI was generated) */
+  spec: Spec | null;
+}
+
+/**
+ * Options for useChatUI
+ */
+export interface UseChatUIOptions {
+  /** API endpoint that accepts `{ messages: Array<{ role, content }> }` and returns a text stream */
+  api: string;
+  /** Callback when streaming completes for a message */
+  onComplete?: (message: ChatMessage) => void;
+  /** Callback on error */
+  onError?: (error: Error) => void;
+}
+
+/**
+ * Return type for useChatUI
+ */
+export interface UseChatUIReturn {
+  /** All messages in the conversation */
+  messages: Ref<ChatMessage[]>;
+  /** Whether currently streaming an assistant response */
+  isStreaming: Ref<boolean>;
+  /** Error from the last request, if any */
+  error: Ref<Error | null>;
+  /** Send a user message */
+  send: (text: string) => Promise<void>;
+  /** Clear all messages and reset the conversation */
+  clear: () => void;
+}
+
+let chatMessageIdCounter = 0;
+function generateChatId(): string {
+  if (
+    typeof crypto !== "undefined" &&
+    typeof crypto.randomUUID === "function"
+  ) {
+    return crypto.randomUUID();
+  }
+  chatMessageIdCounter += 1;
+  return `msg-${Date.now()}-${chatMessageIdCounter}`;
+}
+
+/**
+ * Composable for chat + GenUI experiences.
+ *
+ * Manages a multi-turn conversation where each assistant message can contain
+ * both conversational text and a json-render UI spec. Sends the full message
+ * history to the API endpoint, reads the streamed response, and separates
+ * text lines from JSONL patch lines using `createMixedStreamParser`.
+ *
+ * @example
+ * ```ts
+ * const { messages, isStreaming, send, clear } = useChatUI({ api: "/api/chat" });
+ *
+ * await send("Compare weather in NYC and Tokyo");
+ * ```
+ */
+export function useChatUI({
+  api,
+  onComplete,
+  onError,
+}: UseChatUIOptions): UseChatUIReturn {
+  const messages = ref<ChatMessage[]>([]);
+  const isStreaming = ref(false);
+  const error = ref<Error | null>(null);
+
+  const onCompleteRef = ref(onComplete);
+  const onErrorRef = ref(onError);
+
+  let abortController: AbortController | null = null;
+
+  const clear = () => {
+    messages.value = [];
+    error.value = null;
+  };
+
+  const send = async (text: string): Promise<void> => {
+    if (!text.trim()) return;
+
+    // Abort any existing request
+    abortController?.abort();
+    abortController = new AbortController();
+
+    const userMessage: ChatMessage = {
+      id: generateChatId(),
+      role: "user",
+      text: text.trim(),
+      spec: null,
+    };
+
+    const assistantId = generateChatId();
+    const assistantMessage: ChatMessage = {
+      id: assistantId,
+      role: "assistant",
+      text: "",
+      spec: null,
+    };
+
+    // Append user message and empty assistant placeholder
+    messages.value = [...messages.value, userMessage, assistantMessage];
+    isStreaming.value = true;
+    error.value = null;
+
+    // Build messages array for the API (full conversation history + new message).
+    // Vue refs are always current — no stale closure issue unlike React useRef.
+    const historyForApi = [
+      ...messages.value
+        .filter((m) => m.id !== assistantId)
+        .map((m) => ({ role: m.role, content: m.text })),
+      { role: "user" as const, content: text.trim() },
+    ];
+
+    // Mutable state for accumulating the assistant response
+    let accumulatedText = "";
+    let currentSpec: Spec = { root: "", elements: {} };
+    let hasSpec = false;
+
+    try {
+      const response = await fetch(api, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ messages: historyForApi }),
+        signal: abortController.signal,
+      });
+
+      if (!response.ok) {
+        let errorMessage = `HTTP error: ${response.status}`;
+        try {
+          const errorData = await response.json();
+          if (errorData.message) {
+            errorMessage = errorData.message;
+          } else if (errorData.error) {
+            errorMessage = errorData.error;
+          }
+        } catch {
+          // Ignore JSON parsing errors
+        }
+        throw new Error(errorMessage);
+      }
+
+      const reader = response.body?.getReader();
+      if (!reader) {
+        throw new Error("No response body");
+      }
+
+      const decoder = new TextDecoder();
+
+      // Use createMixedStreamParser to classify lines
+      const parser = createMixedStreamParser({
+        onPatch(patch) {
+          hasSpec = true;
+          applySpecPatch(currentSpec, patch);
+          messages.value = messages.value.map((m) =>
+            m.id === assistantId
+              ? {
+                  ...m,
+                  spec: {
+                    root: currentSpec.root,
+                    elements: { ...currentSpec.elements },
+                    ...(currentSpec.state
+                      ? { state: { ...currentSpec.state } }
+                      : {}),
+                  },
+                }
+              : m,
+          );
+        },
+        onText(line) {
+          accumulatedText += (accumulatedText ? "\n" : "") + line;
+          messages.value = messages.value.map((m) =>
+            m.id === assistantId ? { ...m, text: accumulatedText } : m,
+          );
+        },
+      });
+
+      while (true) {
+        const { done, value } = await reader.read();
+        if (done) break;
+        parser.push(decoder.decode(value, { stream: true }));
+      }
+      parser.flush();
+
+      // Build final message for onComplete callback
+      const finalMessage: ChatMessage = {
+        id: assistantId,
+        role: "assistant",
+        text: accumulatedText,
+        spec: hasSpec
+          ? {
+              root: currentSpec.root,
+              elements: { ...currentSpec.elements },
+              ...(currentSpec.state ? { state: { ...currentSpec.state } } : {}),
+            }
+          : null,
+      };
+      onCompleteRef.value?.(finalMessage);
+    } catch (err) {
+      if ((err as Error).name === "AbortError") {
+        return;
+      }
+      const resolvedError = err instanceof Error ? err : new Error(String(err));
+      error.value = resolvedError;
+      // Remove empty assistant message on error
+      messages.value = messages.value.filter(
+        (m) => m.id !== assistantId || m.text.length > 0,
+      );
+      onErrorRef.value?.(resolvedError);
+    } finally {
+      isStreaming.value = false;
+    }
+  };
+
+  // Cleanup on unmount
+  onUnmounted(() => {
+    abortController?.abort();
+  });
+
+  return {
+    messages,
+    isStreaming,
+    error,
+    send,
+    clear,
+  };
+}

