vue improvements (#163)

* vue improvements

* fixes

* fixes

* fixes

* fix ci

* fix ci

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/CHANGELOG.md

@@ -1,5 +1,14 @@
 # web
 
+## 0.1.2
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react@0.9.1
+  - @json-render/core@0.9.1
+  - @json-render/codegen@0.9.1
+
 ## 0.1.1
 
 ### Patch Changes

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/changelog/page.mdx

@@ -5,6 +5,16 @@ export const metadata = pageMetadata("docs/changelog")
 
 Notable changes and updates to json-render.
 
+## v0.9.1
+
+February 2026
+
+### Fixed: Install failure due to private dependency
+
+`@json-render/react`, `@json-render/react-pdf`, and `@json-render/react-native` v0.9.0 failed to install because `@internal/react-state` (a private workspace package) was published as a dependency. The internal package is now bundled into each renderer at build time, so it no longer needs to be resolved from npm.
+
+---
+
 ## v0.9.0
 
 February 2026

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
+- `minLength` — Minimum string length (args: `{ "min": N }`)
-- `maxLength` — Maximum string length
+- `maxLength` — Maximum string length (args: `{ "max": N }`)
-- `pattern` — Match a regex pattern
+- `pattern` — Match a regex pattern (args: `{ "pattern": "regex" }`)
-- `min` — Minimum numeric value
+- `min` — Minimum numeric value (args: `{ "min": N }`)
-- `max` — Maximum numeric value
+- `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",

apps/web/package.json

@@ -1,6 +1,6 @@
 {
   "name": "web",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "type": "module",
   "private": true,
   "license": "Apache-2.0",

examples/chat/CHANGELOG.md

@@ -1,5 +1,14 @@
 # example-chat
 
+## 0.1.2
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react@0.9.1
+  - @json-render/shadcn@0.9.1
+  - @json-render/core@0.9.1
+
 ## 0.1.1
 
 ### Patch Changes

examples/chat/package.json

@@ -1,6 +1,6 @@
 {
   "name": "example-chat",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "type": "module",
   "private": true,
   "scripts": {

examples/dashboard/CHANGELOG.md

@@ -1,5 +1,14 @@
 # example-dashboard
 
+## 0.1.2
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react@0.9.1
+  - @json-render/core@0.9.1
+  - @json-render/codegen@0.9.1
+
 ## 0.1.1
 
 ### Patch Changes

examples/dashboard/package.json

@@ -1,6 +1,6 @@
 {
   "name": "example-dashboard",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "type": "module",
   "private": true,
   "scripts": {

examples/no-ai/CHANGELOG.md

@@ -1,5 +1,14 @@
 # example-no-ai
 
+## 0.1.2
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react@0.9.1
+  - @json-render/shadcn@0.9.1
+  - @json-render/core@0.9.1
+
 ## 0.1.1
 
 ### Patch Changes

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 {
+import { JSONUIProvider, Renderer } from "@json-render/react";
-  Renderer,
-  StateProvider,
-  VisibilityProvider,
-  ActionProvider,
-  ValidationProvider,
-} 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 ?? {}}>
+    <JSONUIProvider
-      <VisibilityProvider>
+      registry={registry}
-        <ActionProvider handlers={actionHandlers}>
+      initialState={spec.state ?? {}}
-          <ValidationProvider>
+      handlers={actionHandlers}
-            <Renderer spec={spec} registry={registry} />
+      functions={computedFunctions}
-          </ValidationProvider>
+    >
-        </ActionProvider>
+      <Renderer spec={spec} registry={registry} />
-      </VisibilityProvider>
+    </JSONUIProvider>
-    </StateProvider>
   );
 }
 
