fix(tanstack-start): preserve encoded percent params

- Preserve encoded percent signs through pathname normalization.
- Cover dynamic, splat, and static-path round trips.

.changeset/README.md

@@ -1,13 +0,0 @@
-# Changesets
-
-Hello and welcome! This folder has been automatically generated by `@changesets/cli`, a build tool that works
-with multi-package repos, or single-package repos to help you version and publish your code. You can
-find the full documentation for it [in the repository](https://github.com/changesets/changesets).
-
-## Adding a changeset
-
-To add a changeset, run `pnpm changeset` in the root of the repository. This will prompt you to select
-which packages have changed and what type of version bump (major, minor, or patch) should be applied.
-
-All `@json-render/*` packages are versioned together -- a changeset for any one of them will bump all
-packages to the same version.

.changeset/config.json

@@ -1,37 +0,0 @@
-{
-  "$schema": "https://unpkg.com/@changesets/config@3.1.1/schema.json",
-  "changelog": "@changesets/cli/changelog",
-  "commit": false,
-  "fixed": [
-    [
-      "@json-render/core",
-      "@json-render/react",
-      "@json-render/react-email",
-      "@json-render/react-pdf",
-      "@json-render/shadcn",
-      "@json-render/react-native",
-      "@json-render/remotion",
-      "@json-render/codegen",
-      "@json-render/zustand",
-      "@json-render/redux",
-      "@json-render/jotai",
-      "@json-render/vue",
-      "@json-render/xstate",
-      "@json-render/image",
-      "@json-render/mcp",
-      "@json-render/svelte",
-      "@json-render/solid",
-      "@json-render/react-three-fiber",
-      "@json-render/yaml",
-      "@json-render/ink"
-    ]
-  ],
-  "linked": [],
-  "access": "public",
-  "baseBranch": "main",
-  "updateInternalDependencies": "patch",
-  "privatePackages": {
-    "version": true,
-    "tag": false
-  }
-}

.github/workflows/ci.yml

@@ -13,6 +13,18 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  version-sync:
+    name: Version Sync Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: .node-version
+      - name: Check version sync
+        run: node scripts/check-version-sync.js
+
   lint:
     name: Lint
     runs-on: ubuntu-latest
@@ -21,7 +33,7 @@ jobs:
       - uses: pnpm/action-setup@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 20
+          node-version-file: .node-version
           cache: pnpm
       - run: pnpm install --frozen-lockfile
       - run: pnpm lint
@@ -34,7 +46,7 @@ jobs:
       - uses: pnpm/action-setup@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 20
+          node-version-file: .node-version
           cache: pnpm
       - run: pnpm install --frozen-lockfile
       - name: Build packages
@@ -49,7 +61,7 @@ jobs:
       - uses: pnpm/action-setup@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 20
+          node-version-file: .node-version
           cache: pnpm
       - run: pnpm install --frozen-lockfile
       - run: pnpm type-check

.github/workflows/release.yml

@@ -6,21 +6,74 @@ on:
       - main
   workflow_dispatch:
 
-concurrency: ${{ github.workflow }}-${{ github.ref }}
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: false
 
 permissions:
-  contents: write
-  pull-requests: write
+  contents: read
 
 jobs:
-  release:
-    name: Release
+  check-release:
+    name: Check for new version
     runs-on: ubuntu-latest
+    timeout-minutes: 5
+    outputs:
+      should_release: ${{ steps.check.outputs.should_release }}
+      needs_github_release: ${{ steps.check.outputs.needs_github_release }}
+      version: ${{ steps.check.outputs.version }}
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
         with:
-          fetch-depth: 0
+          node-version-file: .node-version
+
+      - name: Compare package.json version to npm and check GitHub release
+        id: check
+        run: |
+          LOCAL_VERSION=$(node -p "require('./packages/core/package.json').version")
+          echo "Local version: $LOCAL_VERSION"
+
+          NPM_VERSION=$(npm view @json-render/core version 2>/dev/null || echo "0.0.0")
+          echo "npm version: $NPM_VERSION"
+
+          if [ "$LOCAL_VERSION" != "$NPM_VERSION" ]; then
+            echo "Version changed: $NPM_VERSION -> $LOCAL_VERSION"
+            echo "should_release=true" >> "$GITHUB_OUTPUT"
+            echo "needs_github_release=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "Version unchanged on npm, skipping build and publish"
+            echo "should_release=false" >> "$GITHUB_OUTPUT"
+
+            TAG="v$LOCAL_VERSION"
+            if gh release view "$TAG" &>/dev/null; then
+              echo "GitHub release $TAG exists"
+              echo "needs_github_release=false" >> "$GITHUB_OUTPUT"
+            else
+              echo "GitHub release $TAG is missing, will create it"
+              echo "needs_github_release=true" >> "$GITHUB_OUTPUT"
+            fi
+          fi
+          echo "version=$LOCAL_VERSION" >> "$GITHUB_OUTPUT"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  publish:
+    name: Publish to npm
+    needs: check-release
+    if: needs.check-release.outputs.should_release == 'true'
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    environment: Release
+    permissions:
+      contents: read
+      id-token: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
 
       - name: Install pnpm
         uses: pnpm/action-setup@v4
@@ -28,20 +81,86 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: 20
+          node-version-file: .node-version
           cache: pnpm
           registry-url: "https://registry.npmjs.org"
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
 
-      - name: Create Release Pull Request or Publish
-        uses: changesets/action@v1
-        with:
-          version: pnpm ci:version
-          publish: pnpm ci:publish
-          title: "chore: version packages"
-          commit: "chore: version packages"
+      - name: Build packages
+        run: pnpm run build
+
+      - name: Publish all public packages
+        run: |
+          LOCAL_VERSION="${{ needs.check-release.outputs.version }}"
+          FAILED=""
+
+          publish_pkg() {
+            local dir="$1" name="$2"
+            REGISTRY_VERSION=$(npm view "$name" version 2>/dev/null || echo "0.0.0")
+            if [ "$LOCAL_VERSION" = "$REGISTRY_VERSION" ]; then
+              echo "$name@$LOCAL_VERSION already published, skipping"
+              return 0
+            fi
+            echo "Publishing $name@$LOCAL_VERSION..."
+            TARBALL=$(cd "$dir" && pnpm pack --pack-destination /tmp | tail -1)
+            if ! npm publish "$TARBALL" --provenance --access public; then
+              FAILED="$FAILED $name"
+            fi
+          }
+
+          for dir in packages/*/; do
+            PKG_NAME=$(node -p "try { const p = require('./$dir/package.json'); p.private ? '' : p.name } catch { '' }")
+            [ -z "$PKG_NAME" ] && continue
+            publish_pkg "$dir" "$PKG_NAME"
+          done
+
+          if [ -n "$FAILED" ]; then
+            echo "Failed to publish:$FAILED"
+            exit 1
+          fi
+
+  github-release:
+    name: Create GitHub Release
+    needs: [check-release, publish]
+    if: >-
+      always()
+      && needs.check-release.outputs.needs_github_release == 'true'
+      && (needs.publish.result == 'success' || needs.publish.result == 'skipped')
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Extract changelog entry
+        run: |
+          VERSION="${{ needs.check-release.outputs.version }}"
+          awk '/<!-- release:start -->/{found=1; next} /<!-- release:end -->/{found=0} found{print}' CHANGELOG.md > /tmp/release-notes.md
+
+          LINES=$(wc -l < /tmp/release-notes.md | tr -d ' ')
+          if [ "$LINES" -lt 2 ]; then
+            echo "Error: No release notes found between <!-- release:start --> and <!-- release:end --> markers in CHANGELOG.md"
+            exit 1
+          fi
+          echo "Extracted release notes for $VERSION ($LINES lines)"
+
+      - name: Create GitHub Release
+        run: |
+          VERSION="${{ needs.check-release.outputs.version }}"
+          TAG="v$VERSION"
+
+          if gh release view "$TAG" &>/dev/null; then
+            echo "Release $TAG already exists"
+          else
+            echo "Creating release $TAG..."
+            gh release create "$TAG" \
+              --title "$TAG" \
+              --target ${{ github.sha }} \
+              --notes-file /tmp/release-notes.md
+          fi
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          NODE_AUTH_TOKEN: ${{ secrets.NPM_VERCEL_TOKEN_ELEVATED }}

.gitignore

@@ -29,6 +29,8 @@ build
 dist
 *.tsbuildinfo
 .svelte-kit/
+tsup.config.bundled_*.mjs
+next-env.d.ts
 
 
 # Debug

.node-version

@@ -0,0 +1 @@
+24

AGENTS.md

@@ -73,25 +73,20 @@ Do **not** add `--port` flags -- portless handles port assignment automatically.
   - Skills in `skills/*/SKILL.md` (if the package has a corresponding skill)
   - `AGENTS.md` (if workflow or conventions change)
 
-## Releases
+## Releasing
 
-This monorepo uses [Changesets](https://github.com/changesets/changesets) for versioning and publishing.
+Releases are manual, single-PR affairs. The maintainer controls the changelog voice and format.
 
-### Fixed version group
-
-All public `@json-render/*` packages are in a **fixed** group (see `.changeset/config.json`). A changeset that bumps any one of them bumps all of them to the same version. You only need to list the packages that actually changed in the changeset front matter — the fixed group handles the rest.
+All public `@json-render/*` packages share the same version. The canonical version lives in `packages/core/package.json`.
 
 ### Preparing a release
 
-When asked to prepare a release (e.g. "prepare v0.12.0"):
+When asked to prepare a release (e.g. "prepare v0.17.0"):
 
-1. **Create a changeset file** at `.changeset/v0-<N>-release.md` following the existing pattern:
-   - YAML front matter listing changed packages with bump type (`minor` for feature releases, `patch` for bug-fix-only releases)
-   - A one-line summary, then `### New:` / `### Improved:` / `### Fixed:` sections describing each change
-   - Always list `@json-render/core` plus any packages with actual code changes
-2. **Do NOT bump versions** in `package.json` files — CI runs `pnpm ci:version` (which calls `changeset version`) to do that automatically
-3. **Do NOT manually write `CHANGELOG.md`** entries — `changeset version` generates them from the changeset file
-4. **Add new packages to the fixed group** in `.changeset/config.json` if they should be versioned together with the rest
+1. Create a branch (e.g. `prepare-v0.17.0`)
+2. Bump the version in `packages/core/package.json`
+3. Run `pnpm run version:sync` to update all other `@json-render/*` packages
+4. Write the changelog entry in `CHANGELOG.md`, wrapped in `<!-- release:start -->` and `<!-- release:end -->` markers (move the markers from the previous entry to the new one)
 5. **Fill documentation gaps** — every public package should have:
    - A row in the root `README.md` packages table
    - A renderer section in the root `README.md` (if it's a renderer)
@@ -101,12 +96,15 @@ When asked to prepare a release (e.g. "prepare v0.12.0"):
    - A skill at `skills/<name>/SKILL.md`
    - A `packages/<name>/README.md`
 6. **Run `pnpm type-check`** after all changes to verify nothing is broken
+7. Open a PR and merge to `main`
 
-### CI scripts
+CI compares the `@json-render/core` version to what's on npm. If it differs, it builds, publishes all public packages, and creates the GitHub release automatically. The release body is extracted from the content between the markers.
 
-- `pnpm changeset` — interactively create a new changeset
-- `pnpm ci:version` — run `changeset version` + lockfile update (CI only)
-- `pnpm ci:publish` — build all packages and publish to npm (CI only)
+### Scripts
+
+- `pnpm run version:sync` — sync all `@json-render/*` package versions to match `@json-render/core`
+- `pnpm run version:check` — verify all versions are in sync (runs in CI)
+- `pnpm run ci:publish` — build all packages and publish to npm (CI only)
 
 <!-- opensrc:start -->
 

CHANGELOG.md

@@ -0,0 +1,92 @@
+# Changelog
+
+## 0.20.0
+
+<!-- release:start -->
+
+### New Features
+
+- **Named slots for React:** Components can declare named slots such as `header` and `footer`, while `children` remains the default slot. Slots are preserved through validation, streaming, nested conversion, code export, playground views, and Devtools navigation (#320). Built from the original contribution by @wotnak in #105
+- **Nested repeats:** `repeat.statePath` now accepts item-relative paths such as `{ "$item": "employees" }`, enabling nested data rendering across React, React Native, React Email, React PDF, Image, Ink, Solid, Svelte, and Vue (#319). Built from the original contribution by @tmchow in #256
+- **Harness chat example:** Added a complete Next.js example using the AI SDK 7 harness adapter, agent delegation, sandbox transport, and json-render components (#302)
+
+### Bug Fixes
+
+- **Chained action params:** Named `onSuccess` and `onError` actions now receive their configured `params` across core and all renderer bridges (#307)
+- **Consistent optional visibility:** Element `visible` fields now remain optional across Zod 4 versions, while prompts explicitly require `children` arrays for every element (#299)
+- **Spec validation and autofix:** Dangling child references are pruned, malformed visibility conditions are reported, and repeated items can be filtered safely (#300)
+
+### Improvements
+
+- **Release toolchain hardening:** The workspace now requires Node.js 24 and pnpm 11, enforces package engine checks, and applies a minimum package release age (#293)
+
+### Breaking Changes
+
+- Custom renderer bridges that implement the core `executeAction` callback must now accept an `ActionBinding` instead of a bare action name. This exposes chained action params to custom integrations at compile time (#307)
+
+### Contributors
+
+- @ctate
+- @Railly
+- @tmchow
+- @wotnak
+<!-- release:end -->
+
+## 0.19.0
+
+### New Features
+
+- **Custom directives API** — `@json-render/core` now supports custom directives via `defineDirective`, letting you declare new JSON shapes (like `$format`, `$math`) that resolve to computed values at render time. Directives compose naturally — nest `$format` over `$math` over `$state` and they resolve inside-out. All four renderers (React, Vue, Svelte, Solid) have built-in directive resolution (#279)
+- **`@json-render/directives`** — New package shipping seven ready-made directives: `$format` (date, currency, number, percent via `Intl`), `$math` (add, subtract, multiply, divide, mod, min, max, round, floor, ceil, abs), `$concat`, `$count`, `$truncate`, `$pluralize`, and `$join`. Also exports `createI18nDirective` for `$t` translation keys with `{{param}}` interpolation, and `standardDirectives` for one-line registration (#279)
+
+### Improvements
+
+- **Example READMEs** — Added documentation to the chat, dashboard, game-engine, and no-ai examples (#277)
+
+### Contributors
+
+- @ctate
+
+## 0.18.0
+
+### New Features
+
+- **Devtools** — Five new packages for inspecting json-render apps in the browser: `@json-render/devtools` (framework-agnostic core), plus `@json-render/devtools-react`, `@json-render/devtools-vue`, `@json-render/devtools-svelte`, and `@json-render/devtools-solid` adapters. Drop `<JsonRenderDevtools />` into your app to get a shadow-DOM-isolated panel with six tabs (Spec, State, Actions, Stream, Catalog, Pick), a DOM picker that maps clicked elements back to spec keys via `data-jr-key`, a capped event store, and server-side stream tap utilities. Floating toggle or `Cmd`/`Ctrl` + `Shift` + `J`, tree-shakes to `null` in production (#273)
+- **Devtools example** — New `examples/devtools` Next.js demo showing the full devtools panel wired up to an AI chat endpoint and a component catalog (#273)
+- **Action observer and devtools flag in core** — `@json-render/core` now exposes an action observer and a devtools enablement flag that adapters use to mirror actions and stream events into the panel (#273)
+
+### Bug Fixes
+
+- **Zod 4 schema formatting** — `formatZodType` now correctly handles `z.record()`, `z.default()`, and `z.literal()` types from Zod 4, which previously produced incorrect or empty output in generated prompts and schemas (#239)
+
+### Improvements
+
+- **Zod 4 test coverage** — Added unit tests for `formatZodType` covering record, default, and literal types to guard against regressions (#272)
+
+### Contributors
+
+- @ctate
+- @mvanhorn
+
+## 0.17.0
+
+### New Features
+
+- **Gaussian Splatting** — Added `GaussianSplat` component to `@json-render/react-three-fiber`, bringing the component count to 20. Composable with all existing R3F components (lights, controls, post-processing) via drei's Splat loader (#259)
+- **Standalone gsplat example** — Experimental demo app showcasing Gaussian Splatting with gsplat.js (no Three.js dependency), featuring scene selector, live JSON spec viewer, and progress indicator (#259)
+- **R3F gsplat example** — Demo app with five scenes: splat showroom, splat with primitives, multi-splat, post-processing effects, and animated floating splat (#259)
+
+### Improved
+
+- **AI output quality** — Improved prompt output and schema generation for more reliable AI-generated specs (#268)
+
+### Contributors
+
+- @ctate
+- @willmanzoli
+
+## 0.16.0
+
+### Improved
+
+- **Release process** — Switched from Changesets to a manual single-PR release workflow with changelog markers and automatic npm publish on version bump

README.md

@@ -25,7 +25,9 @@ npm install @json-render/core @json-render/svelte
 npm install @json-render/core @json-render/solid
 # or for terminal UIs
 npm install @json-render/core @json-render/ink ink react
-# or for 3D scenes
+# or for full Next.js apps (routes, layouts, SSR, metadata)
+npm install @json-render/core @json-render/react @json-render/next
+# or for 3D scenes (and gaussian splatting via the GaussianSplat component)
 npm install @json-render/core @json-render/react-three-fiber @react-three/fiber @react-three/drei three
 ```
 
@@ -125,14 +127,23 @@ function Dashboard({ spec }) {
 | `@json-render/svelte`       | Svelte 5 renderer with runes-based reactivity                          |
 | `@json-render/solid`        | SolidJS renderer with fine-grained reactive contexts                   |
 | `@json-render/shadcn`       | 36 pre-built shadcn/ui components (Radix UI + Tailwind CSS)            |
-| `@json-render/react-three-fiber` | React Three Fiber renderer for 3D scenes (19 built-in components)  |
+| `@json-render/shadcn-svelte`| 36 pre-built shadcn-svelte components (Svelte 5 + Tailwind CSS)        |
+| `@json-render/react-three-fiber` | React Three Fiber renderer for 3D scenes (20 built-in components, including GaussianSplat)  |
 | `@json-render/react-native` | React Native renderer with standard mobile components                  |
+| `@json-render/next`         | Next.js renderer — JSON becomes full apps with routes, layouts, SSR    |
+| `@json-render/tanstack-start` | TanStack Start renderer — full apps with routes, layouts, SSR, and head metadata |
 | `@json-render/remotion`     | Remotion video renderer, timeline schema                               |
 | `@json-render/react-pdf`    | React PDF renderer for generating PDF documents from specs             |
 | `@json-render/react-email`  | React Email renderer for HTML/plain-text emails from specs             |
 | `@json-render/ink`          | Ink terminal renderer with built-in components for interactive TUIs.   |
 | `@json-render/image`        | Image renderer for SVG/PNG output (OG images, social cards) via Satori |
+| `@json-render/directives`   | Pre-built custom directives — $format, $math, $concat, $count, $truncate, $pluralize, $join, $t (i18n) |
 | `@json-render/codegen`      | Utilities for generating code from json-render UI trees                |
+| `@json-render/devtools`     | Framework-agnostic devtools core — panel UI, event store, picker, stream taps |
+| `@json-render/devtools-react`   | React adapter for `@json-render/devtools` (drop-in `<JsonRenderDevtools />`)     |
+| `@json-render/devtools-vue`     | Vue adapter for `@json-render/devtools`                                           |
+| `@json-render/devtools-svelte`  | Svelte adapter for `@json-render/devtools`                                        |
+| `@json-render/devtools-solid`   | SolidJS adapter for `@json-render/devtools`                                       |
 | `@json-render/redux`        | Redux / Redux Toolkit adapter for `StateStore`                         |
 | `@json-render/zustand`      | Zustand adapter for `StateStore`                                       |
 | `@json-render/jotai`        | Jotai adapter for `StateStore`                                         |
@@ -458,6 +469,7 @@ const catalog = defineCatalog(schema, {
     Sphere: threeComponentDefinitions.Sphere,
     AmbientLight: threeComponentDefinitions.AmbientLight,
     DirectionalLight: threeComponentDefinitions.DirectionalLight,
+    GaussianSplat: threeComponentDefinitions.GaussianSplat,
     OrbitControls: threeComponentDefinitions.OrbitControls,
   },
   actions: {},
@@ -469,6 +481,7 @@ const { registry } = defineRegistry(catalog, {
     Sphere: threeComponents.Sphere,
     AmbientLight: threeComponents.AmbientLight,
     DirectionalLight: threeComponents.DirectionalLight,
+    GaussianSplat: threeComponents.GaussianSplat,
     OrbitControls: threeComponents.OrbitControls,
   },
 });
@@ -482,6 +495,146 @@ const { registry } = defineRegistry(catalog, {
 />;
 ```
 
+### Next.js (Full Apps)
+
+```typescript
+import type { NextAppSpec } from "@json-render/next";
+import { createNextApp } from "@json-render/next/server";
+import { NextAppProvider } from "@json-render/next";
+
+const spec: NextAppSpec = {
+  metadata: { title: { default: "My App", template: "%s | My App" } },
+  layouts: {
+    main: {
+      root: "shell",
+      elements: {
+        shell: { type: "Container", props: {}, children: ["nav", "slot"] },
+        nav: { type: "NavBar", props: {}, children: [] },
+        slot: { type: "Slot", props: {}, children: [] },
+      },
+    },
+  },
+  routes: {
+    "/": {
+      layout: "main",
+      metadata: { title: "Home" },
+      page: {
+        root: "hero",
+        elements: {
+          hero: { type: "Card", props: { title: "Welcome" }, children: [] },
+        },
+      },
+    },
+  },
+};
+
+// Server: creates Page, generateMetadata, generateStaticParams
+const app = createNextApp({ spec });
+
+// Client: wrap your layout with NextAppProvider
+// <NextAppProvider registry={registry} handlers={handlers}>
+//   {children}
+// </NextAppProvider>
+```
+
+### TanStack Start (Full Apps)
+
+```tsx
+import { createFileRoute, notFound } from "@tanstack/react-router";
+import {
+  PageRenderer,
+  StartErrorBoundary,
+  StartLoading,
+  StartNotFound,
+  type StartAppSpec,
+} from "@json-render/tanstack-start";
+import { createStartApp } from "@json-render/tanstack-start/server";
+
+const spec: StartAppSpec = {
+  metadata: { title: { default: "My App", template: "%s | My App" } },
+  routes: {
+    "/": {
+      metadata: { title: "Home" },
+      page: {
+        root: "hero",
+        elements: {
+          hero: { type: "Card", props: { title: "Welcome" }, children: [] },
+        },
+      },
+    },
+  },
+};
+
+const { getPageData, getHead } = createStartApp({ spec });
+
+export const Route = createFileRoute("/$")({
+  loader: async ({ location }) => {
+    const data = await getPageData({ pathname: location.pathname });
+    if (!data) throw notFound();
+    return data;
+  },
+  head: ({ match }) => getHead({ pathname: match.pathname }),
+  component: () => <PageRenderer {...Route.useLoaderData()} />,
+  pendingComponent: StartLoading,
+  errorComponent: StartErrorBoundary,
+  notFoundComponent: StartNotFound,
+});
+```
+
+Wrap the root route's outlet with `<StartAppProvider spec={spec}>` so route
+fallback components can resolve the current route. Pass named `$computed`
+implementations through its `functions` prop.
+
+### shadcn-svelte (Svelte)
+
+```typescript
+import { defineCatalog } from "@json-render/core";
+import { schema } from "@json-render/svelte/schema";
+import { defineRegistry, Renderer } from "@json-render/svelte";
+import { shadcnComponentDefinitions } from "@json-render/shadcn-svelte/catalog";
+import { shadcnComponents } from "@json-render/shadcn-svelte";
+
+const catalog = defineCatalog(schema, {
+  components: {
+    Card: shadcnComponentDefinitions.Card,
+    Stack: shadcnComponentDefinitions.Stack,
+    Heading: shadcnComponentDefinitions.Heading,
+    Button: shadcnComponentDefinitions.Button,
+  },
+  actions: {},
+});
+
+const { registry } = defineRegistry(catalog, {
+  components: {
+    Card: shadcnComponents.Card,
+    Stack: shadcnComponents.Stack,
+    Heading: shadcnComponents.Heading,
+    Button: shadcnComponents.Button,
+  },
+});
+
+// In your Svelte component:
+// <Renderer spec={spec} registry={registry} />
+```
+
+### Devtools
+
+Drop-in inspector panel for any json-render app. Spec tree, state editor, action log, stream log, catalog browser, DOM picker.
+
+```tsx
+// React
+import { JsonRenderDevtools } from "@json-render/devtools-react";
+
+<JSONUIProvider registry={registry} handlers={handlers}>
+  <Renderer spec={spec} registry={registry} />
+  <JsonRenderDevtools spec={spec} catalog={catalog} messages={messages} />
+</JSONUIProvider>;
+```
+
+Floating toggle appears bottom-right. Hotkey: `Ctrl`/`Cmd` + `Shift` + `J`. Tree-shakes to `null` in production.
+
+Available for React, Vue, Svelte, and Solid — swap `@json-render/devtools-react` for the adapter that matches your renderer.
+
 ### Ink (Terminal)
 
 ```tsx
@@ -652,6 +805,8 @@ pnpm dev
 - Vue Example: run `pnpm dev` in `examples/vue`
 - Vite Renderers (React + Vue + Svelte + Solid): run `pnpm dev` in `examples/vite-renderers`
 - React Native example: run `npx expo start` in `examples/react-native`
+- Gaussian Splatting (R3F): run `pnpm dev` in `examples/react-three-fiber-gsplat`
+- Gaussian Splatting (experimental standalone gsplat.js demo): run `pnpm dev` in `examples/gsplat`
 
 ## How It Works
 

apps/web/CHANGELOG.md

@@ -1,5 +1,15 @@
 # web
 
+## 0.1.11
+
+### Patch Changes
+
+- Updated dependencies [519a538]
+  - @json-render/core@0.16.0
+  - @json-render/codegen@0.16.0
+  - @json-render/react@0.16.0
+  - @json-render/yaml@0.16.0
+
 ## 0.1.10
 
 ### Patch Changes

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

@@ -339,17 +339,18 @@ setSpec({ ...applySpecPatch(spec, patch) });
 
 ### nestedToFlat
 
-Convert a nested element tree (with inline children) into the flat `Spec` format:
+Convert a nested element tree (with inline children and named slots) into the flat `Spec` format:
 
 ```typescript
 import { nestedToFlat } from '@json-render/core';
 
 const flat = nestedToFlat({
-  type: "Card",
-  props: { title: "Hello" },
-  children: [
-    { type: "Text", props: { content: "World" }, children: [] }
-  ],
+  type: "Layout",
+  props: {},
+  children: [{ type: "Text", props: { content: "Main" }, children: [] }],
+  slots: {
+    header: [{ type: "Heading", props: { text: "Header" }, children: [] }],
+  },
 });
 // { root: "el-0", elements: { "el-0": ..., "el-1": ... } }
 ```
@@ -648,9 +649,10 @@ interface UIElement {
   type: string;
   props: Record<string, unknown>;
   children?: string[];          // Keys of child elements
+  slots?: Record<string, string[]>; // Named slots mapped to child keys
   visible?: VisibilityCondition;
   on?: Record<string, ActionBinding | ActionBinding[]>;  // Event bindings
-  repeat?: { statePath: string; key?: string };           // Repeat for arrays
+  repeat?: { statePath: string | { $item: string }; key?: string }; // Repeat for arrays
 }
 ```
 