packages/vue/src/index.ts

@@ -0,0 +1,99 @@
+// Composables & Providers
+export {
+  StateProvider,
+  useStateStore,
+  useStateValue,
+  useStateBinding,
+  type StateContextValue,
+  type StateProviderProps,
+} from "./composables/state";
+
+export {
+  VisibilityProvider,
+  useVisibility,
+  useIsVisible,
+  type VisibilityContextValue,
+} from "./composables/visibility";
+
+export {
+  ActionProvider,
+  useActions,
+  useAction,
+  ConfirmDialog,
+  type ActionContextValue,
+  type ActionProviderProps,
+  type PendingConfirmation,
+  type ConfirmDialogProps,
+} from "./composables/actions";
+
+export {
+  ValidationProvider,
+  useOptionalValidation,
+  useValidation,
+  useFieldValidation,
+  type ValidationContextValue,
+  type ValidationProviderProps,
+  type FieldValidationState,
+} from "./composables/validation";
+
+export {
+  RepeatScopeProvider,
+  useRepeatScope,
+  type RepeatScopeValue,
+} from "./composables/repeat-scope";
+
+// Schema
+export { schema, type VueSchema, type VueSpec } from "./schema";
+
+// Core types (re-exported for convenience)
+export type { Spec, StateStore, ComputedFunction } from "@json-render/core";
+export { createStateStore } from "@json-render/core";
+
+// Catalog-aware types for Vue
+export type {
+  EventHandle,
+  BaseComponentProps,
+  SetState,
+  StateModel,
+  ComponentContext,
+  ComponentFn,
+  Components,
+  ActionFn,
+  Actions,
+} from "./catalog-types";
+
+// Hooks
+export {
+  useUIStream,
+  useChatUI,
+  useBoundProp,
+  flatToTree,
+  buildSpecFromParts,
+  getTextFromParts,
+  useJsonRenderMessage,
+  type UseUIStreamOptions,
+  type UseUIStreamReturn,
+  type UseChatUIOptions,
+  type UseChatUIReturn,
+  type ChatMessage,
+  type DataPart,
+  type TokenUsage,
+} from "./hooks";
+
+// Renderer
+export {
+  // Registry
+  defineRegistry,
+  type DefineRegistryResult,
+  // createRenderer (higher-level, includes providers)
+  createRenderer,
+  type CreateRendererProps,
+  type ComponentMap,
+  // Low-level
+  Renderer,
+  JSONUIProvider,
+  type ComponentRenderProps,
+  type ComponentRegistry,
+  type RendererProps,
+  type JSONUIProviderProps,
+} from "./renderer";

packages/vue/src/renderer.test.ts

@@ -0,0 +1,200 @@
+import { describe, it, expect, vi } from "vitest";
+import { defineComponent, h, type Component } from "vue";
+import { mount } from "@vue/test-utils";
+import type { Spec } from "@json-render/core";
+import { StateProvider } from "./composables/state";
+import { VisibilityProvider } from "./composables/visibility";
+import { ActionProvider } from "./composables/actions";
+import { ValidationProvider } from "./composables/validation";
+import { Renderer, defineRegistry, type ComponentRegistry } from "./renderer";
+
+// ---------------------------------------------------------------------------
+// Minimal test catalog and registry
+// ---------------------------------------------------------------------------
+
+// defineRegistry ignores the catalog object at runtime — use any cast
+const catalog = {} as any;
+
+const { registry } = defineRegistry(catalog, {
+  components: {
+    Card: ({ props, children }) => {
+      const p = props as Record<string, unknown>;
+      return h(
+        "div",
+        { "data-type": "card", "data-title": String(p["title"] ?? "") },
+        [String(p["title"] ?? ""), children],
+      );
+    },
+    Button: ({ props, emit }) => {
+      const p = props as Record<string, unknown>;
+      return h(
+        "button",
+        { "data-type": "button", onClick: () => emit("press") },
+        String(p["label"] ?? ""),
+      );
+    },
+  },
+});
+
+// ---------------------------------------------------------------------------
+// Mount helper: wraps in the full provider chain required by ElementRenderer
+// ---------------------------------------------------------------------------
+
+function mountRenderer(
+  spec: Spec | null,
+  reg: ComponentRegistry = registry,
+  extraProps: Record<string, unknown> = {},
+  handlers: Record<
+    string,
+    (params: Record<string, unknown>) => Promise<void>
+  > = {},
+  initialState: Record<string, unknown> = {},
+) {
+  return mount(StateProvider as Component, {
+    props: { initialState } as any,
+    slots: {
+      default: () =>
+        h(VisibilityProvider as Component, null, {
+          default: () =>
+            h(ValidationProvider as Component, null, {
+              default: () =>
+                h(ActionProvider as Component, { handlers } as any, {
+                  default: () =>
+                    h(Renderer, { spec, registry: reg, ...extraProps }),
+                }),
+            }),
+        }),
+    },
+  });
+}
+
+// ---------------------------------------------------------------------------
+// defineRegistry tests
+// ---------------------------------------------------------------------------
+
+describe("defineRegistry", () => {
+  it("wraps a render function and returns a Vue component", () => {
+    const result = defineRegistry(catalog, {
+      components: {
+        MyComp: () => h("span", null, "hello"),
+      },
+    });
+    expect(result.registry).toBeDefined();
+    expect(result.registry["MyComp"]).toBeDefined();
+  });
+
+  it("component receives resolved props from the spec element", () => {
+    const spec: Spec = {
+      root: "btn1",
+      elements: {
+        btn1: { type: "Button", props: { label: "Press me" } },
+      },
+    };
+    const wrapper = mountRenderer(spec);
+    expect(wrapper.find("[data-type='button']").text()).toBe("Press me");
+  });
+
+  it("children is passed for container components", () => {
+    const spec: Spec = {
+      root: "card1",
+      elements: {
+        card1: {
+          type: "Card",
+          props: { title: "My Card" },
+          children: ["btn1"],
+        },
+        btn1: { type: "Button", props: { label: "Click" } },
+      },
+    };
+    const wrapper = mountRenderer(spec);
+    expect(wrapper.find("[data-type='card']").exists()).toBe(true);
+    expect(wrapper.find("[data-type='button']").exists()).toBe(true);
+  });
+
+  it("emit('press') fires the corresponding on.press action", async () => {
+    const handler = vi.fn().mockResolvedValue(undefined);
+    const spec: Spec = {
+      root: "btn1",
+      elements: {
+        btn1: {
+          type: "Button",
+          props: { label: "Click" },
+          on: { press: { action: "myAction" } },
+        },
+      },
+    };
+    const wrapper = mountRenderer(spec, registry, {}, { myAction: handler });
+    await wrapper.find("[data-type='button']").trigger("click");
+    expect(handler).toHaveBeenCalledOnce();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Renderer tests
+// ---------------------------------------------------------------------------
+
+describe("Renderer", () => {
+  it("renders a single-element spec", () => {
+    const spec: Spec = {
+      root: "btn1",
+      elements: {
+        btn1: { type: "Button", props: { label: "Go" } },
+      },
+    };
+    const wrapper = mountRenderer(spec);
+    expect(wrapper.find("[data-type='button']").exists()).toBe(true);
+    expect(wrapper.find("[data-type='button']").text()).toBe("Go");
+  });
+
+  it("renders a nested spec (parent contains a child by key reference)", () => {
+    const spec: Spec = {
+      root: "card1",
+      elements: {
+        card1: {
+          type: "Card",
+          props: { title: "Root" },
+          children: ["btn1"],
+        },
+        btn1: { type: "Button", props: { label: "Action" } },
+      },
+    };
+    const wrapper = mountRenderer(spec);
+    const card = wrapper.find("[data-type='card']");
+    expect(card.exists()).toBe(true);
+    expect(card.find("[data-type='button']").exists()).toBe(true);
+  });
+
+  it("uses fallback component for unknown element types", () => {
+    const fallback = defineComponent({
+      setup() {
+        return () => h("span", { "data-type": "fallback" }, "fallback");
+      },
+    });
+    const spec: Spec = {
+      root: "el1",
+      elements: {
+        el1: { type: "Unknown", props: {} },
+      },
+    };
+    const wrapper = mountRenderer(spec, registry, { fallback });
+    expect(wrapper.find("[data-type='fallback']").exists()).toBe(true);
+  });
+
+  it("passes loading prop through to registered components", () => {
+    let receivedLoading: boolean | undefined;
+    const { registry: testRegistry } = defineRegistry(catalog, {
+      components: {
+        Widget: ({ loading }) => {
+          receivedLoading = loading;
+          return h("div", null, "widget");
+        },
+      },
+    });
+    const spec: Spec = {
+      root: "w1",
+      elements: { w1: { type: "Widget", props: {} } },
+    };
+    mountRenderer(spec, testRegistry, { loading: true });
+    expect(receivedLoading).toBe(true);
+  });
+});