 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="h-screen flex flex-col bg-muted/30">
-      <div
+      {/* Example selector */}
-        className="relative bg-background border rounded-lg shadow-sm"
+      <nav className="flex gap-1 p-3 overflow-x-auto border-b bg-background shrink-0">
-        style={{ width: 960, height: 1080 }}
+        {examples.map((ex, i) => (
-      >
+          <button
-        {confettiActive && (
+            key={ex.name}
-          <div className="absolute inset-0 flex items-center justify-center pointer-events-none">
+            onClick={() => setSelectedIndex(i)}
-            <ConfettiExplosion
+            className={`px-3 py-1.5 text-sm rounded-md whitespace-nowrap transition-colors ${
-              key={confettiKey}
+              i === selectedIndex
-              portal={false}
+                ? "bg-primary text-primary-foreground"
-              force={0.8}
+                : "hover:bg-muted"
-              duration={3500}
+            }`}
-              particleCount={400}
+          >
-              particleSize={8}
+            {ex.name}
-              colors={["#00F0FF", "#7B61FF", "#FF3DFF", "#00FF94", "#FFE14D"]}
+          </button>
-              width={1600}
+        ))}
-              height="200vh"
+      </nav>
-              zIndex={1}
+
-              onComplete={() => setConfettiActive(false)}
+      {/* 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/no-ai/package.json

@@ -1,6 +1,6 @@
 {
   "name": "example-no-ai",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "type": "module",
   "private": true,
   "scripts": {

examples/react-native/CHANGELOG.md

@@ -1,5 +1,13 @@
 # example-react-native
 
+## 0.1.2
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react-native@0.9.1
+  - @json-render/core@0.9.1
+
 ## 0.1.1
 
 ### Patch Changes

examples/react-native/package.json

@@ -1,6 +1,6 @@
 {
   "name": "example-react-native",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "private": true,
   "main": "expo-router/entry",
   "scripts": {

examples/react-pdf/CHANGELOG.md

@@ -1,5 +1,13 @@
 # example-react-pdf
 
+## 0.1.2
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react-pdf@0.9.1
+  - @json-render/core@0.9.1
+
 ## 0.1.1
 
 ### Patch Changes

examples/react-pdf/package.json

@@ -1,6 +1,6 @@
 {
   "name": "example-react-pdf",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "type": "module",
   "private": true,
   "scripts": {

examples/remotion/CHANGELOG.md

@@ -1,5 +1,12 @@
 # example-remotion
 
+## 0.1.2
+
+### Patch Changes
+
+- @json-render/core@0.9.1
+- @json-render/remotion@0.9.1
+
 ## 0.1.1
 
 ### Patch Changes

examples/remotion/package.json

@@ -1,6 +1,6 @@
 {
   "name": "example-remotion",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "type": "module",
   "private": true,
   "scripts": {

examples/stripe-app/drawer-app/CHANGELOG.md

@@ -1,5 +1,13 @@
 # com.example.json-render-demo
 
+## 0.0.3
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react@0.9.1
+  - @json-render/core@0.9.1
+
 ## 0.0.2
 
 ### Patch Changes

examples/stripe-app/drawer-app/package.json

@@ -1,6 +1,6 @@
 {
   "name": "com.example.json-render-demo",
-  "version": "0.0.2",
+  "version": "0.0.3",
   "description": "Test",
   "private": true,
   "license": "~~proprietary~~",

examples/stripe-app/fullpage-app/CHANGELOG.md

@@ -1,5 +1,13 @@
 # com.example.json-render-fullpage-demo
 
+## 0.0.3
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react@0.9.1
+  - @json-render/core@0.9.1
+
 ## 0.0.2
 
 ### Patch Changes

examples/stripe-app/fullpage-app/package.json

@@ -1,6 +1,6 @@
 {
   "name": "com.example.json-render-fullpage-demo",
-  "version": "0.0.2",
+  "version": "0.0.3",
   "description": "Full-page Stripe App example (alpha)",
   "private": true,
   "license": "~~proprietary~~",