@@ -666,7 +668,7 @@ interface Spec {
 }
 ```
 
-Elements are stored as a flat map with string keys. The tree structure is built by following the `children` arrays.
+Elements are stored as a flat map with string keys. The tree structure is built by following `children` and named `slots` references.
 
 ### ActionBinding
 

apps/web/app/(main)/docs/api/devtools-react/page.mdx

@@ -0,0 +1,59 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/devtools-react")
+
+# @json-render/devtools-react
+
+React adapter for the json-render devtools. Drop-in `<JsonRenderDevtools />` component.
+
+See the [Devtools guide](/docs/devtools) for the drop-in walkthrough.
+
+## JsonRenderDevtools
+
+```tsx
+import { JsonRenderDevtools } from "@json-render/devtools-react";
+
+<JSONUIProvider registry={registry} handlers={handlers}>
+  <Renderer spec={spec} registry={registry} />
+  <JsonRenderDevtools spec={spec} catalog={catalog} messages={messages} />
+</JSONUIProvider>
+```
+
+### Props
+
+```tsx
+interface JsonRenderDevtoolsProps {
+  /** Current spec being rendered. */
+  spec?: Spec | null;
+  /** Catalog definition (required for the Catalog panel). */
+  catalog?: Catalog | null;
+  /** AI SDK useChat messages array. */
+  messages?: readonly UIMessage[];
+  /** Start the panel open. Default: false. */
+  initialOpen?: boolean;
+  /** Floating toggle position. */
+  position?: "bottom-right" | "bottom-left" | "right";
+  /** Toggle keybinding, or false to disable. Default: "mod+shift+j". */
+  hotkey?: string | false;
+  /** Ring buffer size. Default: 500. */
+  bufferSize?: number;
+  /** Fires for every devtools event. */
+  onEvent?: (evt: DevtoolsEvent) => void;
+}
+```
+
+In production builds the component renders `null`.
+
+## useJsonRenderDevtools
+
+```tsx
+import { useJsonRenderDevtools } from "@json-render/devtools-react";
+
+const devtools = useJsonRenderDevtools();
+devtools?.open();
+devtools?.toggle();
+devtools?.close();
+devtools?.clear();
+devtools?.recordEvent({ kind: "stream-text", at: Date.now(), text: "hi" });
+```
+
+Access the running devtools instance from anywhere in the React tree. Returns `null` in production or before the component has mounted.

apps/web/app/(main)/docs/api/devtools-solid/page.mdx

@@ -0,0 +1,38 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/devtools-solid")
+
+# @json-render/devtools-solid
+
+SolidJS adapter for the json-render devtools. Drop-in `<JsonRenderDevtools />` component.
+
+See the [Devtools guide](/docs/devtools) for the drop-in walkthrough.
+
+## JsonRenderDevtools
+
+```tsx
+import { JsonRenderDevtools } from "@json-render/devtools-solid";
+
+<JSONUIProvider registry={registry}>
+  <Renderer spec={spec()} registry={registry} />
+  <JsonRenderDevtools
+    spec={spec()}
+    catalog={catalog}
+    messages={messages()}
+  />
+</JSONUIProvider>
+```
+
+### Props
+
+Same shape as the React adapter:
+
+- `spec`
+- `catalog`
+- `messages`
+- `initialOpen`
+- `position`
+- `hotkey`
+- `bufferSize`
+- `onEvent`
+
+In production builds the component renders `null`.

apps/web/app/(main)/docs/api/devtools-svelte/page.mdx

@@ -0,0 +1,36 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/devtools-svelte")
+
+# @json-render/devtools-svelte
+
+Svelte adapter for the json-render devtools. Drop-in `<JsonRenderDevtools />` component.
+
+See the [Devtools guide](/docs/devtools) for the drop-in walkthrough.
+
+## JsonRenderDevtools
+
+```svelte
+<script>
+  import { JsonRenderDevtools } from "@json-render/devtools-svelte";
+</script>
+
+<JSONUIProvider {registry}>
+  <Renderer {spec} {registry} />
+  <JsonRenderDevtools {spec} {catalog} {messages} />
+</JSONUIProvider>
+```
+
+### Props
+
+Same shape as the React adapter:
+
+- `spec`
+- `catalog`
+- `messages`
+- `initialOpen`
+- `position`
+- `hotkey`
+- `bufferSize`
+- `onEvent`
+
+In production builds the component renders nothing.

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

@@ -0,0 +1,38 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/devtools-vue")
+
+# @json-render/devtools-vue
+
+Vue adapter for the json-render devtools. Drop-in `<JsonRenderDevtools />` component.
+
+See the [Devtools guide](/docs/devtools) for the drop-in walkthrough.
+
+## JsonRenderDevtools
+
+```vue
+<script setup>
+import { JsonRenderDevtools } from "@json-render/devtools-vue";
+</script>
+
+<template>
+  <JSONUIProvider :registry="registry">
+    <Renderer :spec="spec" :registry="registry" />
+    <JsonRenderDevtools :spec="spec" :catalog="catalog" :messages="messages" />
+  </JSONUIProvider>
+</template>
+```
+
+### Props
+
+Same shape as the React adapter:
+
+- `spec`
+- `catalog`
+- `messages`
+- `initialOpen`
+- `position`
+- `hotkey`
+- `bufferSize`
+- `onEvent`
+
+In production builds the component renders nothing.

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

@@ -0,0 +1,146 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/devtools")
+
+# @json-render/devtools
+
+Framework-agnostic core for the json-render devtools — vanilla TS panel UI, event store, DOM picker, and stream tap utilities. Every framework-specific adapter package depends on this.
+
+Most users never import from this package directly. Pick the adapter that matches your renderer (`@json-render/devtools-react`, `@json-render/devtools-vue`, etc.) and drop the `<JsonRenderDevtools />` component into your app.
+
+See the [Devtools guide](/docs/devtools) for the drop-in walkthrough.
+
+## Event Store
+
+### createEventStore
+
+```ts
+function createEventStore(options?: { bufferSize?: number }): EventStore
+
+interface EventStore {
+  push: (event: DevtoolsEvent) => void;
+  snapshot: () => DevtoolsEvent[];
+  subscribe: (listener: () => void) => () => void;
+  clear: () => void;
+  size: () => number;
+}
+```
+
+Ring-buffered pub/sub of `DevtoolsEvent`. Shared by every panel and every stream tap.
+
+## Panel
+
+### createPanel
+
+```ts
+function createPanel(options: PanelOptions): PanelHandle
+
+interface PanelHandle {
+  open: () => void;
+  close: () => void;
+  toggle: () => void;
+  isOpen: () => boolean;
+  refresh: () => void;
+  destroy: () => void;
+}
+```
+
+Mount the panel into a host document. Adapters call this internally.
+
+### Panel tabs
+
+Each tab is a factory function that returns a `TabDef`:
+
+```ts
+import {
+  specTab,
+  stateTab,
+  actionsTab,
+  streamTab,
+  catalogTab,
+  pickerTab,
+} from "@json-render/devtools";
+```
+
+## Stream Taps
+
+### tapJsonRenderStream
+
+```ts
+function tapJsonRenderStream(
+  stream: ReadableStream<StreamChunk>,
+  events: EventStore,
+): ReadableStream<StreamChunk>
+```
+
+Mirror the spec patches flowing through a `pipeJsonRender` transform into a devtools event store. Returns the original stream unchanged — the tap just forks a copy.
+
+### tapYamlStream
+
+```ts
+function tapYamlStream(
+  stream: ReadableStream<StreamChunk>,
+  events: EventStore,
+): ReadableStream<StreamChunk>
+```
+
+YAML equivalent of `tapJsonRenderStream`.
+
+### scanMessageParts
+
+```ts
+function scanMessageParts(
+  parts: readonly DataPart[] | undefined,
+  events: EventStore,
+  seen: WeakSet<object>,
+): void
+```
+
+Client-side helper: scan an AI SDK message's `parts` array for spec data parts and push matching events into the store. Idempotent via `seen` — call it on every render of a chat UI.
+
+## Picker
+
+### startPicker
+
+```ts
+function startPicker(options: PickerOptions): PickerSession | null
+
+interface PickerOptions {
+  onPick: (key: string) => void;
+  onCancel?: () => void;
+}
+```
+
+Start a DOM picker session. Hovering paints an outline on any element carrying `data-jr-key`; clicking fires `onPick` with the spec key. Returns `null` in environments without a DOM.
+
+### findElementByKey / highlightElement
+
+```ts
+function findElementByKey(key: string): Element | null
+function highlightElement(key: string, durationMs?: number): void
+```
+
+Look up the live DOM node for a spec element key, or briefly paint an outline around it.
+
+## Types
+
+### DevtoolsEvent
+
+```ts
+type DevtoolsEvent =
+  | { kind: "spec-changed"; at: number; spec: Spec }
+  | { kind: "state-set"; at: number; path: string; prev: unknown; next: unknown }
+  | { kind: "action-dispatched"; at: number; id: string; name: string; params?: unknown }
+  | { kind: "action-settled"; at: number; id: string; ok: boolean; result?: unknown; error?: string; durationMs: number }
+  | { kind: "stream-patch"; at: number; patch: JsonPatch; source: "json" | "yaml" }
+  | { kind: "stream-text"; at: number; text: string }
+  | { kind: "stream-usage"; at: number; usage: TokenUsage }
+  | { kind: "stream-lifecycle"; at: number; phase: "start" | "end"; ok?: boolean };
+```
+
+### isProduction
+
+```ts
+function isProduction(): boolean
+```
+
+`true` when `process.env.NODE_ENV === "production"`. Adapters use this to short-circuit to a null render.

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

@@ -0,0 +1,407 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/directives")
+
+# @json-render/directives
+
+Pre-built custom directives for `@json-render/core`. Drop them into your catalog and renderer to add formatting, math, string manipulation, and i18n.
+
+## Install
+
+```bash
+npm install @json-render/directives
+```
+
+## Quick Start
+
+```typescript
+import { standardDirectives } from '@json-render/directives';
+
+// Wire into prompt generation
+const prompt = catalog.prompt({ directives: standardDirectives });
+
+// Wire into the renderer
+<JSONUIProvider spec={spec} directives={standardDirectives}>
+  ...
+</JSONUIProvider>
+```
+
+To add factory directives like `createI18nDirective`, spread the array:
+
+```typescript
+import { standardDirectives, createI18nDirective } from '@json-render/directives';
+
+const directives = [...standardDirectives, createI18nDirective(config)];
+```
+
+## Directives
+
+### `$format` — Locale-aware value formatting
+
+Formats values using `Intl` formatters. Supports `date`, `currency`, `number`, and `percent`.
+
+```json
+{ "$format": "currency", "value": { "$state": "/cart/total" }, "currency": "USD" }
+```
+
+```json
+{ "$format": "date", "value": { "$state": "/user/createdAt" } }
+```
+
+```json
+{ "$format": "number", "value": 1234567, "notation": "compact" }
+```
+
+```json
+{ "$format": "percent", "value": 0.75 }
+```
+
+Relative dates are also supported:
+
+```json
+{ "$format": "date", "value": { "$state": "/post/createdAt" }, "style": "relative" }
+```
+
+This returns strings like `"3h ago"`, `"2d from now"`, or `"just now"`.
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>$format</code></td>
+      <td><code>{'\"date\" | \"currency\" | \"number\" | \"percent\"'}</code></td>
+      <td>Format type.</td>
+    </tr>
+    <tr>
+      <td><code>value</code></td>
+      <td><code>unknown</code></td>
+      <td>Value to format. Accepts any dynamic expression.</td>
+    </tr>
+    <tr>
+      <td><code>locale</code></td>
+      <td><code>string</code></td>
+      <td>Optional. Locale for formatting (e.g. <code>"en-US"</code>).</td>
+    </tr>
+    <tr>
+      <td><code>currency</code></td>
+      <td><code>string</code></td>
+      <td>Optional. Currency code for <code>"currency"</code> format. Default: <code>"USD"</code>.</td>
+    </tr>
+    <tr>
+      <td><code>notation</code></td>
+      <td><code>string</code></td>
+      <td>Optional. Notation for <code>"number"</code> format (e.g. <code>"compact"</code>).</td>
+    </tr>
+    <tr>
+      <td><code>style</code></td>
+      <td><code>string</code></td>
+      <td>Optional. Set to <code>"relative"</code> for relative date formatting.</td>
+    </tr>
+    <tr>
+      <td><code>options</code></td>
+      <td><code>{'Record<string, unknown>'}</code></td>
+      <td>Optional. Extra <code>Intl</code> formatter options.</td>
+    </tr>
+  </tbody>
+</table>
+
+### `$math` — Arithmetic operations
+
+Performs arithmetic on one or two operands. Operands accept any dynamic expression.
+
+```json
+{ "$math": "add", "a": { "$state": "/subtotal" }, "b": { "$state": "/tax" } }
+```
+
+```json
+{ "$math": "round", "a": 3.7 }
+```
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>$math</code></td>
+      <td><code>{'\"add\" | \"subtract\" | \"multiply\" | \"divide\" | \"mod\" | \"min\" | \"max\" | \"round\" | \"floor\" | \"ceil\" | \"abs\"'}</code></td>
+      <td>Operation to perform.</td>
+    </tr>
+    <tr>
+      <td><code>a</code></td>
+      <td><code>unknown</code></td>
+      <td>First operand. Defaults to <code>0</code> if missing.</td>
+    </tr>
+    <tr>
+      <td><code>b</code></td>
+      <td><code>unknown</code></td>
+      <td>Second operand (binary ops only). Defaults to <code>0</code> if missing.</td>
+    </tr>
+  </tbody>
+</table>
+
+Unary operations (`round`, `floor`, `ceil`, `abs`) only use `a`. Division by zero returns `0`.
+
+### `$concat` — String concatenation
+
+Concatenates multiple values into a single string. Each element is resolved then joined.
+
+```json
+{ "$concat": [{ "$state": "/user/firstName" }, " ", { "$state": "/user/lastName" }] }
+```
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>$concat</code></td>
+      <td><code>{'unknown[]'}</code></td>
+      <td>Array of values to concatenate. Each is resolved, converted to string, and joined.</td>
+    </tr>
+  </tbody>
+</table>
+
+### `$count` — Array/string length
+
+Returns the length of an array or string. Returns `0` for other types.
+
+```json
+{ "$count": { "$state": "/cart/items" } }
+```
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>$count</code></td>
+      <td><code>unknown</code></td>
+      <td>Value to count. Accepts arrays and strings.</td>
+    </tr>
+  </tbody>
+</table>
+
+### `$truncate` — Text truncation
+
+Truncates text to a maximum length with a configurable suffix.
+
+```json
+{ "$truncate": { "$state": "/post/body" }, "length": 140, "suffix": "..." }
+```
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>$truncate</code></td>
+      <td><code>unknown</code></td>
+      <td>Value to truncate.</td>
+    </tr>
+    <tr>
+      <td><code>length</code></td>
+      <td><code>number</code></td>
+      <td>Optional. Max character length. Default: <code>100</code>.</td>
+    </tr>
+    <tr>
+      <td><code>suffix</code></td>
+      <td><code>string</code></td>
+      <td>Optional. Suffix to append when truncated. Default: <code>"..."</code>.</td>
+    </tr>
+  </tbody>
+</table>
+
+### `$pluralize` — Singular/plural forms
+
+Selects a singular, plural, or zero form based on a count.
+
+```json
+{ "$pluralize": { "$state": "/cart/itemCount" }, "one": "item", "other": "items", "zero": "no items" }
+```
+
+Output: `"3 items"`, `"1 item"`, or `"no items"`.
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>$pluralize</code></td>
+      <td><code>unknown</code></td>
+      <td>Count value. Accepts dynamic expressions.</td>
+    </tr>
+    <tr>
+      <td><code>one</code></td>
+      <td><code>string</code></td>
+      <td>Singular form label.</td>
+    </tr>
+    <tr>
+      <td><code>other</code></td>
+      <td><code>string</code></td>
+      <td>Plural form label.</td>
+    </tr>
+    <tr>
+      <td><code>zero</code></td>
+      <td><code>string</code></td>
+      <td>Optional. Label for count of zero. If omitted, uses <code>"0 {'<other>'}"</code>.</td>
+    </tr>
+  </tbody>
+</table>
+
+### `$join` — Join array elements
+
+Joins array elements with a separator string.
+
+```json
+{ "$join": { "$state": "/tags" }, "separator": ", " }
+```
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>$join</code></td>
+      <td><code>unknown</code></td>
+      <td>Array to join. Non-array values are converted to string.</td>
+    </tr>
+    <tr>
+      <td><code>separator</code></td>
+      <td><code>string</code></td>
+      <td>Optional. Separator between elements. Default: <code>", "</code>.</td>
+    </tr>
+  </tbody>
+</table>
+
+### `createI18nDirective` — Internationalization
+
+Factory function that creates a `$t` directive for translations with `{'{{param}}'}` interpolation.
+
+```typescript
+import { createI18nDirective } from '@json-render/directives';
+
+const tDirective = createI18nDirective({
+  locale: 'en',
+  messages: {
+    en: { "greeting": "Hello, {'{{name}}'}!", "checkout.submit": "Place Order" },
+    es: { "greeting": "Hola, {'{{name}}'}!", "checkout.submit": "Realizar Pedido" },
+  },
+  fallbackLocale: 'en',
+});
+```
+
+Usage in specs:
+
+```json
+{ "$t": "checkout.submit" }
+```
+
+```json
+{ "$t": "greeting", "params": { "name": { "$state": "/user/name" } } }
+```
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>$t</code></td>
+      <td><code>string</code></td>
+      <td>Translation key.</td>
+    </tr>
+    <tr>
+      <td><code>params</code></td>
+      <td><code>{'Record<string, unknown>'}</code></td>
+      <td>Optional. Interpolation parameters. Values accept dynamic expressions.</td>
+    </tr>
+  </tbody>
+</table>
+
+#### `I18nConfig`
+
+<table>
+  <thead>
+    <tr>
+      <th>Field</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>locale</code></td>
+      <td><code>string</code></td>
+      <td>Current locale (e.g. <code>"en"</code>).</td>
+    </tr>
+    <tr>
+      <td><code>messages</code></td>
+      <td><code>{'Record<string, Record<string, string>>'}</code></td>
+      <td>Map of locale to key-value translation pairs.</td>
+    </tr>
+    <tr>
+      <td><code>fallbackLocale</code></td>
+      <td><code>string</code></td>
+      <td>Optional. Fallback locale when a key is missing in the current locale.</td>
+    </tr>
+  </tbody>
+</table>
+
+## Composition
+
+Directives compose naturally. Each resolver calls `resolvePropValue` on its inputs, so you can nest directives:
+
+```json
+{
+  "$format": "currency",
+  "value": { "$math": "multiply", "a": { "$state": "/price" }, "b": { "$state": "/qty" } },
+  "currency": "USD"
+}
+```
+
+```json
+{
+  "$pluralize": { "$count": { "$state": "/items" } },
+  "one": "item",
+  "other": "items"
+}
+```

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

@@ -0,0 +1,280 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/next")
+
+# @json-render/next
+
+Next.js renderer. JSON becomes full Next.js applications with routes, layouts, metadata, and SSR.
+
+## Installation
+
+```bash
+npm install @json-render/core @json-render/react @json-render/next
+```
+
+## schema
+
+The Next.js app schema for multi-page specs. Use with `defineCatalog` from core.
+
+```typescript
+import { defineCatalog } from '@json-render/core';
+import { schema } from '@json-render/next/server';
+import { z } from 'zod';
+
+const catalog = defineCatalog(schema, {
+  components: {
+    Card: {
+      props: z.object({ title: z.string() }),
+      description: 'Card container',
+    },
+    NavBar: {
+      props: z.object({ links: z.array(z.object({ href: z.string(), label: z.string() })) }),
+      description: 'Navigation bar',
+    },
+  },
+  actions: {},
+});
+```
+
+## createNextApp
+
+Create all exports needed for a Next.js `[[...slug]]` catch-all route.
+
+```typescript
+import { createNextApp } from '@json-render/next/server';
+
+const { Page, generateMetadata, generateStaticParams } = createNextApp({
+  spec: myAppSpec,
+  loaders: {
+    loadPost: async ({ slug }) => {
+      const post = await db.post.findUnique({ where: { slug } });
+      return { post };
+    },
+  },
+});
+```
+
+### Options
+
+<table>
+  <thead>
+    <tr>
+      <th>Option</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>spec</code></td>
+      <td><code>{'NextAppSpec | (() => NextAppSpec | Promise<NextAppSpec>)'}</code></td>
+      <td>The application spec (static or dynamic)</td>
+    </tr>
+    <tr>
+      <td><code>loaders</code></td>
+      <td><code>{'Record<string, LoaderFn>'}</code></td>
+      <td>Server-side data loaders keyed by name</td>
+    </tr>
+  </tbody>
+</table>
+
+### Returns
+
+<table>
+  <thead>
+    <tr>
+      <th>Export</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>Page</code></td>
+      <td>Async Server Component for <code>page.tsx</code></td>
+    </tr>
+    <tr>
+      <td><code>generateMetadata</code></td>
+      <td>Metadata generator for Next.js SEO</td>
+    </tr>
+    <tr>
+      <td><code>generateStaticParams</code></td>
+      <td>Static params for pre-rendering at build time</td>
+    </tr>
+  </tbody>
+</table>
+
+## NextAppSpec
+
+The top-level spec defining an entire Next.js application.
+
+```typescript
+interface NextAppSpec {
+  metadata?: NextMetadata;
+  routes: Record<string, NextRouteSpec>;
+  layouts?: Record<string, Spec>;
+  state?: Record<string, unknown>;
+}
+```
+
+### Route Patterns
+
+Routes use Next.js URL conventions:
+
+<table>
+  <thead>
+    <tr>
+      <th>Pattern</th>
+      <th>Example Match</th>
+      <th>Params</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>/</code></td>
+      <td><code>/</code></td>
+      <td><code>{'{}'}</code></td>
+    </tr>
+    <tr>
+      <td><code>/about</code></td>
+      <td><code>/about</code></td>
+      <td><code>{'{}'}</code></td>
+    </tr>
+    <tr>
+      <td><code>/blog/[slug]</code></td>
+      <td><code>/blog/hello</code></td>
+      <td><code>{'{ slug: "hello" }'}</code></td>
+    </tr>
+    <tr>
+      <td><code>/docs/[...path]</code></td>
+      <td><code>/docs/a/b/c</code></td>
+      <td><code>{'{ path: ["a","b","c"] }'}</code></td>
+    </tr>
+    <tr>
+      <td><code>/app/[[...path]]</code></td>
+      <td><code>/app</code> or <code>/app/x/y</code></td>
+      <td><code>{'{ path: [] }'}</code> or <code>{'{ path: ["x","y"] }'}</code></td>
+    </tr>
+  </tbody>
+</table>
+
+## NextAppProvider
+
+Client component that provides the component registry and action handlers to all pages.
+
+```tsx
+import { NextAppProvider } from '@json-render/next';
+
+export default function Layout({ children }) {
+  return (
+    <NextAppProvider registry={registry} handlers={handlers}>
+      {children}
+    </NextAppProvider>
+  );
+}
+```
+
+## Built-in Components
+
+### Slot
+
+Placeholder in layouts where page content is rendered. Every layout MUST include a Slot.
+
+```json
+{ "type": "Slot", "props": {}, "children": [] }
+```
+
+### Link
+
+Client-side navigation wrapping `next/link`.
+
+```json
+{ "type": "Link", "props": { "href": "/about" }, "children": ["link-text"] }
+```
+
+## Built-in Actions
+
+<table>
+  <thead>
+    <tr>
+      <th>Action</th>
+      <th>Params</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>setState</code></td>
+      <td><code>{'{ statePath, value }'}</code></td>
+      <td>Update a value in state</td>
+    </tr>
+    <tr>
+      <td><code>pushState</code></td>
+      <td><code>{'{ statePath, value, clearStatePath? }'}</code></td>
+      <td>Append to array in state</td>
+    </tr>
+    <tr>
+      <td><code>removeState</code></td>
+      <td><code>{'{ statePath, index }'}</code></td>
+      <td>Remove from array by index</td>
+    </tr>
+    <tr>
+      <td><code>navigate</code></td>
+      <td><code>{'{ href }'}</code></td>
+      <td>Client-side navigation</td>
+    </tr>
+  </tbody>
+</table>
+
+## Server Utilities
+
+### matchRoute
+
+Match a pathname against a spec's routes.
+
+```typescript
+import { matchRoute } from '@json-render/next/server';
+
+const matched = matchRoute(spec, '/blog/hello-world');
+// { route: NextRouteSpec, pattern: '/blog/[slug]', params: { slug: 'hello-world' } }
+```
+
+### resolveMetadata
+
+Resolve merged metadata for a route.
+
+```typescript
+import { resolveMetadata } from '@json-render/next/server';
+
+const metadata = resolveMetadata(spec, matchedRoute?.route);
+```
+
+### slugToPath
+
+Convert catch-all slug array to pathname.
+
+```typescript
+import { slugToPath } from '@json-render/next/server';
+
+slugToPath(undefined);          // "/"
+slugToPath(['blog', 'hello']);  // "/blog/hello"
+```
+
+## Entry Points
+
+<table>
+  <thead>
+    <tr>
+      <th>Import</th>
+      <th>Contents</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>@json-render/next</code></td>
+      <td>Client components (NextAppProvider, PageRenderer, Link)</td>
+    </tr>
+    <tr>
+      <td><code>@json-render/next/server</code></td>
+      <td>Server utilities (createNextApp, matchRoute, schema)</td>
+    </tr>
+  </tbody>
+</table>

apps/web/app/(main)/docs/api/react-three-fiber/page.mdx

@@ -3,7 +3,7 @@ export const metadata = pageMetadata("docs/api/react-three-fiber")
 
 # @json-render/react-three-fiber
 
-React Three Fiber renderer for json-render. 19 built-in 3D components for meshes, lights, models, environments, text, cameras, and controls.
+React Three Fiber renderer for json-render. 20 built-in 3D components for meshes, lights, models, gaussian splats, environments, text, cameras, and controls.
 
 ## Installation
 
@@ -283,6 +283,11 @@ All primitives share: <code>position</code>, <code>rotation</code>, <code>scale<
 <td>Camera controls</td>
 <td><code>enableDamping</code>, <code>enableZoom</code>, <code>autoRotate</code></td>
 </tr>
+<tr>
+<td><code>GaussianSplat</code></td>
+<td>Gaussian splat (.splat/.ply) loader</td>
+<td><code>src</code>, <code>position</code>, <code>rotation</code>, <code>scale</code>, <code>alphaHash</code>, <code>toneMapped</code></td>
+</tr>
 </tbody>
 </table>
 

apps/web/app/(main)/docs/api/shadcn-svelte/page.mdx

@@ -0,0 +1,320 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/api/shadcn-svelte")
+
+# @json-render/shadcn-svelte
+
+Pre-built [shadcn-svelte](https://www.shadcn-svelte.com/) components for json-render. 36 components built on Svelte 5 + Tailwind CSS, ready to use with `defineCatalog` and `defineRegistry`.
+
+## Installation
+
+```bash
+npm install @json-render/shadcn-svelte @json-render/core @json-render/svelte zod
+```
+
+Your app must have Tailwind CSS configured.
+
+## Entry Points
+
+<table>
+<thead>
+<tr>
+<th>Entry Point</th>
+<th>Exports</th>
+<th>Use For</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><code>@json-render/shadcn-svelte</code></td>
+<td><code>shadcnComponents</code>, <code>shadcnComponentDefinitions</code></td>
+<td>Svelte implementations + catalog schemas</td>
+</tr>
+<tr>
+<td><code>@json-render/shadcn-svelte/catalog</code></td>
+<td><code>shadcnComponentDefinitions</code></td>
+<td>Catalog schemas only (no Svelte dependency, safe for server)</td>
+</tr>
+</tbody>
+</table>
+
+## Usage
+
+Pick the components you need from the standard definitions:
+
+```typescript
+import { defineCatalog } from "@json-render/core";
+import { schema } from "@json-render/svelte/schema";
+import { shadcnComponentDefinitions } from "@json-render/shadcn-svelte/catalog";
+import { defineRegistry } from "@json-render/svelte";
+import { shadcnComponents } from "@json-render/shadcn-svelte";
+
+// Catalog: pick definitions
+const catalog = defineCatalog(schema, {
+  components: {
+    Card: shadcnComponentDefinitions.Card,
+    Stack: shadcnComponentDefinitions.Stack,
+    Heading: shadcnComponentDefinitions.Heading,
+    Button: shadcnComponentDefinitions.Button,
+    Input: shadcnComponentDefinitions.Input,
+  },
+  actions: {},
+});
+
+// Registry: pick matching implementations
+const { registry } = defineRegistry(catalog, {
+  components: {
+    Card: shadcnComponents.Card,
+    Stack: shadcnComponents.Stack,
+    Heading: shadcnComponents.Heading,
+    Button: shadcnComponents.Button,
+    Input: shadcnComponents.Input,
+  },
+});
+```
+
+Then render in your Svelte component:
+
+```svelte
+<script lang="ts">
+  import { Renderer, JsonUIProvider } from "@json-render/svelte";
+
+  export let spec;
+  export let registry;
+</script>
+
+<JsonUIProvider initialState={spec?.state ?? {}}>
+  <Renderer {spec} {registry} />
+</JsonUIProvider>
+```
+
+## Available Components
+
+### Layout
+
+<table>
+<thead>
+<tr>
+<th>Component</th>
+<th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><code>Card</code></td>
+<td>Container card with optional title, description, maxWidth, centered</td>
+</tr>
+<tr>
+<td><code>Stack</code></td>
+<td>Flex container with direction, gap, align, justify</td>
+</tr>
+<tr>
+<td><code>Grid</code></td>
+<td>Grid layout with columns (1-6) and gap</td>
+</tr>
+<tr>
+<td><code>Separator</code></td>
+<td>Visual separator line with orientation</td>
+</tr>
+</tbody>
+</table>
+
+### Navigation
+
+<table>
+<thead>
+<tr>
+<th>Component</th>
+<th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><code>Tabs</code></td>
+<td>Tabbed navigation with tabs array, defaultValue, value</td>
+</tr>
+<tr>
+<td><code>Accordion</code></td>
+<td>Collapsible sections with items array and type (single/multiple)</td>
+</tr>
+<tr>
+<td><code>Collapsible</code></td>
+<td>Single collapsible section with title and defaultOpen</td>
+</tr>
+<tr>
+<td><code>Pagination</code></td>
+<td>Page navigation with totalPages and page</td>
+</tr>
+</tbody>
+</table>
+
+### Overlay
+
+<table>
+<thead>
+<tr>
+<th>Component</th>
+<th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><code>Dialog</code></td>
+<td>Modal dialog with title, description, openPath</td>
+</tr>
+<tr>
+<td><code>Drawer</code></td>
+<td>Bottom drawer with title, description, openPath</td>
+</tr>
+<tr>
+<td><code>Tooltip</code></td>
+<td>Hover tooltip with content and text</td>
+</tr>
+<tr>
+<td><code>Popover</code></td>
+<td>Click-triggered popover with trigger and content</td>
+</tr>
+<tr>
+<td><code>DropdownMenu</code></td>
+<td>Dropdown menu with label and items array</td>
+</tr>
+</tbody>
+</table>
+
+### Content
+
+<table>
+<thead>
+<tr>
+<th>Component</th>
+<th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><code>Heading</code></td>
+<td>Heading text with level (h1-h4)</td>
+</tr>
+<tr>
+<td><code>Text</code></td>
+<td>Paragraph with variant (body, caption, muted, lead, code)</td>
+</tr>
+<tr>
+<td><code>Image</code></td>
+<td>Image with alt, width, height</td>
+</tr>
+<tr>
+<td><code>Avatar</code></td>
+<td>User avatar with src, name, size</td>
+</tr>
+<tr>
+<td><code>Badge</code></td>
+<td>Status badge with text and variant</td>
+</tr>
+<tr>
+<td><code>Alert</code></td>
+<td>Alert banner with title, message, type</td>
+</tr>
+<tr>
+<td><code>Carousel</code></td>
+<td>Horizontally scrollable carousel with items</td>
+</tr>
+<tr>
+<td><code>Table</code></td>
+<td>Data table with columns and rows</td>
+</tr>
+</tbody>
+</table>
+
+### Feedback
+
+<table>
+<thead>
+<tr>
+<th>Component</th>
+<th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><code>Progress</code></td>
+<td>Progress bar with value, max, label</td>
+</tr>
+<tr>
+<td><code>Skeleton</code></td>
+<td>Loading placeholder with width, height, rounded</td>
+</tr>
+<tr>
+<td><code>Spinner</code></td>
+<td>Loading spinner with size and label</td>
+</tr>
+</tbody>
+</table>
+
+### Input
+
+<table>
+<thead>
+<tr>
+<th>Component</th>
+<th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><code>Button</code></td>
+<td>Clickable button with label, variant, disabled</td>
+</tr>
+<tr>
+<td><code>Link</code></td>
+<td>Anchor link with label and href</td>
+</tr>
+<tr>
+<td><code>Input</code></td>
+<td>Text input with label, name, type, placeholder, value, checks</td>
+</tr>
+<tr>
+<td><code>Textarea</code></td>
+<td>Multi-line text input with label, name, placeholder, rows, value, checks</td>
+</tr>
+<tr>
+<td><code>Select</code></td>
+<td>Dropdown select with label, name, options, value, checks</td>
+</tr>
+<tr>
+<td><code>Checkbox</code></td>
+<td>Checkbox with label, name, checked</td>
+</tr>
+<tr>
+<td><code>Radio</code></td>
+<td>Radio button group with label, name, options, value</td>
+</tr>
+<tr>
+<td><code>Switch</code></td>
+<td>Toggle switch with label, name, checked</td>
+</tr>
+<tr>
+<td><code>Slider</code></td>
+<td>Range slider with label, min, max, step, value</td>
+</tr>
+<tr>
+<td><code>Toggle</code></td>
+<td>Toggle button with label, pressed, variant</td>
+</tr>
+<tr>
+<td><code>ToggleGroup</code></td>
+<td>Group of toggle buttons with items, type, value</td>
+</tr>
+<tr>
+<td><code>ButtonGroup</code></td>
+<td>Group of buttons with buttons array and selected</td>
+</tr>
+</tbody>
+</table>
+
+## Notes
+
+- The `/catalog` entry point has no Svelte dependency -- use it for server-side prompt generation
+- Components use Tailwind CSS classes -- your app must have Tailwind configured
+- Component implementations use bundled shadcn-svelte primitives (not your app's `$lib/components/ui/`)
+- Form inputs support `checks` for validation (type + message pairs) and `validateOn` for timing
+- Events: inputs emit `change`/`submit`/`focus`/`blur`; buttons emit `press`; selects emit `change`/`select`

apps/web/app/(main)/docs/api/tanstack-start/page.mdx

@@ -0,0 +1,393 @@
+import { pageMetadata } from "@/lib/page-metadata";
+
+export const metadata = pageMetadata("docs/api/tanstack-start");
+
+# @json-render/tanstack-start
+
+TanStack Start renderer for JSON-defined applications with routes, layouts,
+head metadata, SSR loaders, prerender paths, and client navigation.
+
+## Installation
+
+```bash
+npm install @json-render/core @json-render/react @json-render/tanstack-start
+```
+
+## schema
+
+Use the Start application schema to generate full multi-page specs.
+
+```typescript
+import { defineCatalog } from "@json-render/core";
+import {
+  schema,
+  startComponentDefinitions,
+} from "@json-render/tanstack-start/server";
+import { z } from "zod";
+
+const catalog = defineCatalog(schema, {
+  components: {
+    ...startComponentDefinitions,
+    Card: {
+      props: z.object({ title: z.string() }),
+      description: "Card container",
+    },
+    NavBar: {
+      props: z.object({}),
+      slots: ["default"],
+      description: "Application navigation",
+    },
+  },
+  actions: {},
+});
+```
+
+The generation prompt teaches TanStack Router's `$param` and `$` splat route
+syntax, reusable layouts, escaped JSON Patch route keys, and the built-in
+`Slot`, `Link`, and `navigate` capabilities.
+
+Include `startComponentDefinitions` in the catalog so generated `Slot` and
+`Link` elements pass validation. `PageRenderer` supplies their React
+implementations automatically.
+
+## createStartApp
+
+Create helpers for a TanStack Start splat route.
+
+```typescript
+import { createStartApp } from "@json-render/tanstack-start/server";
+
+export const { getPageData, getHead, getStaticPaths } = createStartApp({
+  spec,
+  loaders: {
+    post: async ({ slug }) => ({
+      post: await getPost(slug as string),
+    }),
+  },
+});
+```
+
+### Options
+
+<table>
+  <thead>
+    <tr>
+      <th>Option</th>
+      <th>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>
+        <code>spec</code>
+      </td>
+      <td>
+        <code>
+          {"StartAppSpec | (() => StartAppSpec | Promise<StartAppSpec>)"}
+        </code>
+      </td>
+      <td>A static application spec or an async spec factory</td>
+    </tr>
+    <tr>
+      <td>
+        <code>loaders</code>
+      </td>
+      <td>
+        <code>{"Record<string, LoaderFn>"}</code>
+      </td>
+      <td>Named data loaders referenced by route specs</td>
+    </tr>
+  </tbody>
+</table>
+
+### Returns
+
+<table>
+  <thead>
+    <tr>
+      <th>Helper</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>
+        <code>getPageData</code>
+      </td>
+      <td>
+        Matches a pathname, runs its loader, and returns serializable page and
+        layout data
+      </td>
+    </tr>
+    <tr>
+      <td>
+        <code>getHead</code>
+      </td>
+      <td>
+        Returns TanStack Router <code>meta</code> and <code>links</code>{" "}
+        descriptors
+      </td>
+    </tr>
+    <tr>
+      <td>
+        <code>getStaticPaths</code>
+      </td>
+      <td>Returns concrete paths for TanStack Start prerendering</td>
+    </tr>
+  </tbody>
+</table>
+
+State is merged in this order: application state, layout state, page state,
+then loader data. Later sources override earlier values.
+
+## StartAppSpec
+
+```typescript
+interface StartAppSpec {
+  metadata?: StartMetadata;
+  routes: Record<string, StartRouteSpec>;
+  layouts?: Record<string, Spec>;
+  state?: Record<string, unknown>;
+}
+```
+
+Each route requires a `page` spec and can select a layout, metadata, a named
+loader, loading/error/not-found specs, and static parameters.
+
+### Route Patterns
+
+<table>
+  <thead>
+    <tr>
+      <th>Pattern</th>
+      <th>Example</th>
+      <th>Params</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>
+        <code>/</code>
+      </td>
+      <td>
+        <code>/</code>
+      </td>
+      <td>
+        <code>{"{}"}</code>
+      </td>
+    </tr>
+    <tr>
+      <td>
+        <code>/about</code>
+      </td>
+      <td>
+        <code>/about</code>
+      </td>
+      <td>
+        <code>{"{}"}</code>
+      </td>
+    </tr>
+    <tr>
+      <td>
+        <code>{"/blog/$slug"}</code>
+      </td>
+      <td>
+        <code>/blog/hello</code>
+      </td>
+      <td>
+        <code>{'{ slug: "hello" }'}</code>
+      </td>
+    </tr>
+    <tr>
+      <td>
+        <code>{"/docs/$"}</code>
+      </td>
+      <td>
+        <code>/docs/guides/intro</code>
+      </td>
+      <td>
+        <code>{'{ _splat: "guides/intro" }'}</code>
+      </td>
+    </tr>
+  </tbody>
+</table>
+
+Loader parameters are URL-decoded before they reach named loaders. Splat
+content is a slash-delimited string under `_splat`. Parameter values supplied
+through `staticParams` are URL-encoded in the paths returned by
+`getStaticPaths()`.
+
+Route matching treats trailing slashes as optional and accepts both encoded and
+decoded pathname representations. This keeps loader data and route metadata in
+sync for static paths containing spaces or non-ASCII characters.
+
+For prerendered dynamic routes, provide `staticParams`:
+
+```typescript
+routes: {
+  '/blog/$slug': {
+    page,
+    staticParams: [{ slug: 'hello' }, { slug: 'world' }],
+  },
+  '/docs/$': {
+    page: docsPage,
+    staticParams: [{ _splat: 'guides/intro' }],
+  },
+}
+```
+
+Map `getStaticPaths()` into TanStack Start's top-level `pages` configuration:
+
+```typescript
+const pages = (await getStaticPaths()).map((path) => ({ path }));
+```
+
+## TanStack Route Setup
+
+Wire the helpers to a file-based `$` splat route:
+
+```tsx
+// src/routes/$.tsx
+import { createFileRoute, notFound } from "@tanstack/react-router";
+import {
+  PageRenderer,
+  StartErrorBoundary,
+  StartLoading,
+  StartNotFound,
+} from "@json-render/tanstack-start";
+import { getHead, getPageData } from "@/lib/json-app";
+
+export const Route = createFileRoute("/$")({
+  loader: async ({ location }) => {
+    const data = await getPageData({ pathname: location.pathname });
+    if (!data) throw notFound();
+    return data;
+  },
+  head: ({ match }) => getHead({ pathname: match.pathname }),
+  component: Page,
+  pendingComponent: StartLoading,
+  errorComponent: StartErrorBoundary,
+  notFoundComponent: StartNotFound,
+});
+
+function Page() {
+  return <PageRenderer {...Route.useLoaderData()} />;
+}
+```
+
+TanStack Router loaders are isomorphic. When a spec factory or named loader
+uses database clients, credentials, or server-only imports, invoke
+`getPageData` and `getHead` inside a TanStack Start `createServerFn` and call
+that server function from the route loader.
+
+## StartAppProvider
+
+Provide component implementations and action handlers around the root
+`Outlet`. Render `HeadContent` for route metadata.
+
+```tsx
+import {
+  createRootRoute,
+  HeadContent,
+  Outlet,
+  Scripts,
+} from "@tanstack/react-router";
+import { StartAppProvider } from "@json-render/tanstack-start";
+import { spec } from "@/lib/spec";
+
+export const Route = createRootRoute({
+  component: () => (
+    <html lang="en">
+      <head>
+        <HeadContent />
+      </head>
+      <body>
+        <StartAppProvider
+          registry={registry}
+          handlers={handlers}
+          spec={spec}
+        >
+          <Outlet />
+        </StartAppProvider>
+        <Scripts />
+      </body>
+    </html>
+  ),
+});
+```
+
+Passing `spec` lets `StartLoading`, `StartErrorBoundary`, and `StartNotFound`
+automatically select the matched route's fallback specs. Their explicit
+`loadingSpec`, `errorSpec`, and `notFoundSpec` props take precedence. For a
+server-only application spec, omit `spec` and pass client-safe fallback specs
+explicitly.
+
+Pass named functions through `functions` when props use `$computed`:
+
+```tsx
+<StartAppProvider
+  registry={registry}
+  spec={spec}
+  functions={{ uppercase: ({ value }) => String(value).toUpperCase() }}
+>
+  <Outlet />
+</StartAppProvider>
+```
+
+## Built-ins
+
+- `Slot` inserts page content into a JSON-defined layout.
+- `Link` wraps TanStack Router's `Link`; generated specs use an `href` prop.
+- `navigate` performs client-side navigation from action bindings.
+- `StartLoading`, `StartErrorBoundary`, and `StartNotFound` resolve the matched
+  route's fallback specs when they are used as TanStack Router boundary
+  components and the provider receives `spec`.
+
+The default `StartErrorBoundary` fallback invalidates the router and reruns the
+failed loader when the user selects **Try again**.
+
+`Slot` and `Link` are automatically added to the page registry.
+
+## Server Utilities
+
+```typescript
+import {
+  collectStaticPaths,
+  matchRoute,
+  metadataToHead,
+  resolveMetadata,
+  splatToPath,
+} from "@json-render/tanstack-start/server";
+```
+
+## Entry Points
+
+<table>
+  <thead>
+    <tr>
+      <th>Import</th>
+      <th>Contents</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>
+        <code>@json-render/tanstack-start</code>
+      </td>
+      <td>Provider, page renderer, Link, and route fallback components</td>
+    </tr>
+    <tr>
+      <td>
+        <code>@json-render/tanstack-start/server</code>
+      </td>
+      <td>App factory, schema, matcher, metadata, and prerender helpers</td>
+    </tr>
+    <tr>
+      <td>
+        <code>@json-render/tanstack-start/catalog</code>
+      </td>
+      <td>Server-safe definitions for built-in Slot and Link components</td>
+    </tr>
+  </tbody>
+</table>

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

@@ -95,7 +95,7 @@ store.set("/count", 1);
 
 ## defineRegistry
 
-Create a type-safe component registry from a catalog. Components receive `props`, `children`, `emit`, `on`, and `loading` with catalog-inferred types.
+Create a type-safe component registry from a catalog. Components receive `props`, `children`, `slots`, `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.
 
@@ -105,8 +105,12 @@ import { defineRegistry } from "@json-render/vue";
 
 const { registry } = defineRegistry(catalog, {
   components: {
-    Card: ({ props, children }) =>
-      h("div", { class: "card" }, [h("h3", null, props.title), children]),
+    Layout: ({ slots }) =>
+      h("div", { class: "layout" }, [
+        h("header", null, slots.header?.()),
+        h("main", null, slots.default?.()),
+        h("footer", null, slots.footer?.()),
+      ]),
     Button: ({ props, emit }) =>
       h("button", { onClick: () => emit("press") }, props.label),
   },
@@ -136,11 +140,12 @@ const { registry } = defineRegistry(catalog, {
 ### Component Props (via defineRegistry)
 