packages/vue/src/renderer.ts

@@ -0,0 +1,961 @@
+import {
+  computed,
+  defineComponent,
+  h,
+  inject,
+  onErrorCaptured,
+  provide,
+  ref,
+  watch,
+  type Component,
+  type ComputedRef,
+  type PropType,
+  type VNode,
+} from "vue";
+import type {
+  UIElement,
+  Spec,
+  ActionBinding,
+  Catalog,
+  ComputedFunction,
+  SchemaDefinition,
+  StateStore,
+} from "@json-render/core";
+import {
+  resolveElementProps,
+  resolveBindings,
+  resolveActionParam,
+  evaluateVisibility,
+  getByPath,
+  type PropResolutionContext,
+} from "@json-render/core";
+import type {
+  Components,
+  Actions,
+  ActionFn,
+  SetState,
+  StateModel,
+  CatalogHasActions,
+  EventHandle,
+} from "./catalog-types";
+import { useVisibility } from "./composables/visibility";
+import { useActions } from "./composables/actions";
+import { useStateStore } from "./composables/state";
+import { StateProvider } from "./composables/state";
+import { VisibilityProvider } from "./composables/visibility";
+import { ActionProvider } from "./composables/actions";
+import { ValidationProvider } from "./composables/validation";
+import { ConfirmDialog } from "./composables/actions";
+import {
+  RepeatScopeProvider,
+  useRepeatScope,
+} from "./composables/repeat-scope";
+
+/**
+ * Props passed to component renderers
+ */
+export interface ComponentRenderProps<P = Record<string, unknown>> {
+  /** The element being rendered */
+  element: UIElement<string, P>;
+  /** Emit a named event */
+  emit: (event: string) => void;
+  /** Get an event handle with metadata */
+  on: (event: string) => EventHandle;
+  /**
+   * Two-way binding paths resolved from `$bindState` / `$bindItem` expressions.
+   * Maps prop name → absolute state path for write-back.
+   */
+  bindings?: Record<string, string>;
+  /** Whether the parent is loading */
+  loading?: boolean;
+}
+
+/**
+ * Registry of component renderers (Vue component definitions)
+ */
+export type ComponentRegistry = Record<string, Component>;
+
+/**
+ * Props for the Renderer component
+ */
+export interface RendererProps {
+  spec: Spec | null;
+  registry: ComponentRegistry;
+  loading?: boolean;
+  fallback?: Component;
+}
+
+// ---------------------------------------------------------------------------
+// FunctionsContext — provides $computed functions to the element tree
+// ---------------------------------------------------------------------------
+
+const EMPTY_FUNCTIONS: Record<string, ComputedFunction> = {};
+const FUNCTIONS_KEY = Symbol("json-render:functions");
+
+const FunctionsProvider = defineComponent({
+  name: "FunctionsProvider",
+  props: {
+    functions: {
+      type: Object as PropType<Record<string, ComputedFunction>>,
+      default: undefined,
+    },
+  },
+  setup(props, { slots }) {
+    const fns = computed(() => props.functions ?? EMPTY_FUNCTIONS);
+    provide(FUNCTIONS_KEY, fns);
+    return () => slots.default?.();
+  },
+});
+
+function useFunctions(): ComputedRef<Record<string, ComputedFunction>> {
+  return inject<ComputedRef<Record<string, ComputedFunction>>>(
+    FUNCTIONS_KEY,
+    computed(() => EMPTY_FUNCTIONS),
+  );
+}
+
+// ---------------------------------------------------------------------------
+// ElementErrorBoundary — catches rendering errors in individual elements
+// ---------------------------------------------------------------------------
+
+const ElementErrorBoundary = defineComponent({
+  name: "ElementErrorBoundary",
+  props: {
+    elementType: {
+      type: String,
+      required: true,
+    },
+  },
+  setup(props, { slots }) {
+    const hasError = ref(false);
+
+    onErrorCaptured((error) => {
+      console.error(
+        `[json-render] Rendering error in <${props.elementType}>:`,
+        error,
+      );
+      hasError.value = true;
+      return false; // prevent propagation
+    });
+
+    return () => {
+      if (hasError.value) return null;
+      return slots.default?.();
+    };
+  },
+});
+
+// ---------------------------------------------------------------------------
+// resolveAndExecuteBindings — shared helper for emitEvent / watch handlers
+// ---------------------------------------------------------------------------
+
+async function resolveAndExecuteBindings(
+  actionBindings: ActionBinding[],
+  ctx: PropResolutionContext,
+  getSnapshot: () => Record<string, unknown>,
+  execute: (binding: ActionBinding) => Promise<void>,
+  cancelled?: () => boolean,
+): Promise<void> {
+  for (const b of actionBindings) {
+    if (cancelled?.()) break;
+    if (!b.params) {
+      await execute(b);
+      if (cancelled?.()) break;
+      continue;
+    }
+    const liveCtx: PropResolutionContext = {
+      ...ctx,
+      stateModel: getSnapshot(),
+    };
+    const resolved: Record<string, unknown> = {};
+    for (const [key, val] of Object.entries(b.params)) {
+      resolved[key] = resolveActionParam(val, liveCtx);
+    }
+    await execute({ ...b, params: resolved });
+    if (cancelled?.()) break;
+  }
+}
+
+// ---------------------------------------------------------------------------
+// ElementRenderer — renders a single element from the spec
+// ---------------------------------------------------------------------------
+
+interface ElementRendererInternalProps {
+  element: UIElement;
+  spec: Spec;
+  registry: ComponentRegistry;
+  loading?: boolean;
+  fallback?: Component;
+}
+
+const ElementRenderer = defineComponent({
+  name: "JsonRenderElement",
+  props: {
+    element: {
+      type: Object as PropType<UIElement>,
+      required: true,
+    },
+    spec: {
+      type: Object as PropType<Spec>,
+      required: true,
+    },
+    registry: {
+      type: Object as PropType<ComponentRegistry>,
+      required: true,
+    },
+    loading: {
+      type: Boolean,
+      default: undefined,
+    },
+    fallback: {
+      type: Object as PropType<Component>,
+      default: undefined,
+    },
+  },
+  setup(props: ElementRendererInternalProps) {
+    const repeatScope = useRepeatScope();
+    const { ctx: visibilityCtx } = useVisibility();
+    const { execute } = useActions();
+    const { getSnapshot, state: watchState } = useStateStore();
+    const functions = useFunctions();
+
+    // Build context with repeat scope and $computed functions
+    const fullCtx = computed<PropResolutionContext>(() => {
+      const base: PropResolutionContext = repeatScope
+        ? {
+            ...visibilityCtx.value,
+            repeatItem: repeatScope.item,
+            repeatIndex: repeatScope.index,
+            repeatBasePath: repeatScope.basePath,
+          }
+        : { ...visibilityCtx.value };
+      base.functions = functions.value;
+      return base;
+    });
+
+    // Create emit function
+    const emitEvent = async (eventName: string): Promise<void> => {
+      const binding = props.element.on?.[eventName];
+      if (!binding) return;
+      const actionBindings = Array.isArray(binding) ? binding : [binding];
+      await resolveAndExecuteBindings(
+        actionBindings,
+        fullCtx.value,
+        getSnapshot,
+        execute,
+      );
+    };
+
+    // Create on() function