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/codegen/CHANGELOG.md

@@ -1,5 +1,11 @@
 # @json-render/codegen
 
+## 0.9.1
+
+### Patch Changes
+
+- @json-render/core@0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/codegen/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/codegen",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "Utilities for generating code from json-render UI trees",
   "keywords": [

packages/core/CHANGELOG.md

@@ -1,5 +1,7 @@
 # @json-render/core
 
+## 0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/core/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/core",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "JSON becomes real things. Define your catalog, register your components, let AI generate.",
   "keywords": [

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/jotai/CHANGELOG.md

@@ -1,5 +1,11 @@
 # @json-render/jotai
 
+## 0.9.1
+
+### Patch Changes
+
+- @json-render/core@0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/jotai/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/jotai",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "Jotai adapter for json-render StateStore",
   "keywords": [

packages/react-native/CHANGELOG.md

@@ -1,5 +1,12 @@
 # @json-render/react-native
 
+## 0.9.1
+
+### Patch Changes
+
+- b103676: Fix install failure caused by `@internal/react-state` (a private workspace package) being listed as a published dependency. The internal package is now bundled into each renderer's output at build time, so consumers no longer need to resolve it from npm.
+  - @json-render/core@0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/react-native/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/react-native",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "React Native renderer for @json-render/core. JSON becomes React Native components.",
   "keywords": [
@@ -56,10 +56,10 @@
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
-    "@json-render/core": "workspace:*",
+    "@json-render/core": "workspace:*"
-    "@internal/react-state": "workspace:*"
   },
   "devDependencies": {
+    "@internal/react-state": "workspace:*",
     "@internal/typescript-config": "workspace:*",
     "@types/react": "19.2.3",
     "react-native": "0.83.1",

packages/react-native/tsup.config.ts

@@ -3,8 +3,9 @@ import { defineConfig } from "tsup";
 export default defineConfig({
   entry: ["src/index.ts", "src/schema.ts", "src/catalog.ts"],
   format: ["cjs", "esm"],
-  dts: true,
+  dts: { resolve: ["@internal/react-state"] },
   sourcemap: true,
   clean: true,
+  noExternal: ["@internal/react-state"],
   external: ["react", "react-native", "@json-render/core", "zod"],
 });

packages/react-pdf/CHANGELOG.md

@@ -1,5 +1,12 @@
 # @json-render/react-pdf
 
+## 0.9.1
+
+### Patch Changes
+
+- b103676: Fix install failure caused by `@internal/react-state` (a private workspace package) being listed as a published dependency. The internal package is now bundled into each renderer's output at build time, so consumers no longer need to resolve it from npm.
+  - @json-render/core@0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/react-pdf/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/react-pdf",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "React PDF renderer for @json-render/core. JSON becomes PDF documents.",
   "keywords": [
@@ -61,10 +61,10 @@
   },
   "dependencies": {
     "@json-render/core": "workspace:*",
-    "@internal/react-state": "workspace:*",
     "@react-pdf/renderer": "^4.3.2"
   },
   "devDependencies": {
+    "@internal/react-state": "workspace:*",
     "@internal/typescript-config": "workspace:*",
     "@types/react": "19.2.3",
     "tsup": "^8.0.2",

packages/react-pdf/tsup.config.ts

@@ -3,8 +3,9 @@ import { defineConfig } from "tsup";
 export default defineConfig({
   entry: ["src/index.ts", "src/server.ts", "src/catalog.ts", "src/render.tsx"],
   format: ["cjs", "esm"],
-  dts: true,
+  dts: { resolve: ["@internal/react-state"] },
   sourcemap: true,
   clean: true,
+  noExternal: ["@internal/react-state"],
   external: ["react", "@json-render/core", "@react-pdf/renderer", "zod"],
 });

packages/react-state/CHANGELOG.md

@@ -1,5 +1,11 @@
 # @internal/react-state
 
+## 0.8.2
+
+### Patch Changes
+
+- @json-render/core@0.9.1
+
 ## 0.8.1
 
 ### Patch Changes

packages/react-state/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@internal/react-state",
-  "version": "0.8.1",
+  "version": "0.8.2",
   "private": true,
   "license": "Apache-2.0",
   "description": "Shared React state context for json-render renderer packages",