 ```typescript
-import type { VNode } from "vue";
+import type { Slots, VNode } from "vue";
 
 interface ComponentContext<P> {
   props: P;                          // Typed props from catalog
   children?: VNode | VNode[];        // Rendered children (for container components)
+  slots: Slots;                      // Vue-native slot functions
   emit: (event: string) => void;     // Emit a named event (always defined)
   on: (event: string) => EventHandle; // Get event handle with metadata
   loading?: boolean;
@@ -154,6 +159,22 @@ interface EventHandle {
 }
 ```
 
+Use `children` for the default slot. For other slots declared by the catalog, add a top-level `slots` map to the spec element:
+
+```json
+{
+  "type": "Layout",
+  "props": {},
+  "children": ["main-content"],
+  "slots": {
+    "header": ["page-heading"],
+    "footer": ["page-actions"]
+  }
+}
+```
+
+The component renders these regions with Vue's native slot functions: `slots.header?.()`, `slots.footer?.()`, and so on. `slots.default?.()` renders the spec's `children`; `children` is a convenience alias for that rendered result. In the JSON spec, keep default content in `children` rather than adding a `default` entry to `slots`.
+
 Use `emit("press")` for simple event firing. Use `on("click")` when you need metadata like `shouldPreventDefault`:
 
 ```typescript

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

@@ -1,5 +1,5 @@
-import { pageMetadata } from "@/lib/page-metadata"
-export const metadata = pageMetadata("docs/catalog")
+import { pageMetadata } from "@/lib/page-metadata";
+export const metadata = pageMetadata("docs/catalog");
 
 # Catalog
 
@@ -18,9 +18,9 @@ A catalog is the vocabulary for your UI. While the [schema](/docs/schemas) defin
 `defineCatalog` is from `@json-render/core`. The `schema` import comes from your platform package (`@json-render/react` or `@json-render/react-native`) and defines the element structure the catalog targets. The catalog definition itself is framework-agnostic.
 
 ```typescript
-import { defineCatalog } from '@json-render/core';
-import { schema } from '@json-render/react/schema'; // or '@json-render/react-native/schema'
-import { z } from 'zod';
+import { defineCatalog } from "@json-render/core";
+import { schema } from "@json-render/react/schema"; // or '@json-render/react-native/schema'
+import { z } from "zod";
 
 const catalog = defineCatalog(schema, {
   components: {
@@ -29,35 +29,35 @@ const catalog = defineCatalog(schema, {
       props: z.object({
         title: z.string(),
         description: z.string().nullable(),
-        padding: z.enum(['sm', 'md', 'lg']).nullable(),
+        padding: z.enum(["sm", "md", "lg"]).nullable(),
       }),
       slots: ["default"], // Can contain other components
       description: "Container card for grouping content",
     },
-    
+
     Metric: {
       props: z.object({
         label: z.string(),
         value: z.union([z.string(), z.number()]),
-        format: z.enum(['currency', 'percent', 'number']),
+        format: z.enum(["currency", "percent", "number"]),
       }),
       description: "Display a single metric value",
     },
   },
-  
+
   actions: {
     submit_form: {
       params: z.object({
         formId: z.string(),
       }),
-      description: 'Submit a form',
+      description: "Submit a form",
     },
-    
+
     export_data: {
       params: z.object({
-        format: z.enum(['csv', 'pdf', 'json']),
+        format: z.enum(["csv", "pdf", "json"]),
       }),
-      description: 'Export data in various formats',
+      description: "Export data in various formats",
     },
   },
 });
@@ -70,12 +70,22 @@ Each component in the catalog has:
 ```typescript
 {
   props: z.object({...}),  // Zod schema for props (use .nullable() for optional)
-  slots?: string[],        // Named slots for children (e.g., ["default"])
+  slots?: string[],        // Available slots (e.g., ["default", "header", "footer"])
   description?: string,    // Help AI understand when to use it
 }
 ```
 
-Use `slots: ["default"]` for components that can contain children. The slot name corresponds to where child elements are rendered.
+Use `"default"` for regular children. Add named slots when a component places content in multiple regions:
+
+```typescript
+Layout: {
+  props: z.object({}),
+  slots: ["default", "header", "footer"],
+  description: "Page layout with header, content, and footer regions",
+}
+```
+
+React specs use `children` for the default slot and a `slots` object for the other names.
 
 ## Generating AI Prompts
 

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

@@ -5,9 +5,338 @@ export const metadata = pageMetadata("docs/changelog")
 
 Notable changes and updates to json-render.
 
+## v0.20.0
+
+August 15, 2026
+
+### New: Named Slots for React
+
+React components can now declare named slots such as `header` and `footer`, while `children` remains the default slot. Named slots are preserved through validation, streaming, nested conversion, code export, playground views, and Devtools navigation.
+
+This work builds on the original named slots contribution by @wotnak.
+
+```tsx
+const catalog = defineCatalog(schema, {
+  components: {
+    Layout: {
+      props: z.object({}),
+      slots: ["default", "header", "footer"],
+    },
+  },
+});
+
+const { registry } = defineRegistry(catalog, {
+  components: {
+    Layout: ({ children, slots }) => (
+      <section>
+        <header>{slots?.header}</header>
+        <main>{children}</main>
+        <footer>{slots?.footer}</footer>
+      </section>
+    ),
+  },
+});
+```
+
+### New: Nested Repeats
+
+`repeat.statePath` now accepts item-relative paths such as `{ "$item": "employees" }`. Nested data can be rendered across React, React Native, React Email, React PDF, Image, Ink, Solid, Svelte, and Vue.
+
+This work builds on the original nested repeats contribution by @tmchow.
+
+```json
+{
+  "type": "Table",
+  "repeat": { "statePath": { "$item": "employees" }, "key": "id" },
+  "children": ["employee-row"],
+  "props": {}
+}
+```
+
+### New: Harness Chat Example
+
+Added a complete Next.js example using the AI SDK 7 harness adapter, agent delegation, sandbox transport, and json-render components.
+
+### Fixed: Chained Action Params
+
+Named `onSuccess` and `onError` actions now receive their configured `params` across core and all renderer bridges. Custom renderer bridges must now accept an `ActionBinding` in the core `executeAction` callback instead of a bare action name.
+
+### Improved: Spec Validation and Compatibility
+
+Element visibility remains optional across Zod 4 versions. Autofix now prunes dangling child references, validation reports malformed visibility conditions, and repeated items can be filtered safely.
+
+### Improved: Release Toolchain
+
+The workspace now requires Node.js 24 and pnpm 11, enforces package engine checks, and applies a minimum package release age.
+
+---
+
+## v0.19.0
+
+May 6, 2026
+
+### New: Custom Directives API
+
+`@json-render/core` now supports custom directives via `defineDirective`, letting you declare new JSON shapes (like `$format`, `$math`) that resolve to computed values at render time. Directives compose naturally -- nest `$format` over `$math` over `$state` and they resolve inside-out. All four renderers (React, Vue, Svelte, Solid) have built-in directive resolution.
+
+### New: `@json-render/directives`
+
+New package shipping seven ready-made directives: `$format` (date, currency, number, percent via `Intl`), `$math` (arithmetic and rounding), `$concat`, `$count`, `$truncate`, `$pluralize`, and `$join`. Also exports `createI18nDirective` for `$t` translation keys with interpolation, and `standardDirectives` for one-line registration.
+
+```bash
+npm install @json-render/directives
+```
+
+```tsx
+import { standardDirectives } from "@json-render/directives";
+
+const catalog = createCatalog({
+  directives: standardDirectives,
+  // ...
+});
+```
+
+See the [Directives guide](/docs/directives) and the [API reference](/docs/api/directives) for details.
+
+---
+
+## v0.18.0
+
+April 17, 2026
+
+### New: Devtools
+
+Five new packages for inspecting json-render apps in the browser:
+
+- `@json-render/devtools` -- framework-agnostic core
+- `@json-render/devtools-react`
+- `@json-render/devtools-vue`
+- `@json-render/devtools-svelte`
+- `@json-render/devtools-solid`
+
+Drop `<JsonRenderDevtools />` into your app to get a shadow-DOM-isolated panel with six tabs (Spec, State, Actions, Stream, Catalog, Pick), a DOM picker that maps clicked elements back to spec keys via `data-jr-key`, and a capped event store. Toggle with the floating button or `Cmd`/`Ctrl` + `Shift` + `J`. Tree-shakes to `null` in production.
+
+```bash
+npm install @json-render/devtools-react
+```
+
+```tsx
+import { JsonRenderDevtools } from "@json-render/devtools-react";
+
+<JsonRenderDevtools />
+```
+
+See the [Devtools guide](/docs/devtools) and the [API reference](/docs/api/devtools) for details.
+
+### New: Devtools Example
+
+New `examples/devtools` Next.js demo showing the full devtools panel wired up to an AI chat endpoint and a component catalog.
+
+### New: Action Observer and Devtools Flag in Core
+
+`@json-render/core` now exposes an action observer and a devtools enablement flag that framework adapters use to mirror actions and stream events into the panel.
+
+### Fixed: Zod 4 Schema Formatting
+
+`formatZodType` now correctly handles `z.record()`, `z.default()`, and `z.literal()` types from Zod 4, which previously produced incorrect or empty output in generated prompts and schemas.
+
+---
+
+## v0.17.0
+
+April 10, 2026
+
+### New: Gaussian Splatting
+
+Added `GaussianSplat` component to `@json-render/react-three-fiber`, bringing the component count to 20. Composable with all existing R3F components (lights, controls, post-processing) via drei's Splat loader.
+
+### New: R3F Gaussian Splatting Example
+
+Demo app with five scenes: splat showroom, splat with primitives, multi-splat, post-processing effects, and animated floating splat.
+
+### New: Standalone gsplat Example
+
+Experimental demo app showcasing Gaussian Splatting with gsplat.js (no Three.js dependency), featuring scene selector, live JSON spec viewer, and progress indicator.
+
+### Improved: AI Output Quality
+
+Improved prompt output and schema generation for more reliable AI-generated specs.
+
+---
+
+## v0.16.0
+
+March 27, 2026
+
+### New: `@json-render/next`
+
+Next.js renderer that turns JSON specs into full Next.js applications with routes, layouts, SSR, metadata, data loaders, and static generation. Client and server entry points at `@json-render/next` and `@json-render/next/server`. Includes built-in `Link`, `Slot`, error boundary, loading, and not-found components.
+
+```bash
+npm install @json-render/next
+```
+
+### New: `@json-render/shadcn-svelte`
+
+Pre-built shadcn-svelte components for json-render Svelte apps. 36 components built on Svelte 5 + Tailwind CSS with state binding, validation, and action support. Server-safe catalog at `@json-render/shadcn-svelte/catalog`.
+
+```bash
+npm install @json-render/shadcn-svelte
+```
+
+### Improved: Release Process
+
+Switched from Changesets to a manual single-PR release workflow with changelog markers and automatic npm publish on version bump.
+
+---
+
+## v0.15.0
+
+March 23, 2026
+
+### New: `@json-render/ink`
+
+Terminal renderer for json-render. JSON becomes terminal UIs powered by [Ink](https://github.com/vadimdemedes/ink). Stream AI-generated specs directly to the terminal with `useUIStream`.
+
+```bash
+npm install @json-render/ink
+```
+
+### Improved: YAML Format Support in `buildUserPrompt`
+
+`buildUserPrompt` now accepts `format` and `serializer` options, enabling YAML as a wire format alongside JSON.
+
+---
+
+## v0.14.0
+
+March 13, 2026
+
+### New: `@json-render/yaml`
+
+YAML wire format for json-render. Includes streaming YAML parser, `yamlPrompt()` for system prompts, and AI SDK transform (`pipeYamlRender`) as a drop-in alternative to JSONL streaming. Supports four fence types: `yaml-spec`, `yaml-edit`, `yaml-patch`, and `diff`.
+
+```bash
+npm install @json-render/yaml
+```
+
+### New: Universal Edit Modes
+
+Three strategies for multi-turn spec refinement in `@json-render/core`:
+
+- **Patch** -- RFC 6902 JSON Patch
+- **Merge** -- RFC 7396 Merge Patch
+- **Diff** -- Unified diff
+
+New `editModes` option on `buildUserPrompt()` and `PromptOptions`. New helpers: `deepMergeSpec()`, `diffToPatches()`, `buildEditUserPrompt()`, `buildEditInstructions()`, `isNonEmptySpec()`.
+
+### Improved: Playground
+
+Format toggle (JSONL / YAML), edit mode picker (patch / merge / diff), and token usage display with prompt caching stats.
+
+### Improved: Prompt Caching
+
+Generate API uses Anthropic ephemeral cache control for system prompts.
+
+---
+
+## v0.13.0
+
+March 12, 2026
+
+### New: `@json-render/solid`
+
+SolidJS renderer for json-render. JSON becomes Solid components with reactive rendering, schema export, and full catalog support.
+
+```bash
+npm install @json-render/core @json-render/solid
+```
+
+### New: `@json-render/react-three-fiber`
+
+React Three Fiber renderer for json-render. JSON becomes 3D scenes with 19 built-in components for meshes, lights, models, environments, text, cameras, and controls.
+
+```bash
+npm install @json-render/react-three-fiber
+```
+
+### Improved: Strict JSON Schema Mode
+
+`catalog.jsonSchema({ strict: true })` produces a JSON Schema subset compatible with LLM structured output APIs (OpenAI, Google Gemini, Anthropic). Ensures `additionalProperties: false` on every object and all properties listed in `required`.
+
+---
+
+## v0.12.1
+
+March 11, 2026
+
+### Changed: Generation Mode Renames
+
+Renamed generation modes from `"generate"` / `"chat"` to `"standalone"` / `"inline"`. The old names still work but emit a deprecation warning.
+
+### Fixed: MCP React Duplicate Module Error
+
+Resolved React duplicate module error (`useRef` returning null) in `@json-render/mcp` by adding `resolve.dedupe` Vite configuration. Added `./build-app-html` export entry point.
+
+---
+
+## v0.12.0
+
+March 6, 2026
+
+### New: `@json-render/svelte`
+
+Svelte 5 renderer with runes-based reactivity. Full support for data binding, visibility, actions, validation, watchers, streaming, and repeat scopes. Includes `defineRegistry`, `Renderer`, `schema`, composables, and context providers.
+
+```bash
+npm install @json-render/core @json-render/svelte
+```
+
+### New: `@json-render/react-email`
+
+React Email renderer for generating HTML and plain-text emails from JSON specs. 17 standard components (Html, Head, Body, Container, Section, Row, Column, Heading, Text, Link, Button, Image, Hr, Preview, Markdown). Server-side `renderToHtml` / `renderToPlainText` APIs.
+
+```bash
+npm install @json-render/react-email
+```
+
+### New: `@json-render/mcp`
+
+MCP Apps integration that serves json-render UIs as interactive apps inside Claude, ChatGPT, Cursor, VS Code, and other MCP-capable clients. `createMcpApp` server factory, `useJsonRenderApp` React hook for iframes, and `buildAppHtml` utility.
+
+```bash
+npm install @json-render/mcp
+```
+
+---
+
+## v0.11.0
+
+February 27, 2026
+
+### New: `@json-render/image`
+
+Server-side image renderer powered by Satori. Turns the same `{ root, elements }` spec format into SVG or PNG output for OG images, social cards, and banners.
+
+```bash
+npm install @json-render/image
+```
+
+```typescript
+import { renderToSvg, renderToPng } from "@json-render/image/render";
+import { standardComponentDefinitions } from "@json-render/image/catalog";
+
+const svg = await renderToSvg(spec, { width: 1200, height: 630 });
+const png = await renderToPng(spec, { width: 1200, height: 630 });
+```
+
+9 standard components: Frame, Box, Row, Column, Heading, Text, Image, Divider, Spacer. Server-safe import path at `@json-render/image/server`.
+
+---
+
 ## v0.10.0
 
-February 2026
+February 25, 2026
 
 ### New: `@json-render/vue`
 
@@ -120,7 +449,7 @@ All form components now support `checks` and `validateOn` props:
 
 ## v0.9.1
 
-February 2026
+February 24, 2026
 
 ### Fixed: Install failure due to private dependency
 
@@ -130,7 +459,7 @@ February 2026
 
 ## v0.9.0
 
-February 2026
+February 24, 2026
 
 ### New: External State Store
 
@@ -184,7 +513,7 @@ Fixed safely resolving the inner type for Zod arrays in schema introspection, pr
 
 ## v0.8.0
 
-February 2026
+February 20, 2026
 
 ### New: `@json-render/react-pdf`
 
@@ -246,7 +575,7 @@ Supports custom catalogs with `defineRegistry`, server-safe imports via `@json-r
 
 ## v0.7.0
 
-February 2026
+February 17, 2026
 
 ### New: `@json-render/shadcn`
 
@@ -337,7 +666,7 @@ Action bindings now support a `preventDefault` boolean field, allowing the LLM t
 
 ## v0.6.0
 
-February 2026
+February 13, 2026
 
 ### New: Chat Mode (Inline GenUI)
 
@@ -479,7 +808,7 @@ See the [Migration Guide](/docs/migration) for detailed upgrade instructions.
 
 ## v0.5.0
 
-February 2026
+February 9, 2026
 
 ### New: @json-render/react-native
 
@@ -598,7 +927,7 @@ Schema prompts now include streaming best practices, repeat/list examples, and s
 
 ## v0.4.0
 
-February 2026
+February 5, 2026
 
 ### New: Custom Schema System
 
@@ -733,7 +1062,7 @@ The dashboard example is now a full-featured accounting dashboard with:
 
 ## v0.3.0
 
-January 2026
+January 20, 2026
 
 Internal release with codegen foundations.
 
@@ -747,7 +1076,7 @@ Internal release with codegen foundations.
 
 ## v0.2.0
 
-January 2026
+January 14, 2026
 
 Initial public release.
 

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

@@ -126,7 +126,7 @@ The `repeat` field on an element renders its children once per item in a state a
 }
 ```
 
-- `repeat.statePath` — JSON Pointer to the state array
+- `repeat.statePath`: root JSON Pointer to the state array, or `{ "$item": "field" }` for an array on the enclosing repeat item
 - `repeat.key` — field name on each item to use as a stable key for rendering
 
 Inside `todo-item`, `{ "$item": "title" }` reads the `title` field from whichever array item is currently being rendered. `{ "$index": true }` would return `0` for the first item, `1` for the second, and so on.