+    const onEvent = (eventName: string): EventHandle => {
+      const binding = props.element.on?.[eventName];
+      if (!binding) {
+        return { emit: () => {}, shouldPreventDefault: false, bound: false };
+      }
+      const actionBindings = Array.isArray(binding) ? binding : [binding];
+      const shouldPreventDefault = actionBindings.some((b) => b.preventDefault);
+      return {
+        emit: () => {
+          void emitEvent(eventName);
+        },
+        shouldPreventDefault,
+        bound: true,
+      };
+    };
+
+    // Watch effect: fire actions when watched state paths change.
+    const watchedValues = computed(() => {
+      const cfg = props.element.watch;
+      if (!cfg) return undefined;
+      const values: Record<string, unknown> = {};
+      for (const path of Object.keys(cfg)) {
+        values[path] = getByPath(watchState.value, path);
+      }
+      return values;
+    });
+
+    watch(
+      watchedValues,
+      (current, prev, onCleanup) => {
+        const cfg = props.element.watch;
+        if (!cfg || !current) return;
+
+        let cancelled = false;
+        onCleanup(() => {
+          cancelled = true;
+        });
+
+        const paths = Object.keys(cfg);
+        void (async () => {
+          for (const path of paths) {
+            if (cancelled) break;
+            if (prev && current[path] === prev[path]) continue;
+            const binding = cfg[path];
+            if (!binding) continue;
+            const bindings = Array.isArray(binding) ? binding : [binding];
+            await resolveAndExecuteBindings(
+              bindings,
+              fullCtx.value,
+              getSnapshot,
+              execute,
+              () => cancelled,
+            );
+          }
+        })().catch(console.error);
+      },
+      { deep: true },
+    );
+
+    return () => {
+      const ctx = fullCtx.value;
+
+      // Evaluate visibility
+      const isVisible =
+        props.element.visible === undefined
+          ? true
+          : evaluateVisibility(props.element.visible, ctx);
+
+      if (!isVisible) return null;
+
+      // Resolve bindings and props
+      const rawProps = props.element.props as Record<string, unknown>;
+      const elementBindings = resolveBindings(rawProps, ctx);
+      const resolvedProps = resolveElementProps(rawProps, ctx);
+
+      const resolvedElement =
+        resolvedProps !== props.element.props
+          ? { ...props.element, props: resolvedProps }
+          : props.element;
+
+      // Get component from registry
+      const Component = props.registry[resolvedElement.type] ?? props.fallback;
+
+      if (!Component) {
+        console.warn(
+          `[json-render] No renderer for component type: ${resolvedElement.type}`,
+        );
+        return null;
+      }
+
+      // Render children
+      const childrenVNodes: VNode | VNode[] | undefined = resolvedElement.repeat
+        ? h(RepeatChildren, {
+            element: resolvedElement,
+            spec: props.spec,
+            registry: props.registry,
+            loading: props.loading,
+            fallback: props.fallback,
+          })
+        : (resolvedElement.children
+            ?.map((childKey) => {
+              const childElement = props.spec.elements[childKey];
+              if (!childElement) {
+                if (!props.loading) {
+                  console.warn(
+                    `[json-render] Missing element "${childKey}" referenced as child of "${resolvedElement.type}". This element will not render.`,
+                  );
+                }
+                return null;
+              }
+              return h(ElementRenderer, {
+                key: childKey,
+                element: childElement,
+                spec: props.spec,
+                registry: props.registry,
+                loading: props.loading,
+                fallback: props.fallback,
+              });
+            })
+            .filter((n): n is VNode => n !== null) ?? undefined);
+
+      return h(
+        ElementErrorBoundary,
+        { elementType: resolvedElement.type },
+        {
+          default: () =>
+            h(
+              Component,
+              {
+                element: resolvedElement,
+                emit: emitEvent,
+                on: onEvent,
+                bindings: elementBindings,
+                loading: props.loading,
+              },
+              { default: () => childrenVNodes },
+            ),
+        },
+      );
+    };
+  },
+});
+
+// ---------------------------------------------------------------------------
+// RepeatChildren — renders child elements once per item in a state array
+// ---------------------------------------------------------------------------
+
+const RepeatChildren = defineComponent({
+  name: "JsonRenderRepeatChildren",
+  props: {
+    element: {
+      type: Object as PropType<UIElement>,
+      required: true,
+    },
+    spec: {
+      type: Object as PropType<Spec>,
+      required: true,
+    },
+    registry: {
+      type: Object as PropType<ComponentRegistry>,
+      required: true,
+    },
+    loading: {
+      type: Boolean,
+      default: undefined,
+    },
+    fallback: {
+      type: Object as PropType<Component>,
+      default: undefined,
+    },
+  },
+  setup(props) {
+    const { state } = useStateStore();
+
+    return () => {
+      const repeat = props.element.repeat;
+      if (!repeat?.statePath) return null;
+      const statePath = repeat.statePath;
+      const raw = getByPath(state.value, statePath);
+      const items = Array.isArray(raw) ? (raw as unknown[]) : [];
+
+      return items.map((itemValue, index) => {
+        const key =
+          repeat.key && typeof itemValue === "object" && itemValue !== null
+            ? String(
+                (itemValue as Record<string, unknown>)[repeat.key] ?? index,
+              )
+            : String(index);
+
+        return h(
+          RepeatScopeProvider,
+          { key, item: itemValue, index, basePath: `${statePath}/${index}` },
+          {
+            default: () =>
+              props.element.children
+                ?.map((childKey) => {
+                  const childElement = props.spec.elements[childKey];
+                  if (!childElement) {
+                    if (!props.loading) {
+                      console.warn(
+                        `[json-render] Missing element "${childKey}" referenced as child of "${props.element.type}" (repeat). This element will not render.`,
+                      );
+                    }
+                    return null;
+                  }
+                  return h(ElementRenderer, {
+                    key: childKey,
+                    element: childElement,
+                    spec: props.spec,
+                    registry: props.registry,
+                    loading: props.loading,
+                    fallback: props.fallback,
+                  });
+                })
+                .filter((n): n is VNode => n !== null) ?? null,
+          },
+        );
+      });
+    };
+  },
+});
+
+// ---------------------------------------------------------------------------