packages/react/CHANGELOG.md

@@ -1,5 +1,12 @@
 # @json-render/react
 
+## 0.9.1
+
+### Patch Changes
+
+- b103676: Fix install failure caused by `@internal/react-state` (a private workspace package) being listed as a published dependency. The internal package is now bundled into each renderer's output at build time, so consumers no longer need to resolve it from npm.
+  - @json-render/core@0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/react/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/react",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "React renderer for @json-render/core. JSON becomes React components.",
   "keywords": [
@@ -50,10 +50,10 @@
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
-    "@json-render/core": "workspace:*",
+    "@json-render/core": "workspace:*"
-    "@internal/react-state": "workspace:*"
   },
   "devDependencies": {
+    "@internal/react-state": "workspace:*",
     "@internal/typescript-config": "workspace:*",
     "@types/react": "19.2.3",
     "tsup": "^8.0.2",

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();
+  const { state, getSnapshot } = 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 [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
+      // Read from the store directly so validation sees values written in the
-      const currentState = stateRef.current;
+      // 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) => ({
+      const newFieldState: FieldValidationState = {
-        ...prev,
+        touched: fieldStatesRef.current[path]?.touched ?? true,
-        [path]: {
+        validated: true,
-          touched: prev[path]?.touched ?? true,
+        result,
-          validated: true,
+      };
-          result,
+      fieldStatesRef.current = {
-        },
+        ...fieldStatesRef.current,
-      }));
+        [path]: newFieldState,
+      };
+      setFieldStates(fieldStatesRef.current);
 
       return result;
     },
-    [customFunctions],
+    [customFunctions, getSnapshot],
   );
 
   const touch = useCallback((path: string) => {
-    setFieldStates((prev) => ({
+    fieldStatesRef.current = {
-      ...prev,
+      ...fieldStatesRef.current,
       [path]: {
-        ...prev[path],
+        ...fieldStatesRef.current[path],
         touched: true,
-        validated: prev[path]?.validated ?? false,
+        validated: fieldStatesRef.current[path]?.validated ?? false,
-        result: prev[path]?.result ?? null,
+        result: fieldStatesRef.current[path]?.result ?? null,
       },
-    }));
+    };
+    setFieldStates(fieldStatesRef.current);
   }, []);
 
   const clear = useCallback((path: string) => {
-    setFieldStates((prev) => {
+    const { [path]: _, ...rest } = fieldStatesRef.current;
-      const { [path]: _, ...rest } = prev;
+    fieldStatesRef.current = rest;
-      return 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)
+  // Build context with repeat scope and $computed functions
-  const fullCtx: PropResolutionContext = useMemo(
+  const fullCtx: PropResolutionContext = useMemo(() => {
-    () =>
+    const base: PropResolutionContext = repeatScope
-      repeatScope
+      ? {
-        ? {
+          ...ctx,
-            ...ctx,
+          repeatItem: repeatScope.item,
-            repeatItem: repeatScope.item,
+          repeatIndex: repeatScope.index,
-            repeatIndex: repeatScope.index,
+          repeatBasePath: repeatScope.basePath,
-            repeatBasePath: repeatScope.basePath,
+        }
-          }
+      : { ...ctx };
-        : ctx,
+    base.functions = functions;
-    [ctx, repeatScope],
+    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 `$computed` expressions in props */
+  functions?: Record<string, ComputedFunction>;
   /** Callback when state changes (uncontrolled mode) */
   onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
   children: ReactNode;
@@ -434,6 +532,7 @@ export function JSONUIProvider({
   handlers,
   navigate,
   validationFunctions,
+  functions,
   onStateChange,
   children,
 }: JSONUIProviderProps) {
@@ -444,12 +543,14 @@ export function JSONUIProvider({
       onStateChange={onStateChange}
     >
       <VisibilityProvider>
-        <ActionProvider handlers={handlers} navigate={navigate}>
+        <ValidationProvider customFunctions={validationFunctions}>
-          <ValidationProvider customFunctions={validationFunctions}>
+          <ActionProvider handlers={handlers} navigate={navigate}>
-            {children}
+            <FunctionsContext.Provider value={functions ?? EMPTY_FUNCTIONS}>
-            <ConfirmationDialogManager />
+              {children}
-          </ValidationProvider>
+              <ConfirmationDialogManager />
-        </ActionProvider>
+            </FunctionsContext.Provider>
+          </ActionProvider>
+        </ValidationProvider>
       </VisibilityProvider>
     </StateProvider>
   );
@@ -650,6 +751,8 @@ export interface CreateRendererProps {
   onAction?: (actionName: string, params?: Record<string, unknown>) => void;
   /** Callback when state changes (uncontrolled mode) */
   onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
+  /** Named functions for `$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>
-            <ValidationProvider>
+            <ActionProvider handlers={actionHandlers}>
-              <Renderer
+              <FunctionsContext.Provider value={functions ?? EMPTY_FUNCTIONS}>
-                spec={spec}
+                <Renderer
-                registry={registry}
+                  spec={spec}
-                loading={loading}
+                  registry={registry}
-                fallback={fallback}
+                  loading={loading}
-              />
+                  fallback={fallback}
-              <ConfirmationDialogManager />
+                />
-            </ValidationProvider>
+                <ConfirmationDialogManager />
-          </ActionProvider>
+              </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/react/tsup.config.ts