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

@@ -0,0 +1,207 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/devtools")
+
+# Devtools
+
+A drop-in inspector panel for any json-render app. See the spec tree, edit state inline, watch dispatched actions, follow stream patches live, browse your catalog, and pick DOM elements to map them back to spec keys.
+
+Production-safe: the component tree-shakes to a null render when `NODE_ENV === "production"`.
+
+## Install
+
+Pick the adapter that matches your renderer.
+
+### React
+
+```bash
+npm install @json-render/devtools @json-render/devtools-react
+```
+
+### Vue
+
+```bash
+npm install @json-render/devtools @json-render/devtools-vue
+```
+
+### Svelte
+
+```bash
+npm install @json-render/devtools @json-render/devtools-svelte
+```
+
+### Solid
+
+```bash
+npm install @json-render/devtools @json-render/devtools-solid
+```
+
+## Quick Start
+
+Drop `<JsonRenderDevtools />` anywhere inside your existing `<JSONUIProvider>` (or the equivalent provider tree).
+
+```tsx
+// React
+import { JsonRenderDevtools } from "@json-render/devtools-react";
+
+<JSONUIProvider registry={registry} handlers={handlers}>
+  <Renderer spec={spec} registry={registry} />
+  <JsonRenderDevtools spec={spec} catalog={catalog} />
+</JSONUIProvider>
+```
+
+That's it. A floating toggle appears in the bottom-right corner. Click it, or press <kbd>Ctrl</kbd>/<kbd>Cmd</kbd> + <kbd>Shift</kbd> + <kbd>J</kbd>, to open the drawer.
+
+### Chat apps (AI SDK)
+
+When you're using `@ai-sdk/react`'s `useChat`, pass the `messages` prop so the Stream tab captures spec patches as they arrive:
+
+```tsx
+<JsonRenderDevtools
+  spec={spec}
+  catalog={catalog}
+  messages={messages}
+/>
+```
+
+## Panels
+
+<table>
+  <thead>
+    <tr><th>Tab</th><th>What it shows</th></tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><strong>Spec</strong></td>
+      <td>Element tree rooted at <code>spec.root</code>. Expand to walk children. Selecting an element fills a detail pane with its full props, visibility condition, event bindings, watchers, and any issues reported by <code>validateSpec</code>.</td>
+    </tr>
+    <tr>
+      <td><strong>State</strong></td>
+      <td>Every leaf path in the state model listed via <code>flattenToPointers</code>. Click a value to edit inline — writes go through <code>store.set</code>, so conditional elements and computed props re-evaluate immediately.</td>
+    </tr>
+    <tr>
+      <td><strong>Actions</strong></td>
+      <td>Timeline of dispatched actions: name, params, result or error, duration. Newest first. Expand a row for the full JSON payload.</td>
+    </tr>
+    <tr>
+      <td><strong>Stream</strong></td>
+      <td>Patches, text chunks, token usage, and lifecycle markers from the AI generation stream. Grouped by generation.</td>
+    </tr>
+    <tr>
+      <td><strong>Catalog</strong></td>
+      <td>Components and actions declared in your catalog with prop chips and type hints.</td>
+    </tr>
+    <tr>
+      <td><strong>Pick</strong></td>
+      <td>Click any element in the page to surface its entry in the Spec tab. Works because the renderer transparently tags each element with <code>data-jr-key</code> while devtools is mounted.</td>
+    </tr>
+  </tbody>
+</table>
+
+## Props
+
+<table>
+  <thead>
+    <tr><th>Prop</th><th>Type</th><th>Default</th><th>Description</th></tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>spec</code></td>
+      <td><code>Spec | null</code></td>
+      <td><code>null</code></td>
+      <td>The spec currently being rendered.</td>
+    </tr>
+    <tr>
+      <td><code>catalog</code></td>
+      <td><code>Catalog | null</code></td>
+      <td><code>null</code></td>
+      <td>Catalog definition — required for the Catalog panel.</td>
+    </tr>
+    <tr>
+      <td><code>messages</code></td>
+      <td><code>UIMessage[]</code></td>
+      <td><code>undefined</code></td>
+      <td>AI SDK <code>useChat</code> messages. Scanned for spec data parts and streamed into the Stream panel.</td>
+    </tr>
+    <tr>
+      <td><code>initialOpen</code></td>
+      <td><code>boolean</code></td>
+      <td><code>false</code></td>
+      <td>Start the drawer open.</td>
+    </tr>
+    <tr>
+      <td><code>position</code></td>
+      <td><code>"bottom-right" | "bottom-left" | "right"</code></td>
+      <td><code>"bottom-right"</code></td>
+      <td>Floating toggle button position.</td>
+    </tr>
+    <tr>
+      <td><code>hotkey</code></td>
+      <td><code>string | false</code></td>
+      <td><code>"mod+shift+j"</code></td>
+      <td>Keyboard shortcut. Use <code>mod</code> for Cmd on macOS / Ctrl elsewhere. Pass <code>false</code> to disable.</td>
+    </tr>
+    <tr>
+      <td><code>bufferSize</code></td>
+      <td><code>number</code></td>
+      <td><code>500</code></td>
+      <td>Max events retained in the ring buffer.</td>
+    </tr>
+    <tr>
+      <td><code>onEvent</code></td>
+      <td><code>(evt: DevtoolsEvent) =&gt; void</code></td>
+      <td><code>undefined</code></td>
+      <td>Optional tap — fires for every event as it is recorded. Useful for forwarding to analytics.</td>
+    </tr>
+  </tbody>
+</table>
+
+## Production Safety
+
+The component renders `null` when `process.env.NODE_ENV === "production"`. Bundlers fold the constant check so the panel's code tree-shakes out of production builds.
+
+If you want extra certainty, gate the import behind an env check:
+
+```tsx
+import dynamic from "next/dynamic";
+
+const JsonRenderDevtools = dynamic(
+  () =>
+    import("@json-render/devtools-react").then((m) => ({
+      default: m.JsonRenderDevtools,
+    })),
+  { ssr: false, loading: () => null },
+);
+```
+
+## Advanced
+
+### Imperative controls
+
+Use `useJsonRenderDevtools()` (React adapter only) to open / close the panel or record custom events from anywhere in the app:
+
+```tsx
+import { useJsonRenderDevtools } from "@json-render/devtools-react";
+
+function DebugButton() {
+  const devtools = useJsonRenderDevtools();
+  return (
+    <button onClick={() => devtools?.toggle()}>Toggle devtools</button>
+  );
+}
+```
+
+### Server-side stream tap
+
+Capture stream events before they reach the client. Useful for server logs:
+
+```ts
+import { tapJsonRenderStream } from "@json-render/devtools";
+
+const tapped = tapJsonRenderStream(
+  result.toUIMessageStream(),
+  serverEventStore,
+);
+writer.merge(pipeJsonRender(tapped));
+```
+
+The `@json-render/devtools` core package exports `tapJsonRenderStream` and `tapYamlStream` for this pattern.

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

@@ -0,0 +1,124 @@
+import { pageMetadata } from "@/lib/page-metadata"
+export const metadata = pageMetadata("docs/directives")
+
+# Directives
+
+Extend the spec language with custom `$`-prefixed dynamic values. Directives let you add formatting, math, string manipulation, i18n, and any other transformation without modifying core.
+
+## Overview
+
+A directive is a user-defined dynamic value expression, like `$state` or `$computed`, but defined in userland. Each directive has a `$`-prefixed name, a Zod schema for validation, and a resolver function.
+
+```json
+{
+  "type": "Text",
+  "props": {
+    "text": {
+      "$format": "currency",
+      "value": { "$state": "/cart/total" },
+      "currency": "USD"
+    }
+  },
+  "children": []
+}
+```
+
+## Defining a Directive
+
+Use `defineDirective` from `@json-render/core`:
+
+```typescript
+import { defineDirective, resolvePropValue } from '@json-render/core';
+import { z } from 'zod';
+
+const doubleDirective = defineDirective({
+  name: '$double',
+  description: 'Double a numeric value.',
+  schema: z.object({
+    $double: z.unknown(),
+  }),
+  resolve(value, ctx) {
+    const resolved = resolvePropValue(value.$double, ctx);
+    return (resolved as number) * 2;
+  },
+});
+```
+
+The `description` field is optional. When generating prompts, the directive's schema fields are auto-described from the Zod schema; the `description` adds short behavioral context the schema can't express.
+
+## Wiring Directives
+
+Pass directives to both the renderer (for runtime resolution) and the catalog prompt (for AI generation).
+
+### Runtime
+
+```tsx
+import { JSONUIProvider, Renderer } from '@json-render/react';
+import { standardDirectives } from '@json-render/directives';
+
+<JSONUIProvider registry={registry} directives={standardDirectives}>
+  <Renderer spec={spec} registry={registry} />
+</JSONUIProvider>
+```
+
+Or with `createRenderer`:
+
+```tsx
+const MyRenderer = createRenderer(catalog, components);
+
+<MyRenderer spec={spec} directives={directives} />
+```
+
+All four renderers (React, Vue, Svelte, Solid) accept the `directives` prop on their provider and `createRenderer` output.
+
+### Prompt Generation
+
+```typescript
+const prompt = catalog.prompt({ directives });
+```
+
+Each directive's schema is auto-described in the "CUSTOM DYNAMIC VALUES" section of the system prompt. The optional `description` field adds behavioral context inline.
+
+## Pre-built Directives
+
+The `@json-render/directives` package ships ready-to-use directives:
+
+```typescript
+import { standardDirectives, createI18nDirective } from '@json-render/directives';
+```
+
+`standardDirectives` includes `$format`, `$math`, `$concat`, `$count`, `$truncate`, `$pluralize`, and `$join`. Add factory directives by spreading:
+
+```typescript
+const directives = [...standardDirectives, createI18nDirective(config)];
+```
+
+See the [API reference](/docs/api/directives) for details on each directive.
+
+## Composition
+
+Directives compose naturally. Each resolver calls `resolvePropValue` on its inputs, so directives can wrap other directives or built-in expressions like `$state`:
+
+```json
+{
+  "$format": "currency",
+  "value": {
+    "$math": "multiply",
+    "a": { "$state": "/price" },
+    "b": { "$state": "/qty" }
+  },
+  "currency": "USD"
+}
+```
+
+This resolves inside-out: `$state` reads from state, `$math` multiplies the values, and `$format` formats the result as currency.
+
+## Built-in Precedence
+
+Built-in expressions (`$state`, `$computed`, `$cond`, `$template`, etc.) always take precedence over custom directives. `defineDirective` throws if you try to register a name that conflicts with a built-in key.
+
+## Next
+
+- [API Reference](/docs/api/directives) — full directive reference
+- [Computed Values](/docs/computed-values) — `$computed` and `$template` expressions
+- [Data Binding](/docs/data-binding) — `$state`, `$item`, and binding expressions

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

@@ -1,9 +1,9 @@
-import { pageMetadata } from "@/lib/page-metadata"
-export const metadata = pageMetadata("docs/registry")
+import { pageMetadata } from "@/lib/page-metadata";
+export const metadata = pageMetadata("docs/registry");
 
 # Registry
 
-A registry maps your [catalog](/docs/catalog) definitions to platform-specific implementations. The catalog defines *what* AI can generate — the registry provides the *how*.
+A registry maps your [catalog](/docs/catalog) definitions to platform-specific implementations. The catalog defines _what_ AI can generate; the registry provides the _how_.
 
 What a registry contains depends on the schema you use. Each package defines its own schema, which determines the shape of both the catalog and the registry.
 
@@ -19,8 +19,8 @@ What a registry contains depends on the schema you use. Each package defines its
 Use `defineRegistry` to create a type-safe registry from your catalog. Pass your components, actions, or both:
 
 ```tsx
-import { defineRegistry } from '@json-render/react';
-import { myCatalog } from './catalog';
+import { defineRegistry } from "@json-render/react";
+import { myCatalog } from "./catalog";
 
 export const { registry, handlers, executeAction } = defineRegistry(myCatalog, {
   components: {
@@ -33,16 +33,14 @@ export const { registry, handlers, executeAction } = defineRegistry(myCatalog, {
     ),
 
     Button: ({ props, emit }) => (
-      <button onClick={() => emit("press")}>
-        {props.label}
-      </button>
+      <button onClick={() => emit("press")}>{props.label}</button>
     ),
   },
 
   actions: {
     submit_form: async (params, setState) => {
-      const res = await fetch('/api/submit', {
-        method: 'POST',
+      const res = await fetch("/api/submit", {
+        method: "POST",
         body: JSON.stringify(params),
       });
       const result = await res.json();
@@ -69,23 +67,36 @@ Each component receives a `ComponentContext` object:
 
 ```typescript
 interface ComponentContext {
-  props: T;                                // Type-safe props from your catalog
-  children?: React.ReactNode;              // Rendered children (for slot components)
-  emit: (event: string) => void;           // Emit a named event (always defined)
-  on: (event: string) => EventHandle;      // Get event handle with metadata
-  loading?: boolean;                       // Whether the renderer is in a loading state
-  bindings?: Record<string, string>;       // State paths from $bindState/$bindItem expressions
+  props: T; // Type-safe props from your catalog
+  children?: React.ReactNode; // Rendered children (for slot components)
+  slots?: Record<string, React.ReactNode>; // Rendered named slots
+  emit: (event: string) => void; // Emit a named event (always defined)
+  on: (event: string) => EventHandle; // Get event handle with metadata
+  loading?: boolean; // Whether the renderer is in a loading state
+  bindings?: Record<string, string>; // State paths from $bindState/$bindItem expressions
 }
 
 interface EventHandle {
-  emit: () => void;              // Fire the event
+  emit: () => void; // Fire the event
   shouldPreventDefault: boolean; // Whether any binding requested preventDefault
-  bound: boolean;                // Whether any handler is bound
+  bound: boolean; // Whether any handler is bound
 }
 ```
 
 Props are automatically inferred from your catalog, so `props.title` is typed as `string` if your catalog defines it that way.
 
+For components with named slots, read the default content from `children` and other regions from `slots`:
+
+```tsx
+Layout: ({ children, slots }) => (
+  <div>
+    <header>{slots?.header}</header>
+    <main>{children}</main>
+    <footer>{slots?.footer}</footer>
+  </div>
+),
+```
+
 Use `emit("press")` for simple event firing. Use `on("click")` when you need to inspect event metadata:
 
 ```tsx
@@ -128,27 +139,29 @@ TextInput: ({ props, bindings }) => {
 
 ### Action Handlers
 
-Instead of AI generating arbitrary code, it declares *intent* by name. Your application provides the implementation. This is a core guardrail.
+Instead of AI generating arbitrary code, it declares _intent_ by name. Your application provides the implementation. This is a core guardrail.
 
 Actions are declared in your [catalog](/docs/catalog). The `@json-render/react` schema supports an `actions` key where you define what operations AI can trigger:
 
 ```typescript
-import { defineCatalog } from '@json-render/core';
-import { schema } from '@json-render/react/schema';
-import { z } from 'zod';
+import { defineCatalog } from "@json-render/core";
+import { schema } from "@json-render/react/schema";
+import { z } from "zod";
 
 const catalog = defineCatalog(schema, {
-  components: { /* ... */ },
+  components: {
+    /* ... */
+  },
   actions: {
     submit_form: {
       params: z.object({
         formId: z.string(),
       }),
-      description: 'Submit a form',
+      description: "Submit a form",
     },
     export_data: {
       params: z.object({
-        format: z.enum(['csv', 'pdf', 'json']),
+        format: z.enum(["csv", "pdf", "json"]),
       }),
     },
     navigate: {
@@ -166,8 +179,8 @@ Action handlers receive `(params, setState, state)` and are defined inside `defi
 export const { handlers, executeAction } = defineRegistry(catalog, {
   actions: {
     submit_form: async (params, setState) => {
-      const response = await fetch('/api/submit', {
-        method: 'POST',
+      const response = await fetch("/api/submit", {
+        method: "POST",
         body: JSON.stringify({ formId: params.formId }),
       });
       const result = await response.json();
@@ -219,14 +232,14 @@ For read-only state access (e.g. displaying a value from state), use `$state` ex
 Wire everything together with providers and the `<Renderer />` component:
 
 ```tsx
-import { useMemo, useRef } from 'react';
+import { useMemo, useRef } from "react";
 import {
   Renderer,
   StateProvider,
   VisibilityProvider,
   ActionProvider,
-} from '@json-render/react';
-import { registry, handlers } from './registry';
+} from "@json-render/react";
+import { registry, handlers } from "./registry";
 
 function App({ spec, state, setState }) {
   const stateRef = useRef(state);
@@ -235,7 +248,11 @@ function App({ spec, state, setState }) {
   setStateRef.current = setState;
 
   const actionHandlers = useMemo(
-    () => handlers(() => setStateRef.current, () => stateRef.current),
+    () =>
+      handlers(
+        () => setStateRef.current,
+        () => stateRef.current,
+      ),
     [],
   );
 
@@ -256,8 +273,8 @@ function App({ spec, state, setState }) {
 `@json-render/react-native` uses the same `defineRegistry` API. The only difference is that components return React Native elements instead of HTML:
 
 ```tsx
-import { defineRegistry } from '@json-render/react-native';
-import { View, Text, Pressable } from 'react-native';
+import { defineRegistry } from "@json-render/react-native";
+import { View, Text, Pressable } from "react-native";
 
 export const { registry } = defineRegistry(catalog, {
   components: {
@@ -284,14 +301,14 @@ See the [@json-render/react-native API reference](/docs/api/react-native) for th
 `@json-render/react-email` uses `defineRegistry` like React and React Native. Components render to React Email primitives (`@react-email/components`). Use `renderToHtml` or `renderToPlainText` for server-side email output:
 
 ```tsx
-import { defineRegistry } from '@json-render/react-email';
-import { renderToHtml } from '@json-render/react-email';
-import { Body, Container, Heading, Text } from '@react-email/components';
+import { defineRegistry } from "@json-render/react-email";
+import { renderToHtml } from "@json-render/react-email";
+import { Body, Container, Heading, Text } from "@react-email/components";
 
 export const { registry } = defineRegistry(catalog, {
   components: {
     Card: ({ props, children }) => (
-      <Container style={{ padding: 16, backgroundColor: '#fff' }}>
+      <Container style={{ padding: 16, backgroundColor: "#fff" }}>
         <Heading>{props.title}</Heading>
         {children}
       </Container>
@@ -309,10 +326,10 @@ See the [@json-render/react-email API reference](/docs/api/react-email) for the
 `@json-render/remotion` takes a different approach. Instead of `defineRegistry`, it uses a plain component registry with built-in standard components for video production:
 
 ```tsx
-import { Renderer, standardComponents } from '@json-render/remotion';
+import { Renderer, standardComponents } from "@json-render/remotion";
 
 // Use the standard components directly
-<Renderer spec={timelineSpec} components={standardComponents} />
+<Renderer spec={timelineSpec} components={standardComponents} />;
 
 // Or extend with your own
 const components = {

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

@@ -62,6 +62,15 @@ All renderers share the same workflow:
       </td>
       <td>Native mobile views</td>
     </tr>
+    <tr>
+      <td>TanStack Start</td>
+      <td>
+        <code>@json-render/tanstack-start</code>
+      </td>
+      <td>
+        Full React applications with routes, layouts, SSR, and head metadata
+      </td>
+    </tr>
     <tr>
       <td>Image</td>
       <td>
@@ -213,6 +222,32 @@ const { registry } = defineRegistry(catalog, { components: {} });
 
 See the [@json-render/react-native API reference](/docs/api/react-native) for details.
 
+## TanStack Start
+
+Define complete TanStack Start applications with route specs, reusable layouts,
+loader-backed state, head metadata, and prerender paths. The integration uses
+the React renderer for each page and TanStack Router for navigation.
+
+```tsx
+import { createFileRoute, notFound } from "@tanstack/react-router";
+import { PageRenderer } from "@json-render/tanstack-start";
+import { createStartApp } from "@json-render/tanstack-start/server";
+
+const { getPageData, getHead } = createStartApp({ spec });
+
+export const Route = createFileRoute("/$")({
+  loader: async ({ location }) => {
+    const data = await getPageData({ pathname: location.pathname });
+    if (!data) throw notFound();
+    return data;
+  },
+  head: ({ match }) => getHead({ pathname: match.pathname }),
+  component: () => <PageRenderer {...Route.useLoaderData()} />,
+});
+```
+
+See the [@json-render/tanstack-start API reference](/docs/api/tanstack-start) for details.
+
 ## Image
 
 Generate SVG and PNG images from JSON specs using Satori. Ideal for OG images, social cards, and banners.

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

@@ -10,6 +10,7 @@ json-render ships with skills that teach AI coding agents how to use each packag
 
 - **core** — Core schemas, catalogs, and AI prompt generation.
 - **react** — React renderer that turns JSON specs into React component trees.
+- **tanstack-start** — Full TanStack Start applications with routes, layouts, SSR loaders, and head metadata.
 - **react-pdf** — PDF renderer using `@react-pdf/renderer`.
 - **react-email** — Email renderer that produces HTML or plain-text emails.
 - **react-native** — React Native renderer for native mobile UIs.
@@ -31,6 +32,7 @@ json-render ships with skills that teach AI coding agents how to use each packag
 ```bash
 npx skills add vercel-labs/json-render --skill core
 npx skills add vercel-labs/json-render --skill react
+npx skills add vercel-labs/json-render --skill tanstack-start
 npx skills add vercel-labs/json-render --skill react-pdf
 npx skills add vercel-labs/json-render --skill react-email
 npx skills add vercel-labs/json-render --skill react-native
@@ -58,6 +60,10 @@ The foundational skill. Teaches agents how to define catalogs, create schemas, b
 
 Teaches agents how to render JSON specs as React component trees using `JsonRender`, `JsonRenderClient`, and `useJsonRender`. Covers custom component registries, client-side interactivity, state management, and streaming integration.
 
+## tanstack-start
+
+Teaches agents how to build JSON-defined TanStack Start applications with splat routes, reusable layouts, SSR-safe loaders, head metadata, prerender paths, and client navigation.
+
 ## react-pdf
 
 Teaches agents how to generate PDFs from JSON specs using `@react-pdf/renderer`. Covers the PDF-specific component registry, page layout, and styling.

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

@@ -1,5 +1,5 @@
-import { pageMetadata } from "@/lib/page-metadata"
-export const metadata = pageMetadata("docs/specs")
+import { pageMetadata } from "@/lib/page-metadata";
+export const metadata = pageMetadata("docs/specs");
 
 # Specs
 
@@ -60,7 +60,10 @@ A more complex spec with multiple nested elements:
     },
     "avatar-1": {
       "type": "Avatar",
-      "props": { "src": { "$state": "/user/avatar" }, "alt": { "$state": "/user/name" } },
+      "props": {
+        "src": { "$state": "/user/avatar" },
+        "alt": { "$state": "/user/name" }
+      },
       "children": []
     },
     "stack-1": {
@@ -102,7 +105,10 @@ A high-level spec using semantic blocks for page layouts:
     },
     "header": {
       "type": "Header",
-      "props": { "logo": "/logo.svg", "navItems": ["Products", "Pricing", "Docs"] },
+      "props": {
+        "logo": "/logo.svg",
+        "navItems": ["Products", "Pricing", "Docs"]
+      },
       "children": []
     },
     "hero": {
@@ -122,22 +128,37 @@ A high-level spec using semantic blocks for page layouts:
     },
     "feature-1": {
       "type": "Feature",
-      "props": { "icon": "zap", "title": "Fast", "description": "Render UIs in milliseconds" },
+      "props": {
+        "icon": "zap",
+        "title": "Fast",
+        "description": "Render UIs in milliseconds"
+      },
       "children": []
     },
     "feature-2": {
       "type": "Feature",
-      "props": { "icon": "shield", "title": "Secure", "description": "Validate all specs against your catalog" },
+      "props": {
+        "icon": "shield",
+        "title": "Secure",
+        "description": "Validate all specs against your catalog"
+      },
       "children": []
     },
     "feature-3": {
       "type": "Feature",
-      "props": { "icon": "sparkles", "title": "AI-Ready", "description": "Generate prompts from your catalog" },
+      "props": {
+        "icon": "sparkles",
+        "title": "AI-Ready",
+        "description": "Generate prompts from your catalog"
+      },
       "children": []
     },
     "footer": {
       "type": "Footer",
-      "props": { "copyright": "2025 Acme Inc", "links": ["Privacy", "Terms", "Contact"] },
+      "props": {
+        "copyright": "2025 Acme Inc",
+        "links": ["Privacy", "Terms", "Contact"]
+      },
       "children": []
     }
   }
@@ -174,13 +195,18 @@ Each element in the map has a consistent shape:
 {
   "type": "ComponentName",
   "props": { "label": "Hello" },
-  "children": ["child-1", "child-2"]
+  "children": ["child-1", "child-2"],
+  "slots": {
+    "header": ["heading-1"],
+    "footer": ["actions-1"]
+  }
 }
 ```
 
 - `type` — Component type from your catalog
 - `props` — Component properties
 - `children` — Array of child element keys
+- `slots`: Optional map of named slots to child element keys. Use `children` for the default slot. Named slot rendering is supported by `@json-render/react` and `@json-render/vue`.
 
 ### Dynamic Data
 
@@ -225,12 +251,12 @@ Control when elements appear using the `visible` property:
 Use `validateSpec` from `@json-render/core` to check a spec for structural issues:
 
 ```typescript
-import { validateSpec } from '@json-render/core';
+import { validateSpec } from "@json-render/core";
 
 const result = validateSpec(spec);
 
 if (!result.valid) {
-  console.error('Invalid spec:', result.issues);
+  console.error("Invalid spec:", result.issues);
 }
 ```
 
@@ -239,8 +265,12 @@ if (!result.valid) {
 With `@json-render/react`, wrap the `Renderer` in providers to supply state and visibility:
 
 ```tsx
-import { Renderer, StateProvider, VisibilityProvider } from '@json-render/react';
-import { registry } from './registry';
+import {
+  Renderer,
+  StateProvider,
+  VisibilityProvider,
+} from "@json-render/react";
+import { registry } from "./registry";
 
 function MyApp({ spec, initialState }) {
   return (
@@ -260,20 +290,14 @@ See the [@json-render/react API reference](/docs/api/react) for full provider an
 With `@json-render/react`, use the `useUIStream` hook to stream specs incrementally:
 
 ```tsx
-import { useUIStream } from '@json-render/react';
+import { useUIStream } from "@json-render/react";
 
 function GenerativeUI() {
   const { spec, isStreaming } = useUIStream({
-    api: '/api/generate',
+    api: "/api/generate",
   });
 
-  return (
-    <Renderer
-      spec={spec}
-      registry={registry}
-      loading={isStreaming}
-    />
-  );
+  return <Renderer spec={spec} registry={registry} loading={isStreaming} />;
 }
 ```
 

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

@@ -199,6 +199,24 @@ With comparison:
 
 This shows the divider for every item except the first (index 0).
 
+### Filtered lists — `$item` on the repeat container
+
+Putting an `$item` condition directly on the element that declares `repeat` filters which items render. This is the natural way to build kanban columns, tabbed lists, or status sections from one state array:
+
+```json
+{
+  "type": "Stack",
+  "repeat": { "statePath": "/tasks", "key": "id" },
+  "visible": { "$item": "status", "eq": "todo" },
+  "children": ["task-card"]
+}
+```
+
+One child renders per matching item; non-matching items are skipped. When the condition is an `$and` (or array) that mixes scopes, the `$state` parts gate the container itself (a false gate hides the whole shell) while the `$item`/`$index` parts filter items. A mixed `$or` cannot be split and is applied entirely per item.
+
+Filtered lists are currently implemented by the React renderer; other renderers evaluate the container condition outside the repeat scope.
+
+
 `$item` and `$index` conditions support the same comparison operators as `$state` (`eq`, `neq`, `gt`, `gte`, `lt`, `lte`, `not`).
 
 ## Complex Example

apps/web/app/(main)/layout.tsx

@@ -1,13 +1,16 @@
 import { Header } from "@/components/header";
+import { getStarCount } from "@/lib/github";
 
-export default function MainLayout({
+export default async function MainLayout({
   children,
 }: {
   children: React.ReactNode;
 }) {
+  const stars = await getStarCount();
+
   return (
     <div className="min-h-screen flex flex-col">
-      <Header />
+      <Header stars={stars} />
       <main className="flex-1">{children}</main>
     </div>
   );

apps/web/app/api/docs-chat/route.ts

@@ -16,8 +16,8 @@ const SYSTEM_PROMPT = `You are a helpful documentation assistant for json-render
 
 GitHub repository: https://github.com/vercel-labs/json-render
 Documentation: https://json-render.dev/docs
-npm packages: @json-render/core, @json-render/react, @json-render/ink, @json-render/vue, @json-render/svelte, @json-render/solid, @json-render/shadcn, @json-render/react-three-fiber, @json-render/react-native, @json-render/react-email, @json-render/react-pdf, @json-render/image, @json-render/remotion, @json-render/codegen, @json-render/mcp, @json-render/redux, @json-render/zustand, @json-render/jotai, @json-render/xstate, @json-render/yaml
-Skills: json-render ships AI agent skills that teach coding agents how to use each package. Install with "npx skills add vercel-labs/json-render --skill <name>". Available skills: core, react, ink, react-pdf, react-email, react-native, shadcn, react-three-fiber, image, remotion, vue, svelte, solid, codegen, mcp, redux, zustand, jotai, xstate, yaml. See /docs/skills for details.
+npm packages: @json-render/core, @json-render/react, @json-render/next, @json-render/tanstack-start, @json-render/ink, @json-render/vue, @json-render/svelte, @json-render/solid, @json-render/shadcn, @json-render/shadcn-svelte, @json-render/react-three-fiber, @json-render/react-native, @json-render/react-email, @json-render/react-pdf, @json-render/image, @json-render/remotion, @json-render/directives, @json-render/codegen, @json-render/devtools, @json-render/devtools-react, @json-render/devtools-vue, @json-render/devtools-svelte, @json-render/devtools-solid, @json-render/mcp, @json-render/redux, @json-render/zustand, @json-render/jotai, @json-render/xstate, @json-render/yaml
+Skills: json-render ships AI agent skills that teach coding agents how to use each package. Install with "npx skills add vercel-labs/json-render --skill <name>". Available skills: core, react, next, tanstack-start, ink, react-pdf, react-email, react-native, shadcn, shadcn-svelte, react-three-fiber, image, remotion, vue, svelte, solid, directives, codegen, devtools, mcp, redux, zustand, jotai, xstate, yaml. See /docs/skills for details.
 