+// Renderer — main exported component
+// ---------------------------------------------------------------------------
+
+/**
+ * Main renderer component
+ */
+export const Renderer = defineComponent({
+  name: "JsonRenderer",
+  props: {
+    spec: {
+      type: Object as PropType<Spec | null>,
+      default: null,
+    },
+    registry: {
+      type: Object as PropType<ComponentRegistry>,
+      required: true,
+    },
+    loading: {
+      type: Boolean,
+      default: undefined,
+    },
+    fallback: {
+      type: Object as PropType<Component>,
+      default: undefined,
+    },
+  },
+  setup(props) {
+    return () => {
+      if (!props.spec?.root) return null;
+
+      const rootElement = props.spec.elements[props.spec.root];
+      if (!rootElement) return null;
+
+      return h(ElementRenderer, {
+        element: rootElement,
+        spec: props.spec,
+        registry: props.registry,
+        loading: props.loading,
+        fallback: props.fallback,
+      });
+    };
+  },
+});
+
+// ---------------------------------------------------------------------------
+// ConfirmationDialogManager
+// ---------------------------------------------------------------------------
+
+const ConfirmationDialogManager = defineComponent({
+  name: "ConfirmationDialogManager",
+  setup() {
+    const { pendingConfirmation, confirm, cancel } = useActions();
+
+    return () => {
+      if (!pendingConfirmation?.action.confirm) return null;
+
+      return h(ConfirmDialog, {
+        confirm: pendingConfirmation.action.confirm,
+        onConfirm: confirm,
+        onCancel: cancel,
+      });
+    };
+  },
+});
+
+// ---------------------------------------------------------------------------
+// JSONUIProvider — combined provider for all contexts
+// ---------------------------------------------------------------------------
+
+/**
+ * Props for JSONUIProvider
+ */
+export interface JSONUIProviderProps {
+  registry: ComponentRegistry;
+  store?: StateStore;
+  initialState?: Record<string, unknown>;
+  handlers?: Record<
+    string,
+    (params: Record<string, unknown>) => Promise<unknown> | unknown
+  >;
+  navigate?: (path: string) => void;
+  validationFunctions?: Record<
+    string,
+    (value: unknown, args?: Record<string, unknown>) => boolean
+  >;
+  /** Named functions for `$computed` expressions in props */
+  functions?: Record<string, ComputedFunction>;
+  onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
+}
+
+/**
+ * Combined provider for all JSONUI contexts
+ */
+export const JSONUIProvider = defineComponent({
+  name: "JSONUIProvider",
+  props: {
+    registry: {
+      type: Object as PropType<ComponentRegistry>,
+      required: true,
+    },
+    store: {
+      type: Object as PropType<StateStore>,
+      default: undefined,
+    },
+    initialState: {
+      type: Object as PropType<Record<string, unknown>>,
+      default: undefined,
+    },
+    handlers: {
+      type: Object as PropType<
+        Record<
+          string,
+          (params: Record<string, unknown>) => Promise<unknown> | unknown
+        >
+      >,
+      default: undefined,
+    },
+    navigate: {
+      type: Function as PropType<(path: string) => void>,
+      default: undefined,
+    },
+    validationFunctions: {
+      type: Object as PropType<
+        Record<
+          string,
+          (value: unknown, args?: Record<string, unknown>) => boolean
+        >
+      >,
+      default: undefined,
+    },
+    functions: {
+      type: Object as PropType<Record<string, ComputedFunction>>,
+      default: undefined,
+    },
+    onStateChange: {
+      type: Function as PropType<
+        (changes: Array<{ path: string; value: unknown }>) => void
+      >,
+      default: undefined,
+    },
+  },
+  setup(props, { slots }) {
+    return () =>
+      h(
+        StateProvider,
+        {
+          store: props.store,
+          initialState: props.initialState,
+          onStateChange: props.onStateChange,
+        },
+        {
+          default: () =>
+            h(VisibilityProvider, null, {
+              default: () =>
+                h(
+                  ValidationProvider,
+                  { customFunctions: props.validationFunctions },
+                  {
+                    default: () =>
+                      h(
+                        ActionProvider,
+                        { handlers: props.handlers, navigate: props.navigate },
+                        {
+                          default: () =>
+                            h(
+                              FunctionsProvider,
+                              { functions: props.functions },
+                              {
+                                default: () => [
+                                  slots.default?.(),
+                                  h(ConfirmationDialogManager),
+                                ],
+                              },
+                            ),
+                        },
+                      ),
+                  },
+                ),
+            }),
+        },
+      );
+  },
+});
+
+// ============================================================================
+// defineRegistry
+// ============================================================================
+
+/**
+ * Result returned by defineRegistry
+ */
+export interface DefineRegistryResult {
+  registry: ComponentRegistry;
+  handlers: (
+    getSetState: () => SetState | undefined,
+    getState: () => StateModel,
+  ) => Record<string, (params: Record<string, unknown>) => Promise<void>>;
+  executeAction: (
+    actionName: string,
+    params: Record<string, unknown> | undefined,
+    setState: SetState,
+    state?: StateModel,
+  ) => Promise<void>;
+}
+
+type DefineRegistryOptions<C extends Catalog> = {
+  components?: Components<C>;
+} & (CatalogHasActions<C> extends true
+  ? { actions: Actions<C> }
+  : { actions?: Actions<C> });
+
+type DefineRegistryComponentFn = (ctx: {
+  props: unknown;
+  children?: VNode | VNode[];
+  emit: (event: string) => void;
+  on: (event: string) => EventHandle;
+  bindings?: Record<string, string>;
+  loading?: boolean;
+}) => VNode | VNode[] | null | string;
+
+type DefineRegistryActionFn = (
+  params: Record<string, unknown> | undefined,
+  setState: SetState,
+  state: StateModel,
+) => Promise<void>;
+
+/**
+ * Create a registry from a catalog with components and/or actions.
+ *
+ * @example
+ * ```ts
+ * // Components only
+ * const { registry } = defineRegistry(catalog, {
+ *   components: {
+ *     Card: ({ props, children }) => h('div', { class: 'card' }, [props.title, children]),
+ *   },
+ * });
+ *
+ * // Both
+ * const { registry, handlers, executeAction } = defineRegistry(catalog, {
+ *   components: { ... },
+ *   actions: { ... },
+ * });
+ * ```
+ */
+export function defineRegistry<C extends Catalog>(
+  _catalog: C,
+  options: DefineRegistryOptions<C>,
+): DefineRegistryResult {
+  const registry: ComponentRegistry = {};
+
+  if (options.components) {
+    for (const [name, componentFn] of Object.entries(options.components)) {
+      registry[name] = defineComponent({