@@ -3,8 +3,9 @@ import { defineConfig } from "tsup";
 export default defineConfig({
   entry: ["src/index.ts", "src/schema.ts"],
   format: ["cjs", "esm"],
-  dts: true,
+  dts: { resolve: ["@internal/react-state"] },
   sourcemap: true,
   clean: true,
+  noExternal: ["@internal/react-state"],
   external: ["react", "react-dom", "@json-render/core"],
 });

packages/redux/CHANGELOG.md

@@ -1,5 +1,11 @@
 # @json-render/redux
 
+## 0.9.1
+
+### Patch Changes
+
+- @json-render/core@0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/redux/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/redux",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "Redux adapter for json-render StateStore",
   "keywords": [

packages/remotion/CHANGELOG.md

@@ -1,5 +1,11 @@
 # @json-render/remotion
 
+## 0.9.1
+
+### Patch Changes
+
+- @json-render/core@0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/remotion/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/remotion",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "Remotion renderer for @json-render/core. JSON becomes video compositions.",
   "keywords": [

packages/shadcn/CHANGELOG.md

@@ -1,5 +1,13 @@
 # @json-render/shadcn
 
+## 0.9.1
+
+### Patch Changes
+
+- Updated dependencies [b103676]
+  - @json-render/react@0.9.1
+  - @json-render/core@0.9.1
+
 ## 0.9.0
 
 ### Minor Changes

packages/shadcn/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@json-render/shadcn",
-  "version": "0.9.0",
+  "version": "0.9.1",
   "license": "Apache-2.0",
   "description": "shadcn/ui component library for @json-render/core. JSON becomes beautiful Tailwind-styled React components.",
   "keywords": [

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
+      checks: validationCheckSchema,
-        .array(
+      validateOn: validateOnSchema,
-          z.object({
-            type: z.string(),
-            message: z.string(),
-            args: z.record(z.string(), z.unknown()).optional(),
-          }),
-        )
-        .nullable(),
     }),
     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
+      checks: validationCheckSchema,
-        .array(
+      validateOn: validateOnSchema,
-          z.object({
-            type: z.string(),
-            message: z.string(),
-            args: z.record(z.string(), z.unknown()).optional(),
-          }),
-        )
-        .nullable(),
     }),
     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
+      checks: validationCheckSchema,
-        .array(
+      validateOn: validateOnSchema,
-          z.object({
-            type: z.string(),
-            message: z.string(),
-            args: z.record(z.string(), z.unknown()).optional(),
-          }),
-        )
-        .nullable(),
     }),
     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: {