 You have access to the full json-render documentation via the bash and readFile tools. The docs are available as markdown files in the /workspace/docs/ directory.
 

apps/web/app/api/generate/route.ts

@@ -17,10 +17,13 @@ const PLAYGROUND_RULES = [
   "NEVER use viewport height classes (min-h-screen, h-screen) - the UI renders inside a fixed-size container.",
   "NEVER use page background colors (bg-gray-50) - the container has its own background.",
   "For forms or small UIs: use Card as root with maxWidth:'sm' or 'md' and centered:true.",
-  "For content-heavy UIs (blogs, dashboards, product listings): use Stack or Grid as root. Use Grid with 2-3 columns for card layouts.",
+  "For content-heavy UIs (blogs, dashboards, product listings): use Stack or Grid as root. Use Grid with 2-3 columns for card layouts. Keep the total UI compact — avoid sprawling multi-section pages. Prefer a single focused Card over a full page layout.",
   "Wrap each repeated item in a Card for visual separation and structure.",
   "Use realistic, professional sample data. Include 3-5 items with varied content. Never leave state arrays empty.",
   'For form inputs (Input, Textarea, Select), always include checks for validation (e.g. required, email, minLength). Always pair checks with a $bindState expression on the value prop (e.g. { "$bindState": "/path" }).',
+  "NEVER use emoji characters. Use the Icon component with Lucide icon names instead. For example, use Icon with name:'MapPin' instead of a pin emoji, Icon with name:'Mail' instead of an envelope emoji, etc.",
+  "For icon+label patterns, use a horizontal Stack with gap:'sm' and align:'center' containing an Icon and a Text.",
+  "For any tabular or list data with consistent columns (items, orders, stats), ALWAYS use the Table component. Never simulate tables with Stacks — the columns won't align.",
 ];
 
 const MAX_PROMPT_LENGTH = 500;

apps/web/components/demo.tsx

@@ -18,65 +18,62 @@ import { PlaygroundRenderer } from "@/lib/render/renderer";
 import { playgroundCatalog } from "@/lib/render/catalog";
 import { buildCatalogDisplayData } from "@/lib/render/catalog-display";
 
-const SIMULATION_PROMPT = "Create a contact form with name, email, and message";
+const SIMULATION_PROMPT = "Show a team performance dashboard";
 
 interface SimulationStage {
   tree: Spec;
   stream: string;
 }
 
-// Shared state & element definitions for the progressive simulation stages.
-const FORM_STATE = { form: { name: "", email: "", message: "" } };
+const DASH_STATE = {
+  chartData: [
+    { label: "Mon", value: 12 },
+    { label: "Tue", value: 28 },
+    { label: "Wed", value: 19 },
+    { label: "Thu", value: 34 },
+    { label: "Fri", value: 45 },
+    { label: "Sat", value: 38 },
+    { label: "Sun", value: 52 },
+  ],
+};
 
-const NAME_INPUT = {
-  type: "Input",
+const METRIC_REVENUE = {
+  type: "Metric",
   props: {
-    label: "Name",
-    name: "name",
-    statePath: "/form/name",
-    checks: [{ type: "required", message: "Name is required" }],
+    label: "Weekly Revenue",
+    value: "12,400",
+    prefix: "$",
+    change: "+18%",
+    changeType: "positive",
   },
 } as const;
 
-const EMAIL_INPUT = {
-  type: "Input",
-  props: {
-    label: "Email",
-    name: "email",
-    type: "email",
-    statePath: "/form/email",
-    checks: [
-      { type: "required", message: "Email is required" },
-      { type: "email", message: "Please enter a valid email" },
-    ],
-  },
+const CHART = {
+  type: "LineGraph",
+  props: { data: { $state: "/chartData" } },
 } as const;
 
-const MESSAGE_INPUT = {
-  type: "Textarea",
-  props: {
-    label: "Message",
-    name: "message",
-    statePath: "/form/message",
-    checks: [{ type: "required", message: "Message is required" }],
-  },
+const SEP = { type: "Separator", props: {} } as const;
+
+const PROGRESS_DEALS = {
+  type: "Progress",
+  props: { value: 72, label: "Deals Closed -- 72%" },
 } as const;
 
-const SUBMIT_BUTTON = {
-  type: "Button",
-  props: { label: "Send Message", variant: "primary" },
-  on: { press: { action: "formSubmit" } },
+const PROGRESS_RETENTION = {
+  type: "Progress",
+  props: { value: 91, label: "Retention -- 91%" },
 } as const;
 
 const SIMULATION_STAGES: SimulationStage[] = [
   {
     tree: {
       root: "card",
-      state: FORM_STATE,
+      state: DASH_STATE,
       elements: {
         card: {
           type: "Card",
-          props: { title: "Contact Us", maxWidth: "md" },
+          props: { title: "Team Performance", maxWidth: "sm", centered: true },
           children: [],
         },
       },
@@ -86,72 +83,74 @@ const SIMULATION_STAGES: SimulationStage[] = [
   {
     tree: {
       root: "card",
-      state: FORM_STATE,
+      state: DASH_STATE,
       elements: {
         card: {
           type: "Card",
-          props: { title: "Contact Us", maxWidth: "md" },
-          children: ["name"],
+          props: { title: "Team Performance", maxWidth: "sm", centered: true },
+          children: ["m1"],
         },
-        name: NAME_INPUT,
+        m1: METRIC_REVENUE,
       },
     },
     stream:
-      '{"op":"add","path":"/elements/name","value":{"type":"Input","props":{"label":"Name","name":"name","statePath":"/form/name","checks":[{"type":"required","message":"Name is required"}]}}}',
+      '{"op":"add","path":"/elements/m1","value":{"type":"Metric","props":{"label":"Weekly Revenue","value":"12,400","prefix":"$","change":"+18%","changeType":"positive"}}}',
   },
   {
     tree: {
       root: "card",
-      state: FORM_STATE,
+      state: DASH_STATE,
       elements: {
         card: {
           type: "Card",
-          props: { title: "Contact Us", maxWidth: "md" },
-          children: ["name", "email"],
+          props: { title: "Team Performance", maxWidth: "sm", centered: true },
+          children: ["m1", "chart"],
         },
-        name: NAME_INPUT,
-        email: EMAIL_INPUT,
+        m1: METRIC_REVENUE,
+        chart: CHART,
       },
     },
     stream:
-      '{"op":"add","path":"/elements/email","value":{"type":"Input","props":{"label":"Email","name":"email","type":"email","statePath":"/form/email","checks":[{"type":"required","message":"Email is required"},{"type":"email","message":"Please enter a valid email"}]}}}',
+      '{"op":"add","path":"/elements/chart","value":{"type":"LineGraph","props":{"data":{"$state":"/chartData"}}}}',
   },
   {
     tree: {
       root: "card",
-      state: FORM_STATE,
+      state: DASH_STATE,
       elements: {
         card: {
           type: "Card",
-          props: { title: "Contact Us", maxWidth: "md" },
-          children: ["name", "email", "message"],
+          props: { title: "Team Performance", maxWidth: "sm", centered: true },
+          children: ["m1", "chart", "sep", "p1"],
         },
-        name: NAME_INPUT,
-        email: EMAIL_INPUT,
-        message: MESSAGE_INPUT,
+        m1: METRIC_REVENUE,
+        chart: CHART,
+        sep: SEP,
+        p1: PROGRESS_DEALS,
       },
     },
     stream:
-      '{"op":"add","path":"/elements/message","value":{"type":"Textarea","props":{"label":"Message","name":"message","statePath":"/form/message","checks":[{"type":"required","message":"Message is required"}]}}}',
+      '{"op":"add","path":"/elements/p1","value":{"type":"Progress","props":{"value":72,"label":"Deals Closed -- 72%"}}}',
   },
   {
     tree: {
       root: "card",
-      state: FORM_STATE,
+      state: DASH_STATE,
       elements: {
         card: {
           type: "Card",
-          props: { title: "Contact Us", maxWidth: "md" },
-          children: ["name", "email", "message", "submit"],
+          props: { title: "Team Performance", maxWidth: "sm", centered: true },
+          children: ["m1", "chart", "sep", "p1", "p2"],
         },
-        name: NAME_INPUT,
-        email: EMAIL_INPUT,
-        message: MESSAGE_INPUT,
-        submit: SUBMIT_BUTTON,
+        m1: METRIC_REVENUE,
+        chart: CHART,
+        sep: SEP,
+        p1: PROGRESS_DEALS,
+        p2: PROGRESS_RETENTION,
       },
     },
     stream:
-      '{"op":"add","path":"/elements/submit","value":{"type":"Button","props":{"label":"Send Message","variant":"primary"},"on":{"press":{"action":"formSubmit"}}}}',
+      '{"op":"add","path":"/elements/p2","value":{"type":"Progress","props":{"value":91,"label":"Retention -- 91%"}}}',
   },
 ];
 
@@ -196,6 +195,15 @@ function specToNested(spec: Spec): Record<string, unknown> {
       node.children = el.children.map(resolve);
     }
 
+    if (el.slots && Object.keys(el.slots).length > 0) {
+      node.slots = Object.fromEntries(
+        Object.entries(el.slots).map(([slotName, childKeys]) => [
+          slotName,
+          childKeys.map(resolve),
+        ]),
+      );
+    }
+
     return node;
   }
 
@@ -211,10 +219,10 @@ function specToNested(spec: Spec): Record<string, unknown> {
 }
 
 const EXAMPLE_PROMPTS = [
-  "Create a login form with email and password",
-  "Build a feedback form with rating stars",
-  "Design a contact card with avatar",
-  "Make a settings panel with toggles",
+  "Recipe card with rating and ingredients",
+  "Order receipt with item list and total",
+  "Team member profile card",
+  "Notification inbox with alerts",
 ];
 
 export function Demo({
@@ -394,21 +402,45 @@ export function Demo({
 
       const propsStr = serializeProps(propsObj);
       const hasChildren = element.children && element.children.length > 0;
+      const hasSlots = element.slots && Object.keys(element.slots).length > 0;
 
-      if (!hasChildren) {
+      if (!hasChildren && !hasSlots) {
         return propsStr
           ? `${spaces}<${componentName} ${propsStr} />`
           : `${spaces}<${componentName} />`;
       }
 
       const lines: string[] = [];
-      lines.push(
-        propsStr
-          ? `${spaces}<${componentName} ${propsStr}>`
-          : `${spaces}<${componentName}>`,
-      );
+      if (hasSlots) {
+        lines.push(`${spaces}<${componentName}`);
+        if (propsStr) {
+          lines.push(`${spaces}  ${propsStr}`);
+        }
+        for (const [slotName, childKeys] of Object.entries(element.slots!)) {
+          const slotChildren = childKeys
+            .map((childKey) => generateJSX(childKey, indent + 2))
+            .filter(Boolean);
+          if (slotChildren.length === 0) continue;
+          lines.push(`${spaces}  ${slotName}={`);
+          if (slotChildren.length > 1) {
+            lines.push(`${spaces}    <>`);
+          }
+          lines.push(...slotChildren);
+          if (slotChildren.length > 1) {
+            lines.push(`${spaces}    </>`);
+          }
+          lines.push(`${spaces}  }`);
+        }
+        lines.push(`${spaces}>`);
+      } else {
+        lines.push(
+          propsStr
+            ? `${spaces}<${componentName} ${propsStr}>`
+            : `${spaces}<${componentName}>`,
+        );
+      }
 
-      for (const childKey of element.children!) {
+      for (const childKey of element.children ?? []) {
         lines.push(generateJSX(childKey, indent + 1));
       }
 
@@ -1117,7 +1149,7 @@ Open [http://localhost:3000](http://localhost:3000) to view.
             ))}
           </div>
           <div
-            className={`border border-border rounded bg-background font-mono text-xs text-left grid relative group ${fullscreen ? "flex-1 min-h-0" : "h-[28rem]"}`}
+            className={`border border-border rounded bg-background font-mono text-xs text-left grid relative group ${fullscreen ? "flex-1 min-h-0" : "h-[36rem]"}`}
           >
             {activeTab !== "catalog" && (
               <div className="absolute top-2 right-2 z-10">
@@ -1357,7 +1389,7 @@ Open [http://localhost:3000](http://localhost:3000) to view.
             </div>
           </div>
           <div
-            className={`border border-border rounded bg-background grid relative group ${fullscreen ? "flex-1 min-h-0" : "h-[28rem]"}`}
+            className={`border border-border rounded bg-background grid relative group ${fullscreen ? "flex-1 min-h-0" : "h-[36rem]"}`}
           >
             {renderView === "static" && (
               <div className="absolute top-2 right-2 z-10">

apps/web/components/header.tsx

@@ -19,7 +19,13 @@ const navLinks = [
   { href: "/docs", label: "Docs" },
 ];
 
-function GitHubLink({ className }: { className?: string }) {
+function GitHubLink({
+  className,
+  stars,
+}: {
+  className?: string;
+  stars?: string;
+}) {
   return (
     <a
       href="https://github.com/vercel-labs/json-render"
@@ -38,12 +44,12 @@ function GitHubLink({ className }: { className?: string }) {
       >
         <path d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0016 8c0-4.42-3.58-8-8-8z" />
       </svg>
-      <span>12k</span>
+      {stars && <span>{stars}</span>}
     </a>
   );
 }
 
-export function Header() {
+export function Header({ stars }: { stars?: string }) {
   const pathname = usePathname();
   const [mobileOpen, setMobileOpen] = useState(false);
 
@@ -122,14 +128,14 @@ export function Header() {
             </Link>
           ))}
           <Search />
-          <GitHubLink />
+          <GitHubLink stars={stars} />
           <ThemeToggle />
         </nav>
 
         {/* Mobile nav */}
         <div className="flex sm:hidden items-center gap-3">
           <Search />
-          <GitHubLink />
+          <GitHubLink stars={stars} />
           <Sheet open={mobileOpen} onOpenChange={setMobileOpen}>
             <SheetTrigger
               className="flex items-center justify-center"

apps/web/components/playground.tsx

@@ -152,6 +152,15 @@ function specToNested(spec: Spec): Record<string, unknown> {
       node.children = el.children.map(resolve);
     }
 
+    if (el.slots && Object.keys(el.slots).length > 0) {
+      node.slots = Object.fromEntries(
+        Object.entries(el.slots).map(([slotName, childKeys]) => [
+          slotName,
+          childKeys.map(resolve),
+        ]),
+      );
+    }
+
     return node;
   }
 
@@ -373,21 +382,45 @@ export function Playground() {
 
       const propsStr = serializeProps(propsObj);
       const hasChildren = element.children && element.children.length > 0;
+      const hasSlots = element.slots && Object.keys(element.slots).length > 0;
 
-      if (!hasChildren) {
+      if (!hasChildren && !hasSlots) {
         return propsStr
           ? `${spaces}<${componentName} ${propsStr} />`
           : `${spaces}<${componentName} />`;
       }
 
       const lines: string[] = [];
-      lines.push(
-        propsStr
-          ? `${spaces}<${componentName} ${propsStr}>`
-          : `${spaces}<${componentName}>`,
-      );
+      if (hasSlots) {
+        lines.push(`${spaces}<${componentName}`);
+        if (propsStr) {
+          lines.push(`${spaces}  ${propsStr}`);
+        }
+        for (const [slotName, childKeys] of Object.entries(element.slots!)) {
+          const slotChildren = childKeys
+            .map((childKey) => generateJSX(childKey, indent + 2))
+            .filter(Boolean);
+          if (slotChildren.length === 0) continue;
+          lines.push(`${spaces}  ${slotName}={`);
+          if (slotChildren.length > 1) {
+            lines.push(`${spaces}    <>`);
+          }
+          lines.push(...slotChildren);
+          if (slotChildren.length > 1) {
+            lines.push(`${spaces}    </>`);
+          }
+          lines.push(`${spaces}  }`);
+        }
+        lines.push(`${spaces}>`);
+      } else {
+        lines.push(
+          propsStr
+            ? `${spaces}<${componentName} ${propsStr}>`
+            : `${spaces}<${componentName}>`,
+        );
+      }
 
-      for (const childKey of element.children!) {
+      for (const childKey of element.children ?? []) {
         lines.push(generateJSX(childKey, indent + 1));
       }
 

apps/web/lib/docs-navigation.ts

@@ -32,6 +32,7 @@ export const docsNavigation: NavSection[] = [
       { title: "Visibility", href: "/docs/visibility" },
       { title: "Watchers", href: "/docs/watchers" },
       { title: "Validation", href: "/docs/validation" },
+      { title: "Directives", href: "/docs/directives" },
     ],
   },
   {
@@ -52,6 +53,7 @@ export const docsNavigation: NavSection[] = [
     items: [
       { title: "Custom Schema", href: "/docs/custom-schema" },
       { title: "Code Export", href: "/docs/code-export" },
+      { title: "Devtools", href: "/docs/devtools" },
     ],
   },
   {
@@ -69,9 +71,15 @@ export const docsNavigation: NavSection[] = [
     items: [
       { title: "@json-render/core", href: "/docs/api/core" },
       { title: "@json-render/react", href: "/docs/api/react" },
+      { title: "@json-render/next", href: "/docs/api/next" },
+      {
+        title: "@json-render/tanstack-start",
+        href: "/docs/api/tanstack-start",
+      },
       { title: "@json-render/react-pdf", href: "/docs/api/react-pdf" },
       { title: "@json-render/react-email", href: "/docs/api/react-email" },
       { title: "@json-render/shadcn", href: "/docs/api/shadcn" },
+      { title: "@json-render/shadcn-svelte", href: "/docs/api/shadcn-svelte" },
       { title: "@json-render/react-native", href: "/docs/api/react-native" },
       { title: "@json-render/image", href: "/docs/api/image" },
       { title: "@json-render/remotion", href: "/docs/api/remotion" },
@@ -83,7 +91,22 @@ export const docsNavigation: NavSection[] = [
         title: "@json-render/react-three-fiber",
         href: "/docs/api/react-three-fiber",
       },
+      { title: "@json-render/directives", href: "/docs/api/directives" },
       { title: "@json-render/codegen", href: "/docs/api/codegen" },
+      { title: "@json-render/devtools", href: "/docs/api/devtools" },
+      {
+        title: "@json-render/devtools-react",
+        href: "/docs/api/devtools-react",
+      },
+      { title: "@json-render/devtools-vue", href: "/docs/api/devtools-vue" },
+      {
+        title: "@json-render/devtools-svelte",
+        href: "/docs/api/devtools-svelte",
+      },
+      {
+        title: "@json-render/devtools-solid",
+        href: "/docs/api/devtools-solid",
+      },
       { title: "@json-render/mcp", href: "/docs/api/mcp" },
       { title: "@json-render/redux", href: "/docs/api/redux" },
       { title: "@json-render/zustand", href: "/docs/api/zustand" },

apps/web/lib/examples.ts

@@ -108,6 +108,22 @@ export const examples: Example[] = [
     githubPath: "examples/react-three-fiber",
     demoUrl: "https://react-three-fiber-demo.json-render.dev",
   },
+  {
+    slug: "gsplat",
+    title: "Gaussian Splatting (experimental)",
+    description:
+      "Experimental standalone gaussian splat viewer using gsplat.js — no Three.js dependency.",
+    tags: ["React", "3D", "Next.js"],
+    githubPath: "examples/gsplat",
+  },
+  {
+    slug: "react-three-fiber-gsplat",
+    title: "R3F + Gaussian Splatting",
+    description:
+      "Gaussian splats composed with 3D primitives and lights in React Three Fiber scenes.",
+    tags: ["React", "3D", "Next.js"],
+    githubPath: "examples/react-three-fiber-gsplat",
+  },
   {
     slug: "react-native",
     title: "React Native",

apps/web/lib/github.ts

@@ -0,0 +1,20 @@
+const REPO = "vercel-labs/json-render";
+const REVALIDATE = 86400;
+
+export async function getStarCount(): Promise<string> {
+  try {
+    const res = await fetch(`https://api.github.com/repos/${REPO}`, {
+      headers: { Accept: "application/vnd.github.v3+json" },
+      next: { revalidate: REVALIDATE },
+    });
+    if (!res.ok) return "";
+    const data = await res.json();
+    const count = data.stargazers_count;
+    if (typeof count !== "number") return "";
+    if (count >= 1000)
+      return `${(count / 1000).toFixed(count >= 10000 ? 0 : 1)}k`;
+    return String(count);
+  } catch {
+    return "";
+  }
+}

apps/web/lib/page-titles.ts

@@ -31,6 +31,7 @@ export const PAGE_TITLES: Record<string, string> = {
   "docs/generation-modes": "Generation Modes",
   "docs/code-export": "Code Export",
   "docs/custom-schema": "Custom Schema & Renderer",
+  "docs/devtools": "Devtools",
   "docs/ai-sdk": "AI SDK Integration",
   "docs/adaptive-cards": "Adaptive Cards Integration",
   "docs/openapi": "OpenAPI Integration",
@@ -39,20 +40,30 @@ export const PAGE_TITLES: Record<string, string> = {
   "docs/migration": "Migration Guide",
   "docs/changelog": "Changelog",
   "docs/skills": "Skills",
+  "docs/directives": "Directives",
 
   // API references
   "docs/api/core": "@json-render/core API",
   "docs/api/react": "@json-render/react API",
+  "docs/api/next": "@json-render/next API",
+  "docs/api/tanstack-start": "@json-render/tanstack-start API",
   "docs/api/vue": "@json-render/vue API",
   "docs/api/solid": "@json-render/solid API",
   "docs/api/react-pdf": "@json-render/react-pdf API",
   "docs/api/react-email": "@json-render/react-email API",
   "docs/api/react-native": "@json-render/react-native API",
   "docs/api/svelte": "@json-render/svelte API",
+  "docs/api/directives": "@json-render/directives API",
   "docs/api/codegen": "@json-render/codegen API",
+  "docs/api/devtools": "@json-render/devtools API",
+  "docs/api/devtools-react": "@json-render/devtools-react API",
+  "docs/api/devtools-vue": "@json-render/devtools-vue API",
+  "docs/api/devtools-svelte": "@json-render/devtools-svelte API",
+  "docs/api/devtools-solid": "@json-render/devtools-solid API",
   "docs/api/image": "@json-render/image API",
   "docs/api/remotion": "@json-render/remotion API",
   "docs/api/shadcn": "@json-render/shadcn API",
+  "docs/api/shadcn-svelte": "@json-render/shadcn-svelte API",
   "docs/api/mcp": "@json-render/mcp API",
   "docs/api/redux": "@json-render/redux API",
   "docs/api/zustand": "@json-render/zustand API",

apps/web/lib/render/catalog.ts

@@ -165,7 +165,8 @@ export const playgroundCatalog = defineCatalog(schema, {
           .enum(["body", "caption", "muted", "lead", "code"])
           .nullable(),
       }),
-      description: "Paragraph text",
+      description:
+        'Paragraph text. In repeat scopes, use { "$template": "${field1} ${field2}" } to interpolate item fields.',
       example: { text: "Hello, world!" },
     },
 
@@ -178,6 +179,18 @@ export const playgroundCatalog = defineCatalog(schema, {
       description: "Placeholder image (displays alt text in a styled box)",
     },
 
+    Icon: {
+      props: z.object({
+        name: z.string(),
+        size: z.enum(["sm", "md", "lg"]).nullable(),
+        color: z
+          .enum(["default", "muted", "primary", "success", "warning", "danger"])
+          .nullable(),
+      }),
+      description:
+        "Lucide icon by name. PascalCase: MapPin, Mail, Globe, Calendar, Star, Heart, Check, X, ArrowRight, Phone, Building, Clock, Shield, Zap, Users, Eye, Download, Upload, Search, Filter, Settings, Bell, ChevronRight, ExternalLink, Info, AlertTriangle, CheckCircle, XCircle. Use in horizontal Stacks with Text for icon+label patterns. Never use emoji — always use Icon.",
+    },
+
     Avatar: {
       props: z.object({
         src: z.string().nullable(),
@@ -259,8 +272,32 @@ export const playgroundCatalog = defineCatalog(schema, {
         value: z.number(),
         max: z.number().nullable(),
         label: z.string().nullable(),
+        interactive: z.boolean().nullable(),
       }),
-      description: "Star rating display",
+      events: ["change"],
+      description:
+        "Interactive star rating. Use { $bindState } on value for binding. Set interactive: false for read-only display.",
+      example: { value: 4, max: 5, label: "Rating" },
+    },
+
+    Metric: {
+      props: z.object({
+        label: z.string(),
+        value: z.string(),
+        change: z.string().nullable(),
+        changeType: z.enum(["positive", "negative", "neutral"]).nullable(),
+        prefix: z.string().nullable(),
+        suffix: z.string().nullable(),
+      }),
+      description:
+        "Key metric / stat display. Shows a large value with label and optional change indicator. Use for dashboard KPIs.",
+      example: {
+        label: "Total Revenue",
+        value: "125,000",
+        prefix: "$",
+        change: "+12.5%",
+        changeType: "positive",
+      },
     },
 
     // ── Charts ──────────────────────────────────────────────────────────
@@ -411,11 +448,14 @@ export const playgroundCatalog = defineCatalog(schema, {
     Button: {
       props: z.object({
         label: z.string(),
-        variant: z.enum(["primary", "secondary", "danger"]).nullable(),
+        variant: z
+          .enum(["primary", "secondary", "outline", "danger"])
+          .nullable(),
         disabled: z.boolean().nullable(),
       }),
       events: ["press"],
-      description: "Clickable button. Bind on.press for handler.",
+      description:
+        "Clickable button. primary = solid fill, outline = bordered/transparent, secondary = muted fill. Bind on.press for handler.",
       example: { label: "Submit", variant: "primary" },
     },
 

apps/web/lib/render/registry.tsx

@@ -105,6 +105,7 @@ import {
   TooltipProvider,
   TooltipTrigger,
 } from "@/components/ui/tooltip";
+import { icons as lucideIcons } from "lucide-react";
 
 // =============================================================================
 // Registry — components + actions, types inferred from catalog
@@ -127,23 +128,25 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
 
       return (
         <div
-          className={`border border-border rounded-lg p-4 bg-card text-card-foreground overflow-hidden ${maxWidthClass} ${centeredClass}`}
+          className={`border border-border rounded-xl p-5 bg-card text-card-foreground shadow-sm overflow-hidden h-full flex flex-col ${maxWidthClass} ${centeredClass}`}
         >
           {(props.title || props.description) && (
             <div className="mb-4">
               {props.title && (
-                <h3 className="font-semibold text-lg text-left">
+                <h3 className="font-semibold text-lg tracking-tight">
                   {props.title}
                 </h3>
               )}
               {props.description && (
-                <p className="text-sm text-muted-foreground mt-1 text-left">
+                <p className="text-sm text-muted-foreground mt-1">
                   {props.description}
                 </p>
               )}
             </div>
           )}
-          <div className="space-y-3">{children}</div>
+          <div className="flex-1 flex flex-col gap-4 [&>:last-child]:mt-auto">
+            {children}
+          </div>
         </div>
       );
     },
@@ -160,14 +163,31 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
               : props.gap === "none"
                 ? "gap-0"
                 : "gap-3";
-      const alignClass =
-        props.align === "center"
-          ? "items-center"
-          : props.align === "end"
-            ? "items-end"
-            : props.align === "stretch"
-              ? "items-stretch"
-              : "items-start";
+
+      let alignClass: string;
+      if (isHorizontal) {
+        alignClass =
+          props.align === "center"
+            ? "items-center"
+            : props.align === "end"
+              ? "items-end"
+              : props.align === "stretch"
+                ? "items-stretch"
+                : "items-start";
+      } else {
+        // Vertical: items-center/end lets inline elements (Avatar, Badge, Button)
+        // center/align naturally. Block containers (Grid, Accordion, Table) add
+        // their own w-full to stretch regardless.
+        alignClass =
+          props.align === "center"
+            ? "items-center"
+            : props.align === "end"
+              ? "items-end"
+              : props.align === "start"
+                ? "items-start"
+                : "items-stretch";
+      }
+
       const justifyClass =
         props.justify === "center"
           ? "justify-center"
@@ -181,7 +201,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
 
       return (
         <div
-          className={`flex ${isHorizontal ? "flex-row flex-wrap" : "flex-col"} ${gapClass} ${alignClass} ${justifyClass}`}
+          className={`flex ${isHorizontal ? "flex-row flex-wrap" : "flex-col w-full"} ${gapClass} ${alignClass} ${justifyClass}`}
         >
           {children}
         </div>
@@ -189,7 +209,12 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
     },
 
     Grid: ({ props, children }) => {
-      const n = props.columns ?? 1;
+      const childCount = Array.isArray(children)
+        ? children.length
+        : children
+          ? 1
+          : 0;
+      const n = Math.min(props.columns ?? 1, childCount || 1);
       const cols =
         n >= 6
           ? "grid-cols-6"
@@ -205,13 +230,15 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       const gridGap =
         props.gap === "lg" ? "gap-4" : props.gap === "sm" ? "gap-2" : "gap-3";
 
-      return <div className={`grid ${cols} ${gridGap}`}>{children}</div>;
+      return <div className={`grid w-full ${cols} ${gridGap}`}>{children}</div>;
     },
 
     Separator: ({ props }) => (
       <Separator
         orientation={props.orientation ?? "horizontal"}
-        className={props.orientation === "vertical" ? "h-full mx-2" : "my-3"}
+        className={
+          props.orientation === "vertical" ? "h-full mx-3" : "my-4 opacity-50"
+        }
       />
     ),
 