+        name: `JsonRenderRegistry_${name}`,
+        props: {
+          element: {
+            type: Object as PropType<UIElement>,
+            required: true,
+          },
+          emit: {
+            type: Function as PropType<(event: string) => void>,
+            required: true,
+          },
+          on: {
+            type: Function as PropType<(event: string) => EventHandle>,
+            required: true,
+          },
+          bindings: {
+            type: Object as PropType<Record<string, string>>,
+            default: undefined,
+          },
+          loading: {
+            type: Boolean,
+            default: undefined,
+          },
+        },
+        setup(registryProps, { slots }) {
+          return () =>
+            (componentFn as DefineRegistryComponentFn)({
+              props: registryProps.element.props,
+              children: slots.default?.(),
+              emit: registryProps.emit,
+              on: registryProps.on,
+              bindings: registryProps.bindings,
+              loading: registryProps.loading,
+            });
+        },
+      });
+    }
+  }
+
+  const actionMap = options.actions
+    ? (Object.entries(options.actions) as Array<
+        [string, DefineRegistryActionFn]
+      >)
+    : [];
+
+  const handlers = (
+    getSetState: () => SetState | undefined,
+    getState: () => StateModel,
+  ): Record<string, (params: Record<string, unknown>) => Promise<void>> => {
+    const result: Record<
+      string,
+      (params: Record<string, unknown>) => Promise<void>
+    > = {};
+    for (const [name, actionFn] of actionMap) {
+      result[name] = async (params) => {
+        const setState = getSetState();
+        const state = getState();
+        if (setState) {
+          await actionFn(params, setState, state);
+        }
+      };
+    }
+    return result;
+  };
+
+  const executeAction = async (
+    actionName: string,
+    params: Record<string, unknown> | undefined,
+    setState: SetState,
+    state: StateModel = {},
+  ): Promise<void> => {
+    const entry = actionMap.find(([name]) => name === actionName);
+    if (entry) {
+      await entry[1](params, setState, state);
+    } else {
+      console.warn(`Unknown action: ${actionName}`);
+    }
+  };
+
+  return { registry, handlers, executeAction };
+}
+
+// ============================================================================
+// createRenderer
+// ============================================================================
+
+/**
+ * Props for renderers created with createRenderer
+ */
+export interface CreateRendererProps {
+  spec: Spec | null;
+  store?: StateStore;
+  state?: Record<string, unknown>;
+  onAction?: (actionName: string, params?: Record<string, unknown>) => void;
+  onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
+  /** Named functions for `$computed` expressions in props */
+  functions?: Record<string, ComputedFunction>;
+  loading?: boolean;
+  fallback?: Component;
+}
+
+/**
+ * Component map type — maps component names to Vue components
+ */
+export type ComponentMap<
+  TComponents extends Record<string, { props: unknown }>,
+> = {
+  [K in keyof TComponents]: Component;
+};
+
+/**
+ * Create a renderer from a catalog
+ *
+ * @example
+ * ```typescript
+ * const DashboardRenderer = createRenderer(dashboardCatalog, {
+ *   Card: ({ props, children }) => h('div', { class: 'card' }, children),
+ *   Metric: ({ props }) => h('span', null, props.value),
+ * });
+ *
+ * // Usage in template
+ * <DashboardRenderer :spec="aiGeneratedSpec" :state="state" />
+ * ```
+ */
+export function createRenderer<
+  TDef extends SchemaDefinition,
+  TCatalog extends { components: Record<string, { props: unknown }> },
+>(
+  catalog: Catalog<TDef, TCatalog>,
+  components: ComponentMap<TCatalog["components"]>,
+): Component {
+  const registry: ComponentRegistry =
+    components as unknown as ComponentRegistry;
+
+  return defineComponent({
+    name: "CatalogRenderer",
+    props: {
+      spec: {
+        type: Object as PropType<Spec | null>,
+        default: null,
+      },
+      store: {
+        type: Object as PropType<StateStore>,
+        default: undefined,
+      },
+      state: {
+        type: Object as PropType<Record<string, unknown>>,
+        default: undefined,
+      },
+      onAction: {
+        type: Function as PropType<
+          (actionName: string, params?: Record<string, unknown>) => void
+        >,
+        default: undefined,
+      },
+      onStateChange: {
+        type: Function as PropType<
+          (changes: Array<{ path: string; value: unknown }>) => void
+        >,
+        default: undefined,
+      },
+      functions: {
+        type: Object as PropType<Record<string, ComputedFunction>>,
+        default: undefined,
+      },
+      loading: {
+        type: Boolean,
+        default: undefined,
+      },
+      fallback: {
+        type: Object as PropType<Component>,
+        default: undefined,
+      },
+    },
+    setup(rendererProps) {
+      return () => {
+        // Build the action handlers proxy if onAction is provided
+        const actionHandlers = rendererProps.onAction
+          ? new Proxy(
+              {} as Record<
+                string,
+                (params: Record<string, unknown>) => void | Promise<void>
+              >,
+              {
+                get: (_target, prop: string) => {
+                  return (params: Record<string, unknown>) =>
+                    rendererProps.onAction!(prop, params);
+                },
+                has: () => true,
+              },
+            )
+          : undefined;
+
+        return h(
+          StateProvider,
+          {
+            store: rendererProps.store,
+            initialState: rendererProps.state,
+            onStateChange: rendererProps.onStateChange,
+          },
+          {
+            default: () =>
+              h(VisibilityProvider, null, {
+                default: () =>
+                  h(ValidationProvider, null, {
+                    default: () =>
+                      h(
+                        ActionProvider,
+                        { handlers: actionHandlers },
+                        {
+                          default: () =>
+                            h(
+                              FunctionsProvider,
+                              { functions: rendererProps.functions },
+                              {
+                                default: () => [
+                                  h(Renderer, {
+                                    spec: rendererProps.spec,
+                                    registry,
+                                    loading: rendererProps.loading,
+                                    fallback: rendererProps.fallback,
+                                  }),
+                                  h(ConfirmationDialogManager),
+                                ],
+                              },
+                            ),
+                        },
+                      ),
+                  }),
+              }),
+          },
+        );
+      };
+    },
+  });
+}

packages/vue/src/schema.ts

@@ -0,0 +1,109 @@
+import { defineSchema } from "@json-render/core";
+
+/**
+ * The schema for @json-render/vue
+ *
+ * Defines:
+ * - Spec: A flat tree of elements with keys, types, props, and children references
+ * - Catalog: Components with props schemas, and optional actions
+ */
+export const schema = defineSchema(
+  (s) => ({
+    // What the AI-generated SPEC looks like
+    spec: s.object({
+      /** Root element key */
+      root: s.string(),
+      /** Flat map of elements by key */
+      elements: s.record(
+        s.object({
+          /** Component type from catalog */
+          type: s.ref("catalog.components"),
+          /** Component props */
+          props: s.propsOf("catalog.components"),
+          /** Child element keys (flat reference) */
+          children: s.array(s.string()),
+          /** Visibility condition */
+          visible: s.any(),
+        }),
+      ),
+    }),
+
+    // What the CATALOG must provide
+    catalog: s.object({
+      /** Component definitions */
+      components: s.map({
+        /** Zod schema for component props */
+        props: s.zod(),
+        /** Slots for this component. Use ['default'] for children, or named slots like ['header', 'footer'] */
+        slots: s.array(s.string()),
+        /** Description for AI generation hints */
+        description: s.string(),
+        /** Example prop values used in prompt examples (auto-generated from Zod schema if omitted) */
+        example: s.any(),
+      }),
+      /** Action definitions (optional) */
+      actions: s.map({
+        /** Zod schema for action params */
+        params: s.zod(),
+        /** Description for AI generation hints */
+        description: s.string(),
+      }),
+    }),
+  }),
+  {
+    builtInActions: [
+      {
+        name: "setState",
+        description:
+          "Update a value in the state model at the given statePath. Params: { statePath: string, value: any }",
+      },
+      {
+        name: "pushState",
+        description:
+          'Append an item to an array in state. Params: { statePath: string, value: any, clearStatePath?: string }. Value can contain {"$state":"/path"} refs and "$id" for auto IDs.',
+      },
+      {
+        name: "removeState",
+        description:
+          "Remove an item from an array in state by index. Params: { statePath: string, index: number }",
+      },
+      {
+        name: "validateForm",
+        description:
+          "Validate all registered form fields and write the result to state. Params: { statePath?: string }. Defaults to /formValidation. Result: { valid: boolean, errors: Record<string, string[]> }.",
+      },
+    ],
+    defaultRules: [
+      // Element integrity
+      "CRITICAL INTEGRITY CHECK: Before outputting ANY element that references children, you MUST have already output (or will output) each child as its own element. If an element has children: ['a', 'b'], then elements 'a' and 'b' MUST exist. A missing child element causes that entire branch of the UI to be invisible.",
+      "SELF-CHECK: After generating all elements, mentally walk the tree from root. Every key in every children array must resolve to a defined element. If you find a gap, output the missing element immediately.",
+
+      // Field placement
+      'CRITICAL: The "visible" field goes on the ELEMENT object, NOT inside "props". Correct: {"type":"<ComponentName>","props":{},"visible":{"$state":"/tab","eq":"home"},"children":[...]}.',
+      'CRITICAL: The "on" field goes on the ELEMENT object, NOT inside "props". Use on.press, on.change, on.submit etc. NEVER put action/actionParams inside props.',
+
+      // State and data
+      "When the user asks for a UI that displays data (e.g. blog posts, products, users), ALWAYS include a state field with realistic sample data. The state field is a top-level field on the spec (sibling of root/elements).",
+      'When building repeating content backed by a state array (e.g. posts, products, items), use the "repeat" field on a container element. Example: { "type": "<ContainerComponent>", "props": {}, "repeat": { "statePath": "/posts", "key": "id" }, "children": ["post-card"] }. Replace <ContainerComponent> with an appropriate component from the AVAILABLE COMPONENTS list. Inside repeated children, use { "$item": "field" } to read a field from the current item, and { "$index": true } for the current array index. For two-way binding to an item field use { "$bindItem": "completed" }. Do NOT hardcode individual elements for each array item.',
+
+      // Design quality
+      "Design with visual hierarchy: use container components to group content, heading components for section titles, proper spacing, and status indicators. ONLY use components from the AVAILABLE COMPONENTS list.",
+      "For data-rich UIs, use multi-column layout components if available. For forms and single-column content, use vertical layout components. ONLY use components from the AVAILABLE COMPONENTS list.",
+      "Always include realistic, professional-looking sample data. For blogs include 3-4 posts with varied titles, authors, dates, categories. For products include names, prices, images. Never leave data empty.",
+    ],
+  },
+);
+
+/**
+ * Type for the Vue schema
+ */
+export type VueSchema = typeof schema;
+
+/**
+ * Infer the spec type from a catalog
+ */
+export type VueSpec<TCatalog> = typeof schema extends {
+  createCatalog: (catalog: TCatalog) => { _specType: infer S };
+}
+  ? S
+  : never;

packages/vue/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "extends": "@internal/typescript-config/base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": "src"
+  },
+  "include": ["src"],
+  "exclude": ["node_modules", "dist"]
+}

packages/vue/tsup.config.ts

@@ -0,0 +1,10 @@
+import { defineConfig } from "tsup";
+
+export default defineConfig({
+  entry: ["src/index.ts", "src/schema.ts"],
+  format: ["cjs", "esm"],
+  dts: true,
+  sourcemap: true,
+  clean: true,
+  external: ["vue", "@json-render/core"],
+});

packages/xstate-store/README.md

@@ -0,0 +1,43 @@
+# @json-render/xstate-store
+
+[XState Store](https://stately.ai/docs/xstate-store) adapter for json-render's `StateStore` interface. Wire an `@xstate/store` atom as the state backend for json-render.
+
+## Installation
+
+```bash
+npm install @json-render/xstate-store @json-render/core @json-render/react @xstate/store
+```
+
+> [!NOTE]
+> This adapter requires `@xstate/store` v3+.
+
+## Usage
+
+```ts
+import { createAtom } from "@xstate/store";
+import { xstateStoreStateStore } from "@json-render/xstate-store";
+import { StateProvider } from "@json-render/react";
+
+// 1. Create an atom
+const uiAtom = createAtom({ count: 0 });
+
+// 2. Create the json-render StateStore adapter
+const store = xstateStoreStateStore({ atom: uiAtom });
+
+// 3. Use it
+<StateProvider store={store}>
+  {/* json-render reads/writes go through @xstate/store */}
+</StateProvider>
+```
+
+## API
+
+### `xstateStoreStateStore(options)`
+
+Creates a `StateStore` backed by an `@xstate/store` atom.
+
+#### Options
+
+| Option | Type | Required | Description |
+|--------|------|----------|-------------|
+| `atom` | `Atom<StateModel>` | Yes | An `@xstate/store` atom (from `createAtom`) holding the json-render state model |

packages/xstate-store/package.json

@@ -0,0 +1,55 @@
+{
+  "name": "@json-render/xstate-store",
+  "version": "0.0.0",
+  "license": "Apache-2.0",
+  "description": "XState Store adapter for json-render StateStore",
+  "keywords": [
+    "json-render",
+    "xstate",
+    "xstate-store",
+    "state-management",
+    "adapter"
+  ],
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/vercel-labs/json-render.git",
+    "directory": "packages/xstate-store"
+  },
+  "homepage": "https://github.com/vercel-labs/json-render#readme",
+  "bugs": {
+    "url": "https://github.com/vercel-labs/json-render/issues"
+  },
+  "publishConfig": {
+    "access": "public"
+  },
+  "main": "./dist/index.js",
+  "module": "./dist/index.mjs",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.mjs",
+      "require": "./dist/index.js"
+    }
+  },
+  "files": [
+    "dist"
+  ],
+  "scripts": {
+    "build": "tsup",
+    "dev": "tsup --watch",
+    "check-types": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@json-render/core": "workspace:*"
+  },
+  "peerDependencies": {
+    "@xstate/store": ">=3.0.0"
+  },
+  "devDependencies": {
+    "@internal/typescript-config": "workspace:*",
+    "tsup": "^8.0.2",
+    "typescript": "^5.4.5",
+    "@xstate/store": "^3.0.0"
+  }
+}