@@ -383,7 +410,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       });
 
       return (
-        <div className="rounded-md border border-border overflow-hidden">
+        <div className="w-full rounded-md border border-border overflow-hidden">
           <TablePrimitive>
             {props.caption && <TableCaption>{props.caption}</TableCaption>}
             <TableHeader>
@@ -411,20 +438,17 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       const level = props.level ?? "h2";
       const headingClass =
         level === "h1"
-          ? "text-2xl font-bold"
+          ? "text-2xl font-bold tracking-tight"
           : level === "h3"
-            ? "text-base font-semibold"
+            ? "text-base font-semibold tracking-tight"
             : level === "h4"
-              ? "text-sm font-semibold"
-              : "text-lg font-semibold";
+              ? "text-sm font-medium uppercase tracking-wider text-muted-foreground"
+              : "text-xl font-semibold tracking-tight";
 
-      if (level === "h1")
-        return <h1 className={`${headingClass} text-left`}>{props.text}</h1>;
-      if (level === "h3")
-        return <h3 className={`${headingClass} text-left`}>{props.text}</h3>;
-      if (level === "h4")
-        return <h4 className={`${headingClass} text-left`}>{props.text}</h4>;
-      return <h2 className={`${headingClass} text-left`}>{props.text}</h2>;
+      if (level === "h1") return <h1 className={headingClass}>{props.text}</h1>;
+      if (level === "h3") return <h3 className={headingClass}>{props.text}</h3>;
+      if (level === "h4") return <h4 className={headingClass}>{props.text}</h4>;
+      return <h2 className={headingClass}>{props.text}</h2>;
     },
 
     Text: ({ props }) => {
@@ -440,20 +464,59 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
                 : "text-sm";
 
       if (props.variant === "code") {
-        return <code className={`${textClass} text-left`}>{props.text}</code>;
+        return <code className={textClass}>{props.text}</code>;
       }
-      return <p className={`${textClass} text-left`}>{props.text}</p>;
+      return <p className={textClass}>{props.text}</p>;
     },
 
     Image: ({ props }) => (
       <div
-        className="bg-muted border border-border rounded flex items-center justify-center text-xs text-muted-foreground aspect-video"
-        style={{ width: props.width ?? 80, height: props.height ?? 60 }}
+        className="w-full bg-muted/50 border border-dashed border-border rounded-lg flex flex-col items-center justify-center gap-2 text-muted-foreground/60 px-4"
+        style={{
+          maxWidth: props.width ?? undefined,
+          height: props.height ?? 120,
+          minHeight: 80,
+        }}
       >
-        {props.alt || "img"}
+        <svg
+          width="32"
+          height="32"
+          viewBox="0 0 24 24"
+          fill="none"
+          stroke="currentColor"
+          strokeWidth="1.5"
+          strokeLinecap="round"
+          strokeLinejoin="round"
+          className="opacity-50"
+        >
+          <rect width="18" height="18" x="3" y="3" rx="2" ry="2" />
+          <circle cx="9" cy="9" r="2" />
+          <path d="m21 15-3.086-3.086a2 2 0 0 0-2.828 0L6 21" />
+        </svg>
+        {props.alt && <span className="text-xs">{props.alt}</span>}
       </div>
     ),
 
+    Icon: ({ props }) => {
+      const IconComponent = lucideIcons[props.name as keyof typeof lucideIcons];
+      if (!IconComponent) return null;
+      const sizeMap = { sm: 16, md: 20, lg: 24 } as const;
+      const px = sizeMap[props.size ?? "md"] ?? 20;
+      const colorClass =
+        props.color === "muted"
+          ? "text-muted-foreground"
+          : props.color === "primary"
+            ? "text-primary"
+            : props.color === "success"
+              ? "text-green-600 dark:text-green-400"
+              : props.color === "warning"
+                ? "text-yellow-600 dark:text-yellow-400"
+                : props.color === "danger"
+                  ? "text-red-600 dark:text-red-400"
+                  : "";
+      return <IconComponent size={px} className={`shrink-0 ${colorClass}`} />;
+    },
+
     Avatar: ({ props }) => {
       const name = props.name || "?";
       const initials = name
@@ -462,16 +525,16 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
         .join("")
         .slice(0, 2)
         .toUpperCase();
-      const avatarSize =
+      const sizeStyles =
         props.size === "lg"
-          ? "w-12 h-12 text-base"
+          ? { outer: "w-[72px] h-[72px]", text: "text-xl", ring: "ring-[3px]" }
           : props.size === "sm"
-            ? "w-8 h-8 text-xs"
-            : "w-10 h-10 text-sm";
+            ? { outer: "w-8 h-8", text: "text-xs", ring: "ring-2" }
+            : { outer: "w-10 h-10", text: "text-sm", ring: "ring-2" };
 
       return (
         <div
-          className={`${avatarSize} rounded-full bg-muted flex items-center justify-center font-medium`}
+          className={`${sizeStyles.outer} ${sizeStyles.text} rounded-full bg-gradient-to-br from-muted-foreground/20 to-muted flex items-center justify-center font-semibold tracking-wide ${sizeStyles.ring} ring-background shadow-sm`}
         >
           {initials}
         </div>
@@ -491,9 +554,20 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
           : props.variant === "warning"
             ? "bg-yellow-100 text-yellow-800 dark:bg-yellow-900 dark:text-yellow-100"
             : "";
+      const dotColor =
+        props.variant === "success"
+          ? "bg-green-500"
+          : props.variant === "warning"
+            ? "bg-yellow-500"
+            : props.variant === "danger"
+              ? "bg-red-500"
+              : "";
 
       return (
-        <Badge variant={variant} className={customClass}>
+        <Badge variant={variant} className={`${customClass} gap-1.5`}>
+          {dotColor && (
+            <span className={`w-1.5 h-1.5 rounded-full ${dotColor} shrink-0`} />
+          )}
           {props.text}
         </Badge>
       );
@@ -510,8 +584,47 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
               ? "border-blue-200 bg-blue-50 text-blue-900 dark:border-blue-800 dark:bg-blue-950 dark:text-blue-100"
               : "";
 
+      const iconProps = {
+        width: 16,
+        height: 16,
+        viewBox: "0 0 24 24",
+        fill: "none",
+        stroke: "currentColor",
+        strokeWidth: 2,
+        strokeLinecap: "round" as const,
+        strokeLinejoin: "round" as const,
+        className: "shrink-0",
+      };
+
+      const icon =
+        props.type === "success" ? (
+          <svg {...iconProps}>
+            <path d="M22 11.08V12a10 10 0 1 1-5.93-9.14" />
+            <polyline points="22 4 12 14.01 9 11.01" />
+          </svg>
+        ) : props.type === "warning" ? (
+          <svg {...iconProps}>
+            <path d="m21.73 18-8-14a2 2 0 0 0-3.48 0l-8 14A2 2 0 0 0 4 21h16a2 2 0 0 0 1.73-3Z" />
+            <line x1="12" y1="9" x2="12" y2="13" />
+            <line x1="12" y1="17" x2="12.01" y2="17" />
+          </svg>
+        ) : props.type === "error" ? (
+          <svg {...iconProps}>
+            <circle cx="12" cy="12" r="10" />
+            <line x1="15" y1="9" x2="9" y2="15" />
+            <line x1="9" y1="9" x2="15" y2="15" />
+          </svg>
+        ) : (
+          <svg {...iconProps}>
+            <circle cx="12" cy="12" r="10" />
+            <line x1="12" y1="16" x2="12" y2="12" />
+            <line x1="12" y1="8" x2="12.01" y2="8" />
+          </svg>
+        );
+
       return (
         <Alert variant={variant} className={customClass}>
+          {icon}
           <AlertTitle>{props.title}</AlertTitle>
           {props.message && (
             <AlertDescription>{props.message}</AlertDescription>
@@ -523,7 +636,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
     Progress: ({ props }) => {
       const value = Math.min(100, Math.max(0, props.value || 0));
       return (
-        <div className="space-y-2">
+        <div className="w-full space-y-2">
           {props.label && (
             <Label className="text-sm text-muted-foreground">
               {props.label}
@@ -607,9 +720,19 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       </PopoverPrimitive>
     ),
 
-    Rating: ({ props }) => {
-      const ratingValue = props.value || 0;
+    Rating: ({ props, bindings, emit }) => {
+      const [boundValue, setBoundValue] = useBoundProp<number>(
+        props.value as number | undefined,
+        bindings?.value,
+      );
+      const [localValue, setLocalValue] = useState(props.value || 0);
+      const isBound = !!bindings?.value;
+      const ratingValue = isBound ? (boundValue ?? 0) : localValue;
+      const setValue = isBound ? setBoundValue : setLocalValue;
       const maxRating = props.max ?? 5;
+      const interactive = props.interactive !== false;
+      const [hoverIndex, setHoverIndex] = useState(-1);
+
       return (
         <div className="space-y-2">
           {props.label && (
@@ -617,15 +740,78 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
               {props.label}
             </Label>
           )}
-          <div className="flex gap-1">
-            {Array.from({ length: maxRating }).map((_, i) => (
-              <span
-                key={i}
-                className={`text-lg ${i < ratingValue ? "text-yellow-400" : "text-muted"}`}
-              >
-                *
+          <div
+            className="flex gap-0.5"
+            onMouseLeave={() => interactive && setHoverIndex(-1)}
+          >
+            {Array.from({ length: maxRating }).map((_, i) => {
+              const filled =
+                hoverIndex >= 0 ? i <= hoverIndex : i < ratingValue;
+              return (
+                <button
+                  key={i}
+                  type="button"
+                  className={`p-0.5 transition-colors ${interactive ? "cursor-pointer hover:scale-110" : "cursor-default"}`}
+                  onMouseEnter={() => interactive && setHoverIndex(i)}
+                  onClick={() => {
+                    if (!interactive) return;
+                    const newVal = i + 1 === ratingValue ? 0 : i + 1;
+                    setValue(newVal);
+                    emit("change");
+                  }}
+                >
+                  <svg
+                    width="20"
+                    height="20"
+                    viewBox="0 0 24 24"
+                    fill={filled ? "currentColor" : "none"}
+                    stroke="currentColor"
+                    strokeWidth="1.5"
+                    strokeLinecap="round"
+                    strokeLinejoin="round"
+                    className={
+                      filled ? "text-yellow-400" : "text-muted-foreground/40"
+                    }
+                  >
+                    <polygon points="12 2 15.09 8.26 22 9.27 17 14.14 18.18 21.02 12 17.77 5.82 21.02 7 14.14 2 9.27 8.91 8.26 12 2" />
+                  </svg>
+                </button>
+              );
+            })}
+          </div>
+        </div>
+      );
+    },
+
+    Metric: ({ props }) => {
+      const changeColor =
+        props.changeType === "positive"
+          ? "text-green-600 dark:text-green-400"
+          : props.changeType === "negative"
+            ? "text-red-600 dark:text-red-400"
+            : "text-muted-foreground";
+      const changeIcon =
+        props.changeType === "positive"
+          ? "\u2191"
+          : props.changeType === "negative"
+            ? "\u2193"
+            : "";
+
+      return (
+        <div className="space-y-1">
+          <div className="text-sm text-muted-foreground">{props.label}</div>
+          <div className="flex items-baseline gap-1.5">
+            <span className="text-2xl font-semibold tracking-tight tabular-nums">
+              {props.prefix}
+              {props.value}
+              {props.suffix}
+            </span>
+            {props.change && (
+              <span className={`text-sm font-medium ${changeColor}`}>
+                {changeIcon}
+                {props.change}
               </span>
-            ))}
+            )}
           </div>
         </div>
       );
@@ -636,26 +822,39 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
     BarGraph: ({ props }) => {
       const data = props.data || [];
       const maxValue = Math.max(...data.map((d) => d.value), 1);
+      const barColors = [
+        "bg-primary",
+        "bg-primary/80",
+        "bg-primary/60",
+        "bg-primary/70",
+        "bg-primary/90",
+        "bg-primary/50",
+      ];
 
       return (
-        <div className="space-y-2">
+        <div className="space-y-3">
           {props.title && (
-            <div className="text-sm font-medium text-left">{props.title}</div>
+            <div className="text-sm font-medium">{props.title}</div>
           )}
-          <div className="flex gap-2">
+          <div className="flex items-end gap-2" style={{ height: 160 }}>
             {data.map((d, i) => (
-              <div key={i} className="flex-1 flex flex-col items-center gap-1">
-                <div className="text-xs text-muted-foreground">{d.value}</div>
-                <div className="w-full h-24 flex items-end">
+              <div
+                key={i}
+                className="flex-1 flex flex-col items-center gap-1.5 h-full justify-end group"
+              >
+                <div className="text-[11px] font-medium text-muted-foreground tabular-nums">
+                  {d.value}
+                </div>
+                <div className="w-full flex-1 flex items-end">
                   <div
-                    className="w-full bg-primary rounded-t transition-all"
+                    className={`w-full ${barColors[i % barColors.length]} rounded-t-md transition-all group-hover:opacity-80`}
                     style={{
                       height: `${(d.value / maxValue) * 100}%`,
-                      minHeight: 2,
+                      minHeight: 4,
                     }}
                   />
                 </div>
-                <div className="text-xs text-muted-foreground truncate w-full text-center">
+                <div className="text-[11px] text-muted-foreground truncate w-full text-center">
                   {d.label}
                 </div>
               </div>
@@ -672,8 +871,8 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       const range = maxValue - minValue || 1;
 
       const width = 300;
-      const height = 100;
-      const padding = { top: 10, right: 10, bottom: 10, left: 10 };
+      const height = 140;
+      const padding = { top: 12, right: 12, bottom: 12, left: 12 };
       const chartWidth = width - padding.left - padding.right;
       const chartHeight = height - padding.top - padding.bottom;
 
@@ -690,77 +889,107 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
         return { x, y, ...d };
       });
 
-      const pathD =
-        points.length > 0
-          ? `M ${points.map((p) => `${p.x} ${p.y}`).join(" L ")}`
-          : "";
+      // Build smooth cubic bezier curve through points
+      let smoothPath = "";
+      let areaPath = "";
+      if (points.length > 1) {
+        const first = points[0]!;
+        const last = points[points.length - 1]!;
+        smoothPath = `M ${first.x} ${first.y}`;
+        for (let i = 0; i < points.length - 1; i++) {
+          const curr = points[i]!;
+          const next = points[i + 1]!;
+          const cpx = (curr.x + next.x) / 2;
+          smoothPath += ` C ${cpx} ${curr.y}, ${cpx} ${next.y}, ${next.x} ${next.y}`;
+        }
+        const bottomY = height - padding.bottom;
+        areaPath = `${smoothPath} L ${last.x} ${bottomY} L ${first.x} ${bottomY} Z`;
+      } else if (points.length === 1) {
+        const only = points[0]!;
+        smoothPath = `M ${only.x} ${only.y}`;
+      }
+
+      const gradientId = `line-gradient-${Math.random().toString(36).slice(2, 8)}`;
 
       return (
-        <div className="space-y-2">
+        <div className="space-y-3">
           {props.title && (
-            <div className="text-sm font-medium text-left">{props.title}</div>
+            <div className="text-sm font-medium">{props.title}</div>
           )}
-          <div className="relative h-28">
-            <svg viewBox={`0 0 ${width} ${height}`} className="w-full h-full">
-              <line
-                x1={padding.left}
-                y1={padding.top + chartHeight / 2}
-                x2={width - padding.right}
-                y2={padding.top + chartHeight / 2}
-                stroke="currentColor"
-                strokeOpacity="0.1"
-                strokeWidth="1"
-              />
-              <line
-                x1={padding.left}
-                y1={padding.top}
-                x2={width - padding.right}
-                y2={padding.top}
-                stroke="currentColor"
-                strokeOpacity="0.1"
-                strokeWidth="1"
-              />
-              <line
-                x1={padding.left}
-                y1={height - padding.bottom}
-                x2={width - padding.right}
-                y2={height - padding.bottom}
-                stroke="currentColor"
-                strokeOpacity="0.1"
-                strokeWidth="1"
-              />
-              {pathD && (
+          <div className="relative" style={{ height: 160 }}>
+            <svg
+              viewBox={`0 0 ${width} ${height}`}
+              className="w-full h-full"
+              preserveAspectRatio="none"
+            >
+              <defs>
+                <linearGradient id={gradientId} x1="0" y1="0" x2="0" y2="1">
+                  <stop
+                    offset="0%"
+                    stopColor="currentColor"
+                    stopOpacity="0.15"
+                  />
+                  <stop
+                    offset="100%"
+                    stopColor="currentColor"
+                    stopOpacity="0"
+                  />
+                </linearGradient>
+              </defs>
+              {[0, 0.25, 0.5, 0.75, 1].map((frac) => (
+                <line
+                  key={frac}
+                  x1={padding.left}
+                  y1={padding.top + chartHeight * frac}
+                  x2={width - padding.right}
+                  y2={padding.top + chartHeight * frac}
+                  stroke="currentColor"
+                  strokeOpacity="0.07"
+                  vectorEffect="non-scaling-stroke"
+                  strokeWidth="1"
+                />
+              ))}
+              {areaPath && (
                 <path
-                  d={pathD}
+                  d={areaPath}
+                  fill={`url(#${gradientId})`}
+                  className="text-primary"
+                />
+              )}
+              {smoothPath && (
+                <path
+                  d={smoothPath}
                   fill="none"
                   stroke="currentColor"
                   strokeWidth="2"
                   strokeLinecap="round"
                   strokeLinejoin="round"
+                  vectorEffect="non-scaling-stroke"
                   className="text-primary"
                 />
               )}
-              {points.map((p, i) => (
-                <circle
-                  key={i}
-                  cx={p.x}
-                  cy={p.y}
-                  r="4"
-                  className="fill-primary"
-                />
-              ))}
             </svg>
+            {points.map((p, i) => (
+              <div
+                key={i}
+                className="absolute w-[7px] h-[7px] rounded-full bg-primary -translate-x-1/2 -translate-y-1/2"
+                style={{
+                  left: `${(p.x / width) * 100}%`,
+                  top: `${(p.y / height) * 100}%`,
+                }}
+              />
+            ))}
           </div>
-          {data.length > 0 && (
-            <div className="flex justify-between">
-              {data.map((d, i) => (
-                <div
+          {points.length > 0 && (
+            <div className="relative h-4">
+              {points.map((p, i) => (
+                <span
                   key={i}
-                  className="text-xs text-muted-foreground text-center"
-                  style={{ width: `${100 / data.length}%` }}
+                  className="absolute text-[11px] text-muted-foreground -translate-x-1/2"
+                  style={{ left: `${(p.x / width) * 100}%` }}
                 >
-                  {d.label}
-                </div>
+                  {data[i]?.label}
+                </span>
               ))}
             </div>
           )}
@@ -787,7 +1016,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       );
 
       return (
-        <div className="space-y-2">
+        <div className="w-full space-y-2">
           {props.label && <Label htmlFor={props.name}>{props.label}</Label>}
           <Input
             id={props.name}
@@ -829,7 +1058,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       );
 
       return (
-        <div className="space-y-2">
+        <div className="w-full space-y-2">
           {props.label && <Label htmlFor={props.name}>{props.label}</Label>}
           <Textarea
             id={props.name}
@@ -872,7 +1101,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       );
 
       return (
-        <div className="space-y-2">
+        <div className="w-full space-y-2">
           <Label>{props.label}</Label>
           <Select
             value={value}
@@ -945,7 +1174,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       const setValue = isBound ? setBoundValue : setLocalValue;
 
       return (
-        <div className="space-y-2">
+        <div className="w-full space-y-2">
           {props.label && <Label>{props.label}</Label>}
           <RadioGroup
             value={value}
@@ -987,7 +1216,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       const setChecked = isBound ? setBoundChecked : setLocalChecked;
 
       return (
-        <div className="flex items-center justify-between space-x-2">
+        <div className="w-full flex items-center justify-between space-x-2">
           <Label htmlFor={props.name} className="cursor-pointer">
             {props.label}
           </Label>
@@ -1014,7 +1243,7 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       const setValue = isBound ? setBoundValue : setLocalValue;
 
       return (
-        <div className="space-y-2">
+        <div className="w-full space-y-2">
           {props.label && (
             <div className="flex justify-between">
               <Label className="text-sm">{props.label}</Label>
@@ -1041,9 +1270,11 @@ export const { registry, executeAction } = defineRegistry(playgroundCatalog, {
       const variant =
         props.variant === "danger"
           ? "destructive"
-          : props.variant === "secondary"
-            ? "secondary"
-            : "default";
+          : props.variant === "outline"
+            ? "outline"
+            : props.variant === "secondary"
+              ? "secondary"
+              : "default";
 
       return (
         <Button

apps/web/lib/render/renderer.tsx

@@ -11,8 +11,11 @@ import {
   ValidationProvider,
   useValidation,
 } from "@json-render/react";
+import { JsonRenderDevtools } from "@json-render/devtools-react";
+import type { Catalog } from "@json-render/core";
 
 import { registry, Fallback } from "./registry";
+import { playgroundCatalog } from "./catalog";
 
 // =============================================================================
 // PlaygroundRenderer
@@ -22,6 +25,8 @@ interface PlaygroundRendererProps {
   spec: Spec | null;
   data?: Record<string, unknown>;
   loading?: boolean;
+  /** Show the json-render devtools panel. Default: false. */
+  devtools?: boolean;
 }
 
 const fallbackRenderer = (renderProps: { element: { type: string } }) => (
@@ -72,6 +77,7 @@ export function PlaygroundRenderer({
   spec,
   data,
   loading,
+  devtools,
 }: PlaygroundRendererProps): ReactNode {
   if (!spec) return null;
 
@@ -86,6 +92,12 @@ export function PlaygroundRenderer({
               fallback={fallbackRenderer}
               loading={loading}
             />
+            {devtools ? (
+              <JsonRenderDevtools
+                spec={spec}
+                catalog={playgroundCatalog as unknown as Catalog}
+              />
+            ) : null}
           </ValidatedActions>
         </ValidationProvider>
       </VisibilityProvider>

apps/web/lib/spec-patch.ts

@@ -35,6 +35,10 @@ export function setSpecValue(
         type: typeof el.type === "string" ? el.type : "",
         props: el.props != null && typeof el.props === "object" ? el.props : {},
         children: Array.isArray(el.children) ? el.children : [],
+        slots:
+          el.slots != null && typeof el.slots === "object"
+            ? el.slots
+            : undefined,
       } as Spec["elements"][string];
     } else {
       const element = newSpec.elements[elementKey];

apps/web/package.json

@@ -1,6 +1,6 @@
 {
   "name": "web",
-  "version": "0.1.10",
+  "version": "0.1.11",
   "type": "module",
   "private": true,
   "license": "Apache-2.0",
@@ -17,6 +17,8 @@
     "@ai-sdk/react": "3.0.79",
     "@json-render/codegen": "workspace:*",
     "@json-render/core": "workspace:*",
+    "@json-render/devtools": "workspace:*",
+    "@json-render/devtools-react": "workspace:*",
     "@json-render/react": "workspace:*",
     "@json-render/yaml": "workspace:*",
     "@mdx-js/loader": "^3.1.1",

examples/chat/CHANGELOG.md

@@ -1,5 +1,14 @@
 # example-chat
 
+## 0.1.11
+
+### Patch Changes
+
+- Updated dependencies [519a538]
+  - @json-render/core@0.16.0
+  - @json-render/react@0.16.0
+  - @json-render/shadcn@0.16.0
+
 ## 0.1.10
 
 ### Patch Changes

examples/chat/README.md

@@ -0,0 +1,50 @@
+# Chat Example
+
+An AI-powered data explorer that streams rich, interactive UI directly into a chat interface. The assistant uses tool calls to fetch real data (weather, GitHub, crypto, Hacker News, web search), then generates a json-render spec that renders inline alongside the conversation using shadcn components, Recharts, and React Three Fiber.
+
+## What it shows
+
+- **Streaming specs inside chat messages** -- `pipeJsonRender` on the server merges the AI SDK UI stream with json-render spec patches so text, tool-call indicators, and rendered UI all appear in the correct order within a single message bubble.
+- **ToolLoopAgent with live data** -- the agent loops through tool calls (weather, GitHub repos/PRs, crypto prices, Hacker News, web search) to gather real data before generating UI.
+- **Full catalog/registry stack** -- a catalog constrains what the model can produce; the registry maps every component to a real React implementation (shadcn, Recharts charts, R3F 3D scenes).
+- **State and interactivity** -- `$state`, `$bindState`, visibility, and actions work inside the streamed spec, so the rendered UI is interactive, not static.
+
+## Setup
+
+```bash
+pnpm install          # from the monorepo root
+cd examples/chat
+cp .env.example .env.local
+```
+
+Set the required environment variables in `.env.local`:
+
+| Variable | Required | Description |
+|----------|----------|-------------|
+| `AI_GATEWAY_API_KEY` | Yes | Vercel AI Gateway key (auto-authenticated on Vercel) |
+| `AI_GATEWAY_MODEL` | No | Model identifier, defaults to `anthropic/claude-haiku-4.5` |
+| `KV_REST_API_URL` | No | Upstash Redis URL for rate limiting |
+| `KV_REST_API_TOKEN` | No | Upstash Redis token |
+| `RATE_LIMIT_PER_MINUTE` | No | Defaults to `10` |
+| `RATE_LIMIT_PER_DAY` | No | Defaults to `100` |
+
+Rate limiting is a no-op when the Upstash variables are not set.
+
+## Run
+
+```bash
+pnpm dev
+# http://chat-demo.json-render.localhost:1355
+```
+
+Requires global [`portless`](https://github.com/vercel-labs/portless). The `predev` script checks for it automatically.
+
+## Files
+
+- `app/page.tsx` -- chat UI with `useChat`, message rendering, and inline spec display
+- `app/api/generate/route.ts` -- streams the agent through `pipeJsonRender` with optional Upstash rate limiting
+- `lib/agent.ts` -- `ToolLoopAgent` with system prompt from `explorerCatalog.prompt()` and custom rules for layout, 3D, and interactivity
+- `lib/tools/` -- tool definitions for weather, GitHub, crypto, Hacker News, and web search
+- `lib/render/catalog.ts` -- component catalog (shadcn base + custom metrics, tables, charts, tabs, 3D)
+- `lib/render/registry.tsx` -- maps catalog types to React components (shadcn, Recharts, R3F)
+- `lib/render/renderer.tsx` -- `ExplorerRenderer` wrapping `StateProvider`, `VisibilityProvider`, `ActionProvider`, and `Renderer`

examples/chat/next-env.d.ts

@@ -1,6 +0,0 @@
-/// <reference types="next" />
-/// <reference types="next/image-types/global" />
-import "./.next/dev/types/routes.d.ts";
-
-// NOTE: This file should not be edited
-// see https://nextjs.org/docs/app/api-reference/config/typescript for more information.

examples/chat/package.json

@@ -1,6 +1,6 @@
 {
   "name": "example-chat",
-  "version": "0.1.10",
+  "version": "0.1.11",
   "type": "module",
   "private": true,
   "scripts": {

examples/dashboard/CHANGELOG.md

@@ -1,5 +1,14 @@
 # example-dashboard
 
+## 0.1.11
+
+### Patch Changes
+
+- Updated dependencies [519a538]
+  - @json-render/core@0.16.0
+  - @json-render/codegen@0.16.0
+  - @json-render/react@0.16.0
+
 ## 0.1.10
 
 ### Patch Changes

examples/dashboard/README.md

@@ -0,0 +1,58 @@
+# Dashboard Example
+
+AI-generated dashboard widgets with guardrails. Each widget is streamed from an LLM, constrained by a json-render catalog, and rendered with shadcn components and Recharts. Widgets can fetch and mutate data through named actions that hit a real REST API backed by Postgres.
+
+## What it shows
+
+- **Streaming widget generation** -- `useUIStream` streams JSONL patches from the server, progressively building each widget's spec.
+- **Catalog-constrained actions** -- the catalog declares typed actions (`viewCustomers`, `createInvoice`, `approveExpense`, etc.) that map to REST endpoints; the registry wires them to real `fetch` calls with toast feedback.
+- **Persistence** -- widget prompts and specs are saved to Postgres via Drizzle ORM, so widgets survive page reloads.
+- **Drag-and-drop reorder** -- `@dnd-kit` lets you rearrange widgets, with ordering persisted to the database.
+- **Edit mode** -- send a follow-up prompt to iteratively refine a saved widget.
+
+## Setup
+
+```bash
+pnpm install          # from the monorepo root
+cd examples/dashboard
+cp .env.example .env
+```
+
+Set the required environment variables:
+
+| Variable | Required | Description |
+|----------|----------|-------------|
+| `DATABASE_URL` | Yes | Postgres connection string |
+| `AI_GATEWAY_API_KEY` | Yes | Vercel AI Gateway key |
+| `AI_GATEWAY_MODEL` | No | Defaults to `anthropic/claude-haiku-4.5` |
+| `KV_REST_API_URL` | No | Upstash Redis URL for rate limiting |
+| `KV_REST_API_TOKEN` | No | Upstash Redis token |
+| `RATE_LIMIT_PER_MINUTE` | No | Defaults to `10` |
+| `RATE_LIMIT_PER_DAY` | No | Defaults to `100` |
+
+Set up the database:
+
+```bash
+pnpm db:push          # apply the schema to your database
+pnpm db:seed          # optional: populate with sample data
+```
+
+## Run
+
+```bash
+pnpm dev
+# http://dashboard-demo.json-render.localhost:1355
+```
+
+Requires global [`portless`](https://github.com/vercel-labs/portless). The `predev` script checks for it automatically.
+
+## Files
+
+- `app/page.tsx` -- dashboard grid with drag-and-drop, widget management, and add/edit flows
+- `app/api/generate/route.ts` -- streams text from the model using `dashboardCatalog.prompt()` as the system prompt
+- `app/api/v1/` -- REST API for widgets, customers, invoices, expenses, accounts, and reports
+- `lib/render/catalog.ts` -- component catalog with shadcn-based UI primitives and typed business actions
+- `lib/render/registry.tsx` -- maps components to React (shadcn + Recharts) and wires actions to REST calls
+- `lib/render/renderer.tsx` -- `DashboardRenderer` with state, visibility, and action providers
+- `lib/db/schema.ts` -- Drizzle schema for customers, invoices, expenses, accounts, transactions, and widgets
+- `components/widget.tsx` -- individual widget with `useUIStream`, auto-action execution, and save/edit logic

examples/dashboard/components/header.tsx

@@ -47,7 +47,7 @@ export function Header() {
         </div>
         <nav className="flex items-center gap-4">
           <a
-            href="https://json-render.vercel.app"
+            href="https://json-render.dev"
             target="_blank"
             rel="noopener noreferrer"
             className="text-sm text-muted-foreground hover:text-foreground transition-colors"

examples/dashboard/next-env.d.ts

@@ -1,6 +0,0 @@
-/// <reference types="next" />
-/// <reference types="next/image-types/global" />
-import "./.next/dev/types/routes.d.ts";
-
-// NOTE: This file should not be edited
-// see https://nextjs.org/docs/app/api-reference/config/typescript for more information.

examples/dashboard/package.json

@@ -1,6 +1,6 @@
 {
   "name": "example-dashboard",
-  "version": "0.1.10",
+  "version": "0.1.11",
   "type": "module",
   "private": true,
   "scripts": {

examples/devtools/.env.example

@@ -0,0 +1,7 @@
+# Vercel AI Gateway
+# Get a key from https://vercel.com/ai-gateway
+# Automatically authenticated when deployed on Vercel.
+AI_GATEWAY_API_KEY=
+
+# Optional: override the model. Defaults to anthropic/claude-haiku-4.5.
+AI_GATEWAY_MODEL=

examples/devtools/README.md

@@ -0,0 +1,49 @@
+# Devtools example
+
+An AI-powered chat where each assistant reply streams a fresh `Spec` that renders inline. A single `<JsonRenderDevtools />` panel observes **every** rendered spec, **every** streamed patch, **every** state change, and **every** dispatched action across the whole page — demonstrating how one devtools instance works with many renderers.
+
+Pairs with [`@json-render/devtools`](../../packages/devtools) and [`@json-render/devtools-react`](../../packages/devtools-react).
+
+## What it shows
+
+- **AI-streamed specs (inline mode)** — the agent writes a short conversational reply, then emits a `` ```spec `` fence of RFC 6902 JSON patches. `pipeJsonRender` on the server splits that into `data-spec` parts and plain text parts; the client re-assembles both with `useJsonRenderMessage`.
+- **One renderer per assistant message, one devtools panel** — every message gets its own `<Renderer />`, but they share a single top-level `<JSONUIProvider>`, so the devtools State / Actions / Stream tabs see the whole page, not just one message.
+- **State namespacing per turn** — the API route hands the agent a unique `messageId` and requires every element key (`<id>-root`, `<id>-counter`, …) and state path (`/<id>/count`, `/<id>/todos`) to be prefixed with it, so specs from different messages never collide on shared state.
+- **Built-ins exercised** — `setState`, `pushState`, `removeState`, plus `inc`/`dec`/`toggle`/`add` computed functions, `$bindState`, `$template`, `$state`, `repeat`, `$item`, `$index`, and conditional `visible`.
+- **The Pick panel across renderers** — because every element is tagged with `data-jr-key`, picking an element in any assistant bubble jumps to its spec in the panel.
+
+## Setup
+
+```bash
+pnpm install
+cp .env.example .env.local
+# Edit .env.local and set AI_GATEWAY_API_KEY
+```
+
+Grab an AI Gateway key at <https://vercel.com/ai-gateway>. On Vercel the key is auto-authenticated, so you only need this for local dev.
+
+## Run
+
+```bash
+pnpm dev
+# http://devtools-demo.json-render.localhost:1355
+```
+
+Press <kbd>⌘</kbd> <kbd>⇧</kbd> <kbd>J</kbd> (or click the floating `{}` badge) to toggle the panel. It starts open by default.
+
+## Files
+
+- `app/page.tsx` — chat UI, top-level `<JSONUIProvider>`, per-message `<Renderer />`, `<JsonRenderDevtools>` mount
+- `app/api/chat/route.ts` — streams the agent through `pipeJsonRender`
+- `lib/agent.ts` — `ToolLoopAgent` with a system prompt that enforces inline mode + `messageId`-based namespacing
+- `lib/catalog.ts` — compact catalog (Card, Stack, Grid, Metric, Button, TextInput, Checkbox, List, ProgressBar, Callout, …) tuned to show off devtools
+- `lib/registry.tsx` — component renderers with plain inline styles, no UI framework
+
+## Try these prompts
+
+- "Build an interactive counter with + and - buttons" — Actions tab lights up with `setState` dispatches.
+- "Make a todo list where I can add items, mark them done, and remove them" — exercises `pushState` / `removeState` and `$bindState` inputs.
+- "Show me a fitness dashboard with three metrics and progress bars" — metric-heavy spec; handy for the Spec tree + State inspector.
+- "Quiz me on three geography questions with a submit button that reveals my score" — uses bindings plus conditional visibility.
+
+Then send a second prompt in the same session and watch the Stream tab keep appending patches while the State tab shows both turns' namespaced keys side by side.

examples/devtools/app/api/chat/route.ts

@@ -0,0 +1,52 @@
+import {
+  convertToModelMessages,
+  createUIMessageStream,
+  createUIMessageStreamResponse,
+  type UIMessage,
+} from "ai";
+import { pipeJsonRender } from "@json-render/core";
+import { createAgent } from "@/lib/agent";
+
+export const maxDuration = 60;
+
+export async function POST(req: Request) {
+  if (!process.env.AI_GATEWAY_API_KEY) {
+    return new Response(
+      JSON.stringify({
+        error: "Missing AI_GATEWAY_API_KEY",
+        message:
+          "Set AI_GATEWAY_API_KEY in .env.local to enable AI. See https://vercel.com/ai-gateway.",
+      }),
+      { status: 500, headers: { "Content-Type": "application/json" } },
+    );
+  }
+
+  const body = (await req.json()) as {
+    messages: UIMessage[];
+    messageId?: string;
+  };
+
+  if (!body.messages?.length) {
+    return new Response(
+      JSON.stringify({ error: "messages array is required" }),
+      { status: 400, headers: { "Content-Type": "application/json" } },
+    );
+  }
+
+  // The client generates a stable messageId per turn so the agent can
+  // namespace state paths and element keys. Fall back to a random id.
+  const messageId =
+    body.messageId ?? `m${Math.random().toString(36).slice(2, 8)}`;
+
+  const agent = createAgent(messageId);
+  const modelMessages = await convertToModelMessages(body.messages);
+  const result = await agent.stream({ messages: modelMessages });
+
+  const stream = createUIMessageStream({
+    execute: async ({ writer }) => {
+      writer.merge(pipeJsonRender(result.toUIMessageStream()));
+    },
+  });
+
+  return createUIMessageStreamResponse({ stream });
+}

examples/devtools/app/globals.css

@@ -0,0 +1,429 @@
+:root {
+  color-scheme: light;
+  --surface: #ffffff;
+  --surface-raised: #ffffff;
+  --surface-muted: #f4f4f5;
+  --border: #e4e4e7;
+  --text: #0a0a0a;
+  --text-muted: #71717a;
+  --accent: #6366f1;
+  --accent-fg: #ffffff;
+  --success: #16a34a;
+  --warn: #d97706;
+  --user-bubble-bg: #0a0a0a;
+  --user-bubble-fg: #ffffff;
+
+  font-family:
+    ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto,
+    "Helvetica Neue", sans-serif;
+  font-size: 14px;
+  line-height: 1.5;
+  -webkit-font-smoothing: antialiased;
+  color: var(--text);
+  background: var(--surface-muted);
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html,
+body {
+  margin: 0;
+  padding: 0;
+  height: 100%;
+}
+
+button,
+input,
+textarea {
+  font: inherit;
+  color: inherit;
+}
+
+a {
+  color: var(--accent);
+}
+
+code {
+  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, monospace;
+  font-size: 0.9em;
+  background: var(--surface-muted);
+  padding: 0.1em 0.35em;
+  border-radius: 4px;
+}
+
+/* Dividers between repeated list items — top border on all but the first
+   so there's no dangling line at either end. */
+.jr-list-item + .jr-list-item {
+  border-top: 1px solid var(--border);
+}
+
+@keyframes jr-shimmer {
+  0%,
+  100% {
+    opacity: 0.55;
+  }
+  50% {
+    opacity: 1;
+  }
+}
+
+.jr-shimmer {
+  animation: jr-shimmer 1.4s ease-in-out infinite;
+}
+
+kbd {
+  display: inline-block;
+  padding: 1px 5px;
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  background: var(--surface);
+  font-family:
+    ui-monospace, SFMono-Regular, "SF Mono", Menlo, monospace;
+  font-size: 11px;
+  line-height: 1.3;
+}
+
+/* ==========================================================================
+   App shell
+   ========================================================================== */
+
+.app {
+  height: 100%;
+  display: grid;
+  grid-template-rows: auto 1fr auto;
+  background: var(--surface-muted);
+}
+
+.topbar {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 10px 20px;
+  background: var(--surface);
+  border-bottom: 1px solid var(--border);
+}
+
+.topbar-brand {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+}
+
+.logo-dot {
+  width: 22px;
+  height: 22px;
+  border-radius: 6px;
+  background: linear-gradient(135deg, var(--accent), color-mix(in oklab, var(--accent) 60%, #000));
+  box-shadow: 0 0 0 2px color-mix(in oklab, var(--accent) 20%, transparent);
+}
+
+.topbar-text {
+  display: flex;
+  flex-direction: column;
+  line-height: 1.2;
+}
+
+.topbar-title {
+  font-weight: 600;
+  font-size: 14px;
+}
+
+.topbar-sub {
+  font-size: 12px;
+  color: var(--text-muted);
+}
+
+.topbar-actions {
+  display: flex;
+  gap: 8px;
+  align-items: center;
+}
+
+.btn-ghost {
+  background: transparent;
+  border: 1px solid transparent;
+  padding: 6px 10px;
+  border-radius: 8px;
+  font-size: 13px;
+  color: var(--text-muted);
+  cursor: pointer;
+}
+.btn-ghost:hover {
+  background: var(--surface-muted);
+  color: var(--text);
+}
+
+.btn-link {
+  text-decoration: none;
+  font-size: 13px;
+  color: var(--text-muted);
+  padding: 6px 10px;
+  border-radius: 8px;
+}
+.btn-link:hover {
+  background: var(--surface-muted);
+  color: var(--text);
+}
+
+.btn-primary {
+  background: var(--accent);
+  color: var(--accent-fg);
+  border: none;
+  border-radius: 8px;
+  padding: 8px 16px;
+  font-size: 13px;
+  font-weight: 500;
+  cursor: pointer;
+  transition: opacity 0.15s;
+}
+.btn-primary:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
+/* ==========================================================================
+   Scrollable chat area
+   ========================================================================== */
+
+.scroll {
+  overflow-y: auto;
+  padding: 24px 20px 40px;
+}
+
+.thread {
+  max-width: 760px;
+  margin: 0 auto;
+  display: flex;
+  flex-direction: column;
+  gap: 20px;
+}
+
+.row {
+  display: flex;
+  width: 100%;
+}
+
+.row.user {
+  justify-content: flex-end;
+}
+
+.row.assistant {
+  justify-content: flex-start;
+}
+
+.bubble.user {
+  max-width: 85%;
+  padding: 10px 14px;
+  border-radius: 16px 16px 4px 16px;
+  background: var(--user-bubble-bg);
+  color: var(--user-bubble-fg);
+  font-size: 13px;
+  line-height: 1.5;
+  white-space: pre-wrap;
+}
+
+.assistant-inner {
+  width: 100%;
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+}
+
+.assistant-text {
+  font-size: 13px;
+  line-height: 1.55;
+  white-space: pre-wrap;
+  color: var(--text);
+}
+
+.thinking {
+  font-size: 13px;
+  color: var(--text-muted);
+}
+
+/* Each rendered spec is wrapped in a structural container without any
+   visual chrome of its own — the AI-generated Card (or whatever the
+   root element is) carries the framing. `.thread` already provides the
+   gap between messages, so no outer border is needed here. */
+.spec-wrap {
+  width: 100%;
+}
+
+.error {
+  padding: 12px 14px;
+  border-radius: 10px;
+  border: 1px solid color-mix(in oklab, var(--warn) 40%, var(--border));
+  background: color-mix(in oklab, var(--warn) 10%, transparent);
+  color: var(--warn);
+  font-size: 13px;
+}
+
+/* ==========================================================================
+   Empty state
+   ========================================================================== */
+
+.empty {
+  min-height: 100%;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 40px 0;
+}
+
+.empty-inner {
+  max-width: 720px;
+  width: 100%;
+  display: flex;
+  flex-direction: column;
+  gap: 20px;
+}
+
+.eyebrow {
+  font-size: 12px;
+  font-weight: 500;
+  letter-spacing: 0.06em;
+  text-transform: uppercase;
+  color: var(--accent);
+}
+
+.empty h1 {
+  margin: 0;
+  font-size: 28px;
+  font-weight: 600;
+  letter-spacing: -0.01em;
+  line-height: 1.2;
+}
+
+.lead {
+  margin: 0;
+  font-size: 15px;
+  color: var(--text-muted);
+  line-height: 1.55;
+}
+
+.callout-row {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 12px;
+}
+@media (max-width: 620px) {
+  .callout-row {
+    grid-template-columns: 1fr;
+  }
+}
+
+.callout {
+  padding: 12px 14px;
+  border-radius: 10px;
+  border: 1px solid var(--border);
+  background: var(--surface);
+  font-size: 13px;
+  line-height: 1.5;
+}
+.callout .cap {
+  font-size: 11px;
+  font-weight: 500;
+  letter-spacing: 0.04em;
+  text-transform: uppercase;
+  color: var(--text-muted);
+  margin-bottom: 4px;
+}
+
+.sugg-grid {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 12px;
+  margin-top: 8px;
+}
+@media (max-width: 620px) {
+  .sugg-grid {
+    grid-template-columns: 1fr;
+  }
+}
+
+.sugg {
+  text-align: left;
+  background: var(--surface);
+  border: 1px solid var(--border);
+  border-radius: 12px;
+  padding: 14px;
+  cursor: pointer;
+  transition:
+    border-color 0.15s,
+    transform 0.05s;
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+.sugg:hover {
+  border-color: color-mix(in oklab, var(--accent) 40%, var(--border));
+}
+.sugg:active {
+  transform: translateY(1px);
+}
+
+.sugg-label {
+  font-size: 13px;
+  font-weight: 600;
+}
+
+.sugg-prompt {
+  font-size: 13px;
+  color: var(--text-muted);
+  line-height: 1.45;
+}
+
+.sugg-blurb {
+  font-size: 11px;
+  color: var(--accent);
+  margin-top: 4px;
+}
+
+/* ==========================================================================
+   Composer
+   ========================================================================== */
+
+.composer {
+  background: var(--surface);
+  border-top: 1px solid var(--border);
+  padding: 12px 20px 14px;
+}
+
+.composer-inner {
+  max-width: 760px;
+  margin: 0 auto;
+  display: flex;
+  gap: 8px;
+  align-items: flex-end;
+}
+
+.composer textarea {
+  flex: 1;
+  resize: none;
+  padding: 10px 12px;
+  border-radius: 10px;
+  border: 1px solid var(--border);
+  background: var(--surface);
+  color: var(--text);
+  font-size: 13px;
+  line-height: 1.5;
+  outline: none;
+  min-height: 58px;
+}
+.composer textarea:focus {
+  border-color: color-mix(in oklab, var(--accent) 50%, var(--border));
+}
+
+.composer .btn-primary {
+  padding: 10px 18px;
+  align-self: stretch;
+}
+
+.composer-hint {
+  max-width: 760px;
+  margin: 6px auto 0;
+  font-size: 11px;
+  color: var(--text-muted);
+}

examples/devtools/app/layout.tsx

@@ -0,0 +1,18 @@
+import type { Metadata } from "next";
+import "./globals.css";
+
+export const metadata: Metadata = {
+  title: "json-render devtools",
+  description:
+    "Interactive devtools demo: AI-streamed json-render specs, one renderer per chat message, all inspected by the floating panel.",
+};
+
+export default function RootLayout({
+  children,
+}: Readonly<{ children: React.ReactNode }>) {
+  return (
+    <html lang="en">
+      <body>{children}</body>
+    </html>
+  );
+}

examples/devtools/app/page.tsx

@@ -0,0 +1,356 @@
+"use client";
+
+import {
+  useCallback,
+  useEffect,
+  useMemo,
+  useRef,
+  useState,
+  type ReactNode,
+} from "react";
+import { useChat } from "@ai-sdk/react";
+import { DefaultChatTransport, type UIMessage } from "ai";
+import {
+  SPEC_DATA_PART,
+  type SpecDataPart,
+  type Spec,
+} from "@json-render/core";
+import {
+  JSONUIProvider,
+  Renderer,
+  buildSpecFromParts,
+  useJsonRenderMessage,
+  useStateStore,
+} from "@json-render/react";
+import { JsonRenderDevtools } from "@json-render/devtools-react";
+import { registry } from "@/lib/registry";
+import { catalog } from "@/lib/catalog";
+
+// Shared computed helpers the AI can reference with $computed. Keeping these
+// minimal avoids surprising the agent: +/-/toggle cover the most common cases.
+const computedFunctions = {
+  inc: (args: Record<string, unknown>) =>
+    ((args.of as number | undefined) ?? 0) +
+    ((args.by as number | undefined) ?? 1),
+  dec: (args: Record<string, unknown>) =>
+    ((args.of as number | undefined) ?? 0) -
+    ((args.by as number | undefined) ?? 1),
+  toggle: (args: Record<string, unknown>) => !(args.of as boolean | undefined),
+  add: (args: Record<string, unknown>) =>
+    ((args.a as number | undefined) ?? 0) +
+    ((args.b as number | undefined) ?? 0),
+};
+
+// ---------------------------------------------------------------------------
+// Types & transport
+// ---------------------------------------------------------------------------
+
+type AppDataParts = { [SPEC_DATA_PART]: SpecDataPart };
+type AppMessage = UIMessage<unknown, AppDataParts>;
+
+const transport = new DefaultChatTransport({ api: "/api/chat" });
+
+const SUGGESTIONS = [
+  {
+    label: "Counter",
+    prompt: "Build an interactive counter with +/- and reset buttons",
+    blurb: "Dispatches setState actions visible in the Actions panel.",
+  },
+  {
+    label: "Todo list",
+    prompt:
+      "Make a todo list where I can type a task, add it, mark it done, and remove it",
+    blurb: "Shows pushState / removeState and two-way bound inputs.",
+  },
+  {
+    label: "Dashboard",
+    prompt:
+      "Show me a fitness tracker with three metrics (steps, calories, sleep), progress bars, and a tip callout",
+    blurb: "Metrics + progress — good State and Stream panel content.",
+  },
+  {
+    label: "Quiz",
+    prompt:
+      "Quiz me on three world geography questions with checkboxes and a submit button that reveals my score",
+    blurb: "Bindings + conditional visibility in the Spec panel.",
+  },
+];
+
+// ---------------------------------------------------------------------------
+// MessageSpecRenderer — one <Renderer /> per assistant message, all wired
+// into the same top-level state store so the devtools sees everything.
+// ---------------------------------------------------------------------------
+
+function MessageSpecRenderer({ spec }: { spec: Spec }): ReactNode {
+  const { update, getSnapshot } = useStateStore();
+  const seeded = useRef<Set<string>>(new Set());
+
+  // Seed the shared store with this message's initial state the first time
+  // each top-level key appears. The AI is prompted to namespace every path
+  // with the message id, so keys from different messages never collide.
+  // We only seed keys that aren't already in the store, so live user edits
+  // aren't clobbered by late-arriving patches.
+  useEffect(() => {
+    const branch = spec.state as Record<string, unknown> | undefined;
+    if (!branch) return;
+    const current = getSnapshot() as Record<string, unknown>;
+    const updates: Record<string, unknown> = {};
+    for (const [key, value] of Object.entries(branch)) {
+      if (seeded.current.has(key)) continue;
+      seeded.current.add(key);
+      if (current[key] === undefined) {
+        updates[`/${key}`] = value;
+      }
+    }
+    if (Object.keys(updates).length > 0) {
+      update(updates);
+    }
+  }, [spec.state, update, getSnapshot]);
+
+  return (
+    <div className="spec-wrap">
+      <Renderer spec={spec} registry={registry} />
+    </div>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Bubbles
+// ---------------------------------------------------------------------------
+
+function UserBubble({ text }: { text: string }) {
+  return (
+    <div className="row user">
+      <div className="bubble user">{text}</div>
+    </div>
+  );
+}
+
+function AssistantBubble({
+  message,
+  isLast,
+  isStreaming,
+}: {
+  message: AppMessage;
+  isLast: boolean;
+  isStreaming: boolean;
+}) {
+  const { spec, text, hasSpec } = useJsonRenderMessage(message.parts);
+  const showThinking = isLast && isStreaming && !text && !hasSpec;
+
+  return (
+    <div className="row assistant">
+      <div className="assistant-inner">
+        {showThinking && <div className="thinking jr-shimmer">Thinking…</div>}
+        {text && <div className="assistant-text">{text}</div>}
+        {hasSpec && spec && <MessageSpecRenderer spec={spec} />}
+      </div>
+    </div>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Empty state
+// ---------------------------------------------------------------------------
+
+function EmptyState({ onPick }: { onPick: (prompt: string) => void }) {
+  return (
+    <div className="empty">
+      <div className="empty-inner">
+        <div className="eyebrow">json-render devtools</div>
+        <h1>Chat with AI, inspect every renderer.</h1>
+        <p className="lead">
+          Each assistant reply streams a fresh <code>Spec</code> rendered inline
+          below the message. One floating devtools panel captures every streamed
+          patch, state change, and dispatched action — across every message on
+          this page.
+        </p>
+        <div className="callout-row">
+          <div className="callout">
+            <div className="cap">Tip</div>
+            <div>
+              The panel is already open. Switch between Spec, State, Actions,
+              Stream, Catalog and Pick to see what each renderer exposes.
+            </div>
+          </div>
+          <div className="callout">
+            <div className="cap">Shortcut</div>
+            <div>
+              Toggle the panel with <kbd>⌘</kbd> <kbd>⇧</kbd> <kbd>J</kbd> or
+              click the <code>{"{}"}</code> badge.
+            </div>
+          </div>
+        </div>
+
+        <div className="sugg-grid">
+          {SUGGESTIONS.map((s) => (
+            <button
+              key={s.label}
+              type="button"
+              className="sugg"
+              onClick={() => onPick(s.prompt)}
+            >
+              <div className="sugg-label">{s.label}</div>
+              <div className="sugg-prompt">{s.prompt}</div>
+              <div className="sugg-blurb">{s.blurb}</div>
+            </button>
+          ))}
+        </div>
+      </div>
+    </div>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Page
+// ---------------------------------------------------------------------------
+
+export default function Page() {
+  const [input, setInput] = useState("");
+  const listRef = useRef<HTMLDivElement>(null);
+  const taRef = useRef<HTMLTextAreaElement>(null);
+
+  const { messages, sendMessage, setMessages, status, error } =
+    useChat<AppMessage>({ transport });
+
+  const isStreaming = status === "streaming" || status === "submitted";
+
+  // The devtools Spec panel inspects one spec at a time; we show the most
+  // recent assistant message's spec as a sensible default.
+  const currentSpec = useMemo<Spec | null>(() => {
+    for (let i = messages.length - 1; i >= 0; i--) {
+      const m = messages[i];
+      if (m.role !== "assistant") continue;
+      const spec = buildSpecFromParts(m.parts);
+      if (spec) return spec;
+    }
+    return null;
+  }, [messages]);
+
+  const handleSubmit = useCallback(
+    (preset?: string) => {
+      const text = (preset ?? input).trim();
+      if (!text || isStreaming) return;
+      setInput("");
+      void sendMessage({ text });
+      taRef.current?.focus();
+    },
+    [input, isStreaming, sendMessage],
+  );
+
+  // Auto-scroll to bottom on new content.
+  useEffect(() => {
+    const el = listRef.current;
+    if (!el) return;
+    el.scrollTop = el.scrollHeight;
+  }, [messages, isStreaming]);
+
+  return (
+    <JSONUIProvider
+      registry={registry}
+      initialState={{}}
+      functions={computedFunctions}
+    >
+      <div className="app">
+        <header className="topbar">
+          <div className="topbar-brand">
+            <div className="logo-dot" aria-hidden />
+            <div className="topbar-text">
+              <div className="topbar-title">json-render devtools</div>
+              <div className="topbar-sub">
+                AI chat · shared state · one panel
+              </div>
+            </div>
+          </div>
+          <div className="topbar-actions">
+            {messages.length > 0 && (
+              <button
+                className="btn-ghost"
+                onClick={() => setMessages([])}
+                type="button"
+              >
+                Clear chat
+              </button>
+            )}
+            <a
+              className="btn-link"
+              href="https://json-render.dev/docs/devtools"
+              target="_blank"
+              rel="noreferrer"
+            >
+              Docs ↗
+            </a>
+          </div>
+        </header>
+
+        <main ref={listRef} className="scroll">
+          {messages.length === 0 ? (
+            <EmptyState onPick={(p) => handleSubmit(p)} />
+          ) : (
+            <div className="thread">
+              {messages.map((m, i) => {
+                const isLast = i === messages.length - 1;
+                if (m.role === "user") {
+                  const t = m.parts
+                    .filter((p) => p.type === "text")
+                    .map((p) => (p as { text: string }).text)
+                    .join("");
+                  return <UserBubble key={m.id} text={t} />;
+                }
+                return (
+                  <AssistantBubble
+                    key={m.id}
+                    message={m}
+                    isLast={isLast}
+                    isStreaming={isStreaming}
+                  />
+                );
+              })}
+              {error && <div className="error">{error.message}</div>}
+            </div>
+          )}
+        </main>
+
+        <div className="composer">
+          <div className="composer-inner">
+            <textarea
+              ref={taRef}
+              value={input}
+              onChange={(e) => setInput(e.target.value)}
+              onKeyDown={(e) => {
+                if (e.key === "Enter" && !e.shiftKey) {
+                  e.preventDefault();
+                  handleSubmit();
+                }
+              }}
+              placeholder={
+                messages.length === 0
+                  ? "Ask the AI to build a counter, a todo list, a dashboard…"
+                  : "Ask a follow-up…"
+              }
+              rows={2}
+            />
+            <button
+              type="button"
+              onClick={() => handleSubmit()}
+              disabled={!input.trim() || isStreaming}
+              className="btn-primary"
+            >
+              {isStreaming ? "…" : "Send"}
+            </button>
+          </div>
+          <div className="composer-hint">
+            Toggle devtools with <kbd>⌘</kbd> <kbd>⇧</kbd> <kbd>J</kbd>.
+          </div>
+        </div>
+      </div>
+
+      <JsonRenderDevtools
+        spec={currentSpec}
+        catalog={catalog}
+        messages={messages}
+        initialOpen
+      />
+    </JSONUIProvider>
+  );
+}

examples/devtools/eslint.config.js

@@ -0,0 +1,11 @@
+import { nextJsConfig } from "@internal/eslint-config/next-js";
+
+/** @type {import("eslint").Linter.Config[]} */
+export default [
+  ...nextJsConfig,
+  {
+    rules: {
+      "react/prop-types": "off",
+    },
+  },
+];

examples/devtools/lib/agent.ts

@@ -0,0 +1,91 @@
+import { ToolLoopAgent, stepCountIs } from "ai";
+import { gateway } from "@ai-sdk/gateway";
+import { catalog } from "./catalog";
+
+const DEFAULT_MODEL = "anthropic/claude-haiku-4.5";
+
+/**
+ * Build a system prompt for a single assistant turn. Each turn is bound to
+ * a unique `messageId` so the generated spec's state paths and element keys
+ * can be namespaced — this lets multiple rendered UIs share one top-level
+ * state store without collisions, which is exactly what makes the devtools
+ * State and Stream panels coherent across the chat.
+ */
+function systemPrompt(messageId: string): string {
+  return `You are a generative-UI assistant. For each user turn you respond conversationally, then optionally emit a json-render UI spec describing an interactive widget, dashboard, or list.
+
+HOW TO RESPOND
+- Write one or two sentences of plain conversational text first.
+- When generating UI, follow with a \`\`\`spec code fence containing JSONL patches (RFC 6902 JSON Patch, one per line).
+- If the user's message does not require a UI (a greeting, question about you, etc.), respond with text only.
+
+STATE NAMESPACING (CRITICAL)
+- All messages in this chat share one devtools-visible state store.
+- You MUST namespace every state path and element key with the current turn id: \`${messageId}\`.
+- Element keys: use the format \`${messageId}-<name>\` (e.g. \`${messageId}-root\`, \`${messageId}-counter-value\`).
+- State paths: use \`/${messageId}/<path>\` (e.g. \`/${messageId}/count\`, \`/${messageId}/todos\`).
+- Set \`/root\` to your root element key so the renderer knows where to start.
+- Emit \`{"op":"add","path":"/state/${messageId}","value":{ ...initial state... }}\` ONCE to seed state.
+
+INTERACTION
+- Prefer interactive designs: buttons that dispatch setState/pushState/removeState, text inputs with \`$bindState\`, checkboxes with \`$bindState\`.
+- Every dispatched action, every state change, every streaming patch, and every rendered element will be visible in the json-render devtools panel — favour designs that exercise these surfaces.
+
+BUILT-IN ACTIONS
+- \`setState\` — params: { statePath: "/${messageId}/foo", value: <any> }
+- \`pushState\` — params: { statePath: "/${messageId}/list", value: <any> }
+- \`removeState\` — params: { statePath: "/${messageId}/list", index: <number> }
+
+COMPUTED FUNCTIONS (available for \`$computed\`)
+- \`inc\` — returns \`(of ?? 0) + (by ?? 1)\`. Use for + buttons: pass the current value via \`of\`.
+- \`dec\` — returns \`(of ?? 0) - (by ?? 1)\`. Use for − buttons.
+- \`toggle\` — returns \`!(of ?? false)\`. Use for boolean flips.
+- \`add\` — returns \`(a ?? 0) + (b ?? 0)\`.
+
+Example — incrementing a counter at \`/${messageId}/count\`:
+\`\`\`
+{"op":"add","path":"/elements/${messageId}-inc","value":{"type":"Button","props":{"label":"+ Increment"},"on":{"press":{"action":"setState","params":{"statePath":"/${messageId}/count","value":{"$computed":"inc","args":{"of":{"$state":"/${messageId}/count"}}}}}},"children":[]}}
+\`\`\`
+
+EXPRESSIONS
+- \`{ "$state": "/${messageId}/count" }\` reads state.
+- \`{ "$bindState": "/${messageId}/text" }\` two-way-binds inputs.
+- \`{ "$template": "hi \${/${messageId}/name}" }\` for string interpolation.
+- \`"visible": { "$state": "/${messageId}/submitted", "eq": true }\` for conditional visibility.
+- \`"repeat": { "statePath": "/${messageId}/items" }\` to iterate an array; inside repeat use \`{ "$item": "/field" }\` or \`{ "$index": true }\`.
+- For lists, the repeated element renders once per array item with \`$item\` resolving to that item.
+
+LAYOUT TIPS
+- Root is usually a Card containing a Stack (or a direct Stack).
+- Use Grid with columns="2" or "3" for metric dashboards.
+- Use Row gap="sm" align="between" for button toolbars.
+- NEVER nest a Card inside a Card — use Stack or Heading for sub-sections.
+- Divider is for separating *unrelated* content groups only. Do NOT insert a
+  Divider between siblings of a Stack that already has \`gap\` — the gap is
+  the separator. A list and its own form/toolbar are one group, not two.
+- Keep specs concise: 8-20 elements is a sweet spot.
+
+${catalog.prompt({
+  mode: "inline",
+  customRules: [
+    "Keep responses self-contained — the rendered UI will appear inline within this chat message.",
+    `Prefix EVERY element key with "${messageId}-" and EVERY state path under "/${messageId}/".`,
+    "Always seed /state with initial values BEFORE any elements that reference them.",
+    "Prefer interactive demos (counters, todo lists, quizzes, filters) over static content — they showcase the devtools Actions and State panels.",
+  ],
+})}`;
+}
+
+/**
+ * Build a fresh agent per request. Each request includes the assistant
+ * message id so the system prompt can embed it and keep state namespaced.
+ */
+export function createAgent(messageId: string) {
+  return new ToolLoopAgent({
+    model: gateway(process.env.AI_GATEWAY_MODEL || DEFAULT_MODEL),
+    instructions: systemPrompt(messageId),
+    tools: {},
+    stopWhen: stepCountIs(1),
+    temperature: 0.7,
+  });
+}

examples/devtools/lib/catalog.ts

@@ -0,0 +1,151 @@
+import { defineCatalog } from "@json-render/core";
+import { schema } from "@json-render/react/schema";
+import { z } from "zod";
+
+/**
+ * A compact, opinionated catalog focused on interactive UI patterns that
+ * show up well in the devtools panel: state changes, action dispatches,
+ * input bindings, conditional visibility, and repeated lists.
+ */
+export const catalog = defineCatalog(schema, {
+  components: {
+    Card: {
+      props: z.object({
+        title: z.string().nullable(),
+        subtitle: z.string().nullable(),
+        tone: z
+          .enum(["default", "accent", "success", "warn", "muted"])
+          .nullable(),
+      }),
+      slots: ["default"],
+      description: "Container with optional title/subtitle.",
+    },
+    Heading: {
+      props: z.object({
+        text: z.string(),
+        level: z.enum(["1", "2", "3"]).nullable(),
+      }),
+      description: "Section heading. level defaults to 2.",
+    },
+    Text: {
+      props: z.object({
+        text: z.string(),
+        muted: z.boolean().nullable(),
+        weight: z.enum(["regular", "medium", "bold"]).nullable(),
+      }),
+      description: "Paragraph text.",
+    },
+    Stack: {
+      props: z.object({
+        gap: z.enum(["xs", "sm", "md", "lg"]).nullable(),
+      }),
+      slots: ["default"],
+      description: "Vertical stack with gap.",
+    },
+    Row: {
+      props: z.object({
+        gap: z.enum(["xs", "sm", "md", "lg"]).nullable(),
+        align: z.enum(["start", "center", "end", "between"]).nullable(),
+      }),
+      slots: ["default"],
+      description: "Horizontal row with gap.",
+    },
+    Grid: {
+      props: z.object({
+        columns: z.enum(["2", "3", "4"]).nullable(),
+        gap: z.enum(["xs", "sm", "md", "lg"]).nullable(),
+      }),
+      slots: ["default"],
+      description: "Multi-column grid layout.",
+    },
+    Metric: {
+      props: z.object({
+        label: z.string(),
+        value: z.string(),
+        delta: z.string().nullable(),
+        trend: z.enum(["up", "down", "flat"]).nullable(),
+      }),
+      description: "Single labelled metric with optional delta + trend.",
+    },
+    Badge: {
+      props: z.object({
+        label: z.string(),
+        tone: z
+          .enum(["default", "accent", "success", "warn", "muted"])
+          .nullable(),
+      }),
+      description: "Small pill-shaped label.",
+    },
+    Divider: {
+      props: z.object({}),
+      description: "Horizontal rule.",
+    },
+    Button: {
+      props: z.object({
+        label: z.string(),
+        variant: z.enum(["primary", "secondary", "ghost"]).nullable(),
+        size: z.enum(["sm", "md"]).nullable(),
+        disabled: z.boolean().nullable(),
+      }),
+      description:
+        "Clickable button. Use on.press to trigger actions (setState, pushState, removeState).",
+    },
+    TextInput: {
+      props: z.object({
+        value: z.string().nullable(),
+        placeholder: z.string().nullable(),
+      }),
+      description:
+        "Text input. Use { $bindState: '/path' } on value for two-way binding.",
+    },
+    Checkbox: {
+      props: z.object({
+        label: z.string().nullable(),
+        checked: z.boolean().nullable(),
+      }),
+      description:
+        "Checkbox. Use { $bindState: '/path' } on checked for two-way binding.",
+    },
+    ProgressBar: {
+      props: z.object({
+        value: z.number(),
+        max: z.number().nullable(),
+        tone: z.enum(["default", "accent", "success", "warn"]).nullable(),
+      }),
+      description:
+        "Horizontal progress bar. value is [0, max]. max defaults to 100.",
+    },
+    Callout: {
+      props: z.object({
+        title: z.string().nullable(),
+        text: z.string(),
+        tone: z.enum(["info", "success", "warn", "tip"]).nullable(),
+      }),
+      description: "Highlighted note / tip / warning box.",
+    },
+    List: {
+      props: z.object({}),
+      slots: ["default"],
+      description:
+        "Vertical list container. Pair with repeat to iterate an array.",
+    },
+    ListItem: {
+      props: z.object({
+        title: z.string(),
+        description: z.string().nullable(),
+        meta: z.string().nullable(),
+      }),
+      description: "Single list row.",
+    },
+    Avatar: {
+      props: z.object({
+        initials: z.string(),
+        tone: z.enum(["default", "accent", "success", "warn"]).nullable(),
+      }),
+      description: "Circular avatar with 1-2 initials.",
+    },
+  },
+  actions: {},
+});
+
+export type DemoCatalog = typeof catalog;

examples/devtools/lib/registry.tsx

@@ -0,0 +1,466 @@
+import { defineRegistry, useBoundProp } from "@json-render/react";
+import { catalog } from "./catalog";
+
+// ---------------------------------------------------------------------------
+// Shared tokens
+// ---------------------------------------------------------------------------
+
+const gapMap = { xs: 4, sm: 8, md: 12, lg: 20 } as const;
+
+const cardToneBg = {
+  default: "var(--surface-raised)",
+  accent: "color-mix(in oklab, var(--accent) 8%, var(--surface-raised))",
+  success: "color-mix(in oklab, var(--success) 8%, var(--surface-raised))",
+  warn: "color-mix(in oklab, var(--warn) 10%, var(--surface-raised))",
+  muted: "var(--surface-muted)",
+} as const;
+
+const cardToneBorder = {
+  default: "var(--border)",
+  accent: "color-mix(in oklab, var(--accent) 45%, var(--border))",
+  success: "color-mix(in oklab, var(--success) 45%, var(--border))",
+  warn: "color-mix(in oklab, var(--warn) 45%, var(--border))",
+  muted: "var(--border)",
+} as const;
+
+const badgeTones = {
+  default: { bg: "var(--surface-muted)", fg: "var(--text)" },
+  accent: {
+    bg: "color-mix(in oklab, var(--accent) 15%, transparent)",
+    fg: "var(--accent)",
+  },
+  success: {
+    bg: "color-mix(in oklab, var(--success) 15%, transparent)",
+    fg: "var(--success)",
+  },
+  warn: {
+    bg: "color-mix(in oklab, var(--warn) 15%, transparent)",
+    fg: "var(--warn)",
+  },
+  muted: { bg: "var(--surface-muted)", fg: "var(--text-muted)" },
+} as const;
+
+// ---------------------------------------------------------------------------
+// Registry
+// ---------------------------------------------------------------------------
+
+export const { registry } = defineRegistry(catalog, {
+  components: {
+    Card: ({ props, children }) => {
+      const tone = props.tone ?? "default";
+      return (
+        <div
+          style={{
+            padding: 16,
+            borderRadius: 12,
+            border: `1px solid ${cardToneBorder[tone]}`,
+            background: cardToneBg[tone],
+            display: "flex",
+            flexDirection: "column",
+            gap: 12,
+          }}
+        >
+          {(props.title || props.subtitle) && (
+            <div style={{ display: "flex", flexDirection: "column", gap: 2 }}>
+              {props.title && (
+                <div style={{ fontWeight: 600, fontSize: 14 }}>
+                  {props.title}
+                </div>
+              )}
+              {props.subtitle && (
+                <div style={{ fontSize: 12, color: "var(--text-muted)" }}>
+                  {props.subtitle}
+                </div>
+              )}
+            </div>
+          )}
+          {children}
+        </div>
+      );
+    },
+
+    Heading: ({ props }) => {
+      const level = props.level ?? "2";
+      const sizes = { "1": 22, "2": 16, "3": 13 } as const;
+      const Tag = `h${level}` as unknown as "h1";
+      return (
+        <Tag
+          style={{
+            margin: 0,
+            fontWeight: 600,
+            fontSize: sizes[level],
+            lineHeight: 1.3,
+          }}
+        >
+          {props.text}
+        </Tag>
+      );
+    },
+
+    Text: ({ props }) => {
+      const weight =
+        props.weight === "bold" ? 700 : props.weight === "medium" ? 500 : 400;
+      return (
+        <p
+          style={{
+            margin: 0,
+            fontSize: 13,
+            lineHeight: 1.5,
+            fontWeight: weight,
+            color: props.muted ? "var(--text-muted)" : "var(--text)",
+          }}
+        >
+          {props.text}
+        </p>
+      );
+    },
+
+    Stack: ({ props, children }) => (
+      <div
+        style={{
+          display: "flex",
+          flexDirection: "column",
+          gap: gapMap[props.gap ?? "sm"],
+        }}
+      >
+        {children}
+      </div>
+    ),
+
+    Row: ({ props, children }) => {
+      const alignMap = {
+        start: "flex-start",
+        center: "center",
+        end: "flex-end",
+        between: "space-between",
+      } as const;
+      return (
+        <div
+          style={{
+            display: "flex",
+            flexDirection: "row",
+            gap: gapMap[props.gap ?? "sm"],
+            alignItems: "center",
+            justifyContent: alignMap[props.align ?? "start"],
+            flexWrap: "wrap",
+          }}
+        >
+          {children}
+        </div>
+      );
+    },
+
+    Grid: ({ props, children }) => (
+      <div
+        style={{
+          display: "grid",
+          gridTemplateColumns: `repeat(${props.columns ?? "2"}, minmax(0, 1fr))`,
+          gap: gapMap[props.gap ?? "md"],
+        }}
+      >
+        {children}
+      </div>
+    ),
+
+    Metric: ({ props }) => {
+      const trendColor =
+        props.trend === "up"
+          ? "var(--success)"
+          : props.trend === "down"
+            ? "var(--warn)"
+            : "var(--text-muted)";
+      const trendGlyph =
+        props.trend === "up" ? "↑" : props.trend === "down" ? "↓" : "→";
+      return (
+        <div style={{ display: "flex", flexDirection: "column", gap: 2 }}>
+          <div style={{ fontSize: 11, color: "var(--text-muted)" }}>
+            {props.label}
+          </div>
+          <div style={{ fontSize: 24, fontWeight: 600, lineHeight: 1.1 }}>
+            {props.value}
+          </div>
+          {props.delta && (
+            <div style={{ fontSize: 11, color: trendColor }}>
+              {trendGlyph} {props.delta}
+            </div>
+          )}
+        </div>
+      );
+    },
+
+    Badge: ({ props }) => {
+      const tone = badgeTones[props.tone ?? "default"];
+      return (
+        <span
+          style={{
+            display: "inline-flex",
+            alignItems: "center",
+            padding: "2px 8px",
+            borderRadius: 999,
+            fontSize: 11,
+            fontWeight: 500,
+            background: tone.bg,
+            color: tone.fg,
+          }}
+        >
+          {props.label}
+        </span>
+      );
+    },
+
+    Divider: () => (
+      <hr
+        style={{
+          border: 0,
+          borderTop: "1px solid var(--border)",
+          margin: 0,
+        }}
+      />
+    ),
+
+    Button: ({ props, emit }) => {
+      const variant = props.variant ?? "primary";
+      const size = props.size ?? "md";
+      const base: React.CSSProperties = {
+        padding: size === "sm" ? "4px 10px" : "6px 12px",
+        borderRadius: 8,
+        fontSize: size === "sm" ? 12 : 13,
+        fontWeight: 500,
+        cursor: props.disabled ? "not-allowed" : "pointer",
+        border: "1px solid transparent",
+        transition: "background 0.15s",
+        opacity: props.disabled ? 0.5 : 1,
+      };
+      const variants: Record<string, React.CSSProperties> = {
+        primary: {
+          background: "var(--accent)",
+          color: "var(--accent-fg)",
+        },
+        secondary: {
+          background: "var(--surface-muted)",
+          color: "var(--text)",
+          borderColor: "var(--border)",
+        },
+        ghost: {
+          background: "transparent",
+          color: "var(--text)",
+        },
+      };
+      return (
+        <button
+          type="button"
+          disabled={props.disabled ?? false}
+          onClick={() => emit("press")}
+          style={{ ...base, ...variants[variant] }}
+        >
+          {props.label}
+        </button>
+      );
+    },
+
+    TextInput: ({ props, bindings }) => {
+      const [value, setValue] = useBoundProp<string>(
+        (props.value ?? "") as string,
+        bindings?.value,
+      );
+      return (
+        <input
+          type="text"
+          value={value ?? ""}
+          placeholder={props.placeholder ?? ""}
+          onChange={(e) => setValue(e.target.value)}
+          style={{
+            padding: "6px 10px",
+            borderRadius: 8,
+            border: "1px solid var(--border)",
+            background: "var(--surface)",
+            color: "var(--text)",
+            fontSize: 13,
+            outline: "none",
+            width: "100%",
+          }}
+        />
+      );
+    },
+
+    Checkbox: ({ props, bindings }) => {
+      const [checked, setChecked] = useBoundProp<boolean>(
+        props.checked ?? false,
+        bindings?.checked,
+      );
+      return (
+        <label
+          style={{
+            display: "inline-flex",
+            alignItems: "center",
+            gap: 8,
+            fontSize: 13,
+            cursor: "pointer",
+          }}
+        >
+          <input
+            type="checkbox"
+            checked={checked ?? false}
+            onChange={(e) => setChecked(e.target.checked)}
+            style={{ accentColor: "var(--accent)" }}
+          />
+          {props.label && <span>{props.label}</span>}
+        </label>
+      );
+    },
+
+    ProgressBar: ({ props }) => {
+      const max = props.max ?? 100;
+      const value = Math.max(0, Math.min(max, props.value));
+      const pct = (value / max) * 100;
+      const color =
+        props.tone === "success"
+          ? "var(--success)"
+          : props.tone === "warn"
+            ? "var(--warn)"
+            : props.tone === "accent"
+              ? "var(--accent)"
+              : "var(--text-muted)";
+      return (
+        <div
+          style={{
+            width: "100%",
+            height: 6,
+            background: "var(--surface-muted)",
+            borderRadius: 999,
+            overflow: "hidden",
+          }}
+        >
+          <div
+            style={{
+              width: `${pct}%`,
+              height: "100%",
+              background: color,
+              transition: "width 0.3s",
+            }}
+          />
+        </div>
+      );
+    },
+
+    Callout: ({ props }) => {
+      const tone = props.tone ?? "info";
+      const toneBg = {
+        info: "color-mix(in oklab, var(--accent) 10%, transparent)",
+        success: "color-mix(in oklab, var(--success) 10%, transparent)",
+        warn: "color-mix(in oklab, var(--warn) 12%, transparent)",
+        tip: "color-mix(in oklab, var(--accent) 8%, transparent)",
+      } as const;
+      const toneBorder = {
+        info: "color-mix(in oklab, var(--accent) 30%, var(--border))",
+        success: "color-mix(in oklab, var(--success) 30%, var(--border))",
+        warn: "color-mix(in oklab, var(--warn) 35%, var(--border))",
+        tip: "color-mix(in oklab, var(--accent) 25%, var(--border))",
+      } as const;
+      return (
+        <div
+          style={{
+            padding: 12,
+            borderRadius: 10,
+            border: `1px solid ${toneBorder[tone]}`,
+            background: toneBg[tone],
+            fontSize: 13,
+            lineHeight: 1.5,
+          }}
+        >
+          {props.title && (
+            <div style={{ fontWeight: 600, marginBottom: 2 }}>
+              {props.title}
+            </div>
+          )}
+          <div>{props.text}</div>
+        </div>
+      );
+    },
+
+    // List is an unstyled flex-column container on purpose: when repeated
+    // children are interactive (Row with Checkbox + Button), a framed
+    // container looks like "a card in a card". ListItem below paints its
+    // own subtle top border between rows to keep a clear separator.
+    List: ({ children }) => (
+      <div
+        style={{
+          display: "flex",
+          flexDirection: "column",
+        }}
+      >
+        {children}
+      </div>
+    ),
+
+    ListItem: ({ props }) => (
+      <div
+        className="jr-list-item"
+        style={{
+          padding: "8px 0",
+          display: "flex",
+          alignItems: "center",
+          justifyContent: "space-between",
+          gap: 12,
+        }}
+      >
+        <div style={{ display: "flex", flexDirection: "column", gap: 2 }}>
+          <div style={{ fontSize: 13, fontWeight: 500 }}>{props.title}</div>
+          {props.description && (
+            <div style={{ fontSize: 12, color: "var(--text-muted)" }}>
+              {props.description}
+            </div>
+          )}
+        </div>
+        {props.meta && (
+          <div
+            style={{
+              fontSize: 12,
+              color: "var(--text-muted)",
+              whiteSpace: "nowrap",
+            }}
+          >
+            {props.meta}
+          </div>
+        )}
+      </div>
+    ),
+
+    Avatar: ({ props }) => {
+      const tones = {
+        default: { bg: "var(--surface-muted)", fg: "var(--text)" },
+        accent: {
+          bg: "color-mix(in oklab, var(--accent) 20%, transparent)",
+          fg: "var(--accent)",
+        },
+        success: {
+          bg: "color-mix(in oklab, var(--success) 20%, transparent)",
+          fg: "var(--success)",
+        },
+        warn: {
+          bg: "color-mix(in oklab, var(--warn) 20%, transparent)",
+          fg: "var(--warn)",
+        },
+      } as const;
+      const t = tones[props.tone ?? "default"];
+      return (
+        <span
+          style={{
+            display: "inline-flex",
+            alignItems: "center",
+            justifyContent: "center",
+            width: 32,
+            height: 32,
+            borderRadius: 999,
+            background: t.bg,
+            color: t.fg,
+            fontSize: 12,
+            fontWeight: 600,
+          }}
+        >
+          {props.initials.slice(0, 2).toUpperCase()}
+        </span>
+      );
+    },
+  },
+});

examples/devtools/next.config.ts

@@ -0,0 +1,7 @@
+import type { NextConfig } from "next";
+
+const nextConfig: NextConfig = {
+  allowedDevOrigins: ["devtools-demo.json-render.localhost"],
+};
+
+export default nextConfig;

examples/devtools/package.json

@@ -0,0 +1,35 @@
+{
+  "name": "example-devtools",
+  "version": "0.17.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "predev": "command -v portless >/dev/null 2>&1 || (echo '\\nportless is required but not installed. Run: npm i -g portless\\nSee: https://github.com/vercel-labs/portless\\n' && exit 1)",
+    "dev": "portless devtools-demo.json-render next dev --turbopack",
+    "build": "next build",
+    "start": "next start",
+    "lint": "eslint --max-warnings 0",
+    "check-types": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@ai-sdk/gateway": "^3.0.104",
+    "@ai-sdk/react": "^3.0.170",
+    "@json-render/core": "workspace:*",
+    "@json-render/devtools": "workspace:*",
+    "@json-render/devtools-react": "workspace:*",
+    "@json-render/react": "workspace:*",
+    "ai": "^6.0.168",
+    "next": "^16.2.4",
+    "react": "^19.2.4",
+    "react-dom": "^19.2.4",
+    "zod": "4.3.6"
+  },
+  "devDependencies": {
+    "@internal/eslint-config": "workspace:*",
+    "@types/node": "^22.10.0",
+    "@types/react": "^19.2.3",
+    "@types/react-dom": "^19.2.3",
+    "eslint": "^9.39.1",
+    "typescript": "^5.7.2"
+  }
+}

examples/devtools/tsconfig.json

@@ -0,0 +1,43 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": [
+      "ES2022",
+      "DOM",
+      "DOM.Iterable"
+    ],
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "allowJs": false,
+    "jsx": "react-jsx",
+    "strict": true,
+    "noUnusedLocals": false,
+    "noUnusedParameters": false,
+    "isolatedModules": true,
+    "esModuleInterop": true,
+    "resolveJsonModule": true,
+    "skipLibCheck": true,
+    "incremental": true,
+    "noEmit": true,
+    "plugins": [
+      {
+        "name": "next"
+      }
+    ],
+    "paths": {
+      "@/*": [
+        "./*"
+      ]
+    }
+  },
+  "include": [
+    "next-env.d.ts",
+    "**/*.ts",
+    "**/*.tsx",
+    ".next/types/**/*.ts",
+    ".next/dev/types/**/*.ts"
+  ],
+  "exclude": [
+    "node_modules"
+  ]
+}

examples/game-engine/CHANGELOG.md

@@ -1,5 +1,15 @@
 # example-game-engine
 
+## 0.1.2
+
+### Patch Changes
+
+- Updated dependencies [519a538]
+  - @json-render/core@0.16.0
+  - @json-render/react@0.16.0
+  - @json-render/react-three-fiber@0.16.0
+  - @json-render/yaml@0.16.0
+
 ## 0.1.1
 
 ### Patch Changes

examples/game-engine/README.md

@@ -0,0 +1,58 @@
+# Game Engine Example
+
+A 3D scene editor and lightweight game runtime built with json-render, React Three Fiber, and Rapier physics. Edit levels as structured objects, preview them on a canvas, then press play for first/third-person movement, physics, health/damage, NPCs, and optional AI-assisted editing.
+
+## What it shows
+
+- **3D rendering with json-render** -- the editor's scene graph is converted to a json-render `Spec` via `sceneToSpec`, then rendered with `ThreeRenderer` and the `@json-render/react-three-fiber` registry.
+- **AI scene editing** -- type a prompt in the editor sidebar; the server streams YAML patches that are merged into the current spec, updating the 3D scene in real time.
+- **In-game AI** -- while playing, an AI agent can manipulate the scene by streaming JSONL function calls (`addObject`, `updateObjectTransform`, etc.).
+- **Play mode with physics** -- toggle between edit mode (gizmos, selection) and play mode (Rapier physics, first/third-person controls, health, damage zones, collectibles).
+- **NPC dialogue with optional TTS** -- `GameCharacter` components support AI-generated dialogue, with optional ElevenLabs text-to-speech.
+- **GLB uploads** -- upload custom 3D models and environments via Vercel Blob.
+
+## Setup
+
+```bash
+pnpm install          # from the monorepo root
+cd examples/game-engine
+cp .env.example .env
+```
+
+Set the required environment variables:
+
+| Variable | Required | Description |
+|----------|----------|-------------|
+| `AI_GATEWAY_API_KEY` | Yes | Vercel AI Gateway key |
+| `AI_GATEWAY_MODEL` | No | Defaults to `anthropic/claude-sonnet-4-6` |
+| `ELEVENLABS_API_KEY` | No | Enables text-to-speech for NPC dialogue |
+| `KV_REST_API_URL` | No | Upstash Redis URL for rate limiting |
+| `KV_REST_API_TOKEN` | No | Upstash Redis token |
+| `RATE_LIMIT_PER_MINUTE` | No | Defaults to `10` |
+| `RATE_LIMIT_PER_DAY` | No | Defaults to `100` |
+
+Model/environment uploads require Vercel Blob configuration when deployed.
+
+## Run
+
+```bash
+pnpm dev
+# http://game-engine-demo.json-render.localhost:1355
+```
+
+Requires global [`portless`](https://github.com/vercel-labs/portless). The `predev` script checks for it automatically.
+
+## Files
+
+- `app/page.tsx` -- mounts `GameEngine`
+- `components/game-engine.tsx` -- main shell: R3F canvas, sidebars, play/edit mode toggle, AI prompt integration
+- `components/game/` -- game primitives (`GameBox`, `GameSphere`, `Player`, `GameCharacter`, etc.) with physics and interactions
+- `components/editor/` -- editor UI: object inspector, scene tree, AI prompt sidebar, gizmo controls
+- `components/hud/` -- in-game HUD: health bar, crosshair, in-game AI prompt
+- `app/api/ai/route.ts` -- streams YAML scene edits from the model
+- `app/api/ai-game/route.ts` -- streams JSONL function calls for in-game AI manipulation
+- `app/api/character-responses/route.ts` -- generates NPC dialogue, optionally with TTS
+- `lib/catalog.ts` -- 3D component catalog (R3F base + game-specific primitives)
+- `lib/registry.tsx` -- maps catalog types to R3F and game components
+- `lib/store.ts` -- Zustand store for scenes, selection, play mode, health, undo/redo
+- `lib/scene-to-spec.ts` / `lib/spec-to-scene.ts` -- converts between the editor's scene graph and json-render specs

examples/game-engine/next-env.d.ts

@@ -1,6 +0,0 @@
-/// <reference types="next" />
-/// <reference types="next/image-types/global" />
-import "./.next/dev/types/routes.d.ts";
-
-// NOTE: This file should not be edited
-// see https://nextjs.org/docs/app/api-reference/config/typescript for more information.

examples/game-engine/package.json

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

examples/gsplat/app/GaussianSplatViewer.tsx

@@ -0,0 +1,421 @@
+"use client";
+
+import { useEffect, useRef, useState, type ReactNode } from "react";
+import * as SPLAT from "gsplat";
+
+type Vec3 = [number, number, number];
+
+interface SplatEntry {
+  src: string;
+  position?: Vec3;
+  rotation?: Vec3;
+  scale?: Vec3;
+  visible?: boolean;
+}
+
+interface ViewerProps {
+  width?: string;
+  height?: string;
+  backgroundColor?: string;
+  controls?: boolean;
+  autoRotate?: boolean;
+  autoRotateSpeed?: number;
+  cameraPosition?: Vec3 | null;
+  cameraTarget?: Vec3 | null;
+  fov?: number | null;
+  progressBarColor?: string;
+  progressTrackColor?: string;
+  progressTextColor?: string;
+  progressBackgroundColor?: string;
+  /** Custom loading indicator — overrides the default progress bar */
+  loadingIndicator?: ReactNode;
+  /** Splat file URLs to load */
+  splats?: SplatEntry[];
+  children?: ReactNode;
+}
+
+interface ProgressIndicatorProps {
+  progress: number;
+  backgroundColor?: string;
+  textColor?: string;
+  barColor?: string;
+  trackColor?: string;
+}
+
+function ProgressIndicator({
+  progress,
+  backgroundColor = "#0a0a0a",
+  textColor = "#666",
+  barColor = "#fff",
+  trackColor = "#1e1e1e",
+}: ProgressIndicatorProps) {
+  const pct = Math.round(progress * 100);
+  return (
+    <div
+      style={{
+        position: "absolute",
+        inset: 0,
+        display: "flex",
+        flexDirection: "column",
+        alignItems: "center",
+        justifyContent: "center",
+        background: backgroundColor,
+        gap: 12,
+      }}
+    >
+      <span
+        aria-live="polite"
+        style={{
+          color: textColor,
+          fontFamily: "ui-monospace, monospace",
+          fontSize: 13,
+          letterSpacing: "0.04em",
+        }}
+      >
+        Loading splat... {pct}%
+      </span>
+      <div
+        role="progressbar"
+        aria-valuenow={pct}
+        aria-valuemin={0}
+        aria-valuemax={100}
+        aria-label="Loading progress"
+        style={{
+          width: 200,
+          height: 2,
+          background: trackColor,
+          borderRadius: 1,
+          overflow: "hidden",
+        }}
+      >
+        <div
+          style={{
+            width: `${pct}%`,
+            height: "100%",
+            background: barColor,
+            borderRadius: 1,
+            transition: "width 150ms ease-out",
+          }}
+        />
+      </div>
+    </div>
+  );
+}
+
+/** Convert a vertical FOV (degrees) to a focal length given a canvas height. */
+function fovToFocalLength(fovDeg: number, height: number): number {
+  return height / (2 * Math.tan((fovDeg * Math.PI) / 360));
+}
+
+/** Convert euler angles (degrees, XYZ order) to a Quaternion. */
+function eulerToQuaternion(euler: Vec3): SPLAT.Quaternion {
+  const [ex, ey, ez] = euler.map((d) => (d * Math.PI) / 180) as [
+    number,
+    number,
+    number,
+  ];
+  const cx = Math.cos(ex / 2),
+    sx = Math.sin(ex / 2);
+  const cy = Math.cos(ey / 2),
+    sy = Math.sin(ey / 2);
+  const cz = Math.cos(ez / 2),
+    sz = Math.sin(ez / 2);
+  return new SPLAT.Quaternion(
+    sx * cy * cz + cx * sy * sz,
+    cx * sy * cz - sx * cy * sz,
+    cx * cy * sz + sx * sy * cz,
+    cx * cy * cz - sx * sy * sz,
+  );
+}
+
+/**
+ * Container that