packages/xstate-store/src/index.test.ts

@@ -0,0 +1,148 @@
+import { describe, it, expect, vi } from "vitest";
+import { createAtom } from "@xstate/store";
+import { xstateStoreStateStore } from "./index";
+
+function createTestStore(initial: Record<string, unknown> = {}) {
+  const atom = createAtom<Record<string, unknown>>(initial);
+  const store = xstateStoreStateStore({ atom });
+  return { atom, store };
+}
+
+describe("xstateStoreStateStore", () => {
+  it("get/set round-trip", () => {
+    const { store } = createTestStore({ count: 0 });
+
+    expect(store.get("/count")).toBe(0);
+
+    store.set("/count", 42);
+
+    expect(store.get("/count")).toBe(42);
+    expect(store.getSnapshot().count).toBe(42);
+  });
+
+  it("update round-trip with multiple values", () => {
+    const { store } = createTestStore({});
+
+    store.update({ "/a": 1, "/b": "hello" });
+
+    expect(store.get("/a")).toBe(1);
+    expect(store.get("/b")).toBe("hello");
+    expect(store.getSnapshot()).toEqual({ a: 1, b: "hello" });
+  });
+
+  it("subscribe fires on set", () => {
+    const { store } = createTestStore({});
+    const listener = vi.fn();
+    store.subscribe(listener);
+
+    store.set("/x", 1);
+
+    expect(listener).toHaveBeenCalledTimes(1);
+  });
+
+  it("subscribe fires on update", () => {
+    const { store } = createTestStore({});
+    const listener = vi.fn();
+    store.subscribe(listener);
+
+    store.update({ "/a": 1, "/b": 2 });
+
+    expect(listener).toHaveBeenCalledTimes(1);
+  });
+
+  it("unsubscribe stops notifications", () => {
+    const { store } = createTestStore({});
+    const listener = vi.fn();
+    const unsub = store.subscribe(listener);
+
+    store.set("/x", 1);
+    expect(listener).toHaveBeenCalledTimes(1);
+
+    unsub();
+    store.set("/x", 2);
+    expect(listener).toHaveBeenCalledTimes(1);
+  });
+
+  it("getSnapshot immutability -- previous snapshot is not mutated", () => {
+    const { store } = createTestStore({
+      user: { name: "Alice", age: 30 },
+    });
+    const snap1 = store.getSnapshot();
+
+    store.set("/user/name", "Bob");
+    const snap2 = store.getSnapshot();
+
+    expect(snap1.user).toEqual({ name: "Alice", age: 30 });
+    expect((snap2.user as Record<string, unknown>).name).toBe("Bob");
+    expect(snap1.user).not.toBe(snap2.user);
+  });
+
+  it("structural sharing -- untouched branches keep references", () => {
+    const { store } = createTestStore({
+      a: { x: 1 },
+      b: { y: 2 },
+    });
+    const snap1 = store.getSnapshot();
+
+    store.set("/a/x", 99);
+    const snap2 = store.getSnapshot();
+
+    expect(snap2.b).toBe(snap1.b);
+    expect(snap2.a).not.toBe(snap1.a);
+  });
+
+  it("getServerSnapshot returns same as getSnapshot", () => {
+    const { store } = createTestStore({ x: 1 });
+
+    expect(store.getServerSnapshot!()).toBe(store.getSnapshot());
+
+    store.set("/x", 2);
+    expect(store.getServerSnapshot!()).toBe(store.getSnapshot());
+  });
+
+  it("set skips update when value is unchanged", () => {
+    const { store } = createTestStore({ x: 1 });
+    const snap1 = store.getSnapshot();
+    const listener = vi.fn();
+    store.subscribe(listener);
+
+    store.set("/x", 1);
+
+    expect(listener).not.toHaveBeenCalled();
+    expect(store.getSnapshot()).toBe(snap1);
+  });
+
+  it("update skips update when no values changed", () => {
+    const { store } = createTestStore({ a: 1, b: 2 });
+    const snap1 = store.getSnapshot();
+    const listener = vi.fn();
+    store.subscribe(listener);
+
+    store.update({ "/a": 1, "/b": 2 });
+
+    expect(listener).not.toHaveBeenCalled();
+    expect(store.getSnapshot()).toBe(snap1);
+  });
+
+  it("reads from the shared atom", () => {
+    const atom = createAtom<Record<string, unknown>>({ count: 0 });
+    const store = xstateStoreStateStore({ atom });
+
+    atom.set({ count: 99 });
+
+    expect(store.get("/count")).toBe(99);
+    expect(store.getSnapshot().count).toBe(99);
+  });
+
+  it("subscribe fires on external atom.set", () => {
+    const atom = createAtom<Record<string, unknown>>({ count: 0 });
+    const store = xstateStoreStateStore({ atom });
+    const listener = vi.fn();
+    store.subscribe(listener);
+
+    atom.set({ count: 99 });
+
+    expect(listener).toHaveBeenCalledTimes(1);
+    expect(store.get("/count")).toBe(99);
+  });
+});

packages/xstate-store/src/index.ts

@@ -0,0 +1,45 @@
+import type { StateModel, StateStore } from "@json-render/core";
+import { createStoreAdapter } from "@json-render/core/store-utils";
+import type { Atom } from "@xstate/store";
+
+export type { StateStore } from "@json-render/core";
+
+/**
+ * Options for {@link xstateStoreStateStore}.
+ */
+export interface XstateStoreStateStoreOptions {
+  /** An `@xstate/store` atom (created with `createAtom`). */
+  atom: Atom<StateModel>;
+}
+
+/**
+ * Create a {@link StateStore} backed by an `@xstate/store` atom.
+ *
+ * @example
+ * ```ts
+ * import { createAtom } from "@xstate/store";
+ * import { xstateStoreStateStore } from "@json-render/xstate-store";
+ *
+ * const uiAtom = createAtom<Record<string, unknown>>({ count: 0 });
+ *
+ * const store = xstateStoreStateStore({ atom: uiAtom });
+ *
+ * <StateProvider store={store}>...</StateProvider>
+ * ```
+ */
+export function xstateStoreStateStore(
+  options: XstateStoreStateStoreOptions,
+): StateStore {
+  const { atom } = options;
+
+  return createStoreAdapter({
+    getSnapshot: () => atom.get(),
+    setSnapshot: (next) => atom.set(next),
+    subscribe(listener) {
+      const sub = atom.subscribe(() => {
+        listener();
+      });
+      return () => sub.unsubscribe();
+    },
+  });
+}

packages/xstate-store/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "extends": "@internal/typescript-config/base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": "src"
+  },
+  "include": ["src"],
+  "exclude": ["node_modules", "dist"]
+}

packages/xstate-store/tsup.config.ts

@@ -0,0 +1,14 @@
+import { defineConfig } from "tsup";
+
+export default defineConfig({
+  entry: ["src/index.ts"],
+  format: ["cjs", "esm"],
+  dts: true,
+  sourcemap: true,
+  clean: true,
+  external: [
+    "@json-render/core",
+    "@json-render/core/store-utils",
+    "@xstate/store",
+  ],
+});

vitest.config.ts

@@ -3,11 +3,12 @@ import path from "path";
 
 export default defineConfig({
   resolve: {
-    // Deduplicate React so tests don't get two copies
-    // (pnpm strict resolution can cause packages/react to resolve a different copy)
+    // Deduplicate React and Vue so tests don't get two copies
+    // (pnpm strict resolution can cause packages to resolve different copies)
     alias: {
       react: path.resolve(__dirname, "node_modules/react"),
       "react-dom": path.resolve(__dirname, "node_modules/react-dom"),
+      vue: path.resolve(__dirname, "packages/vue/node_modules/vue"),
     },
   },
   test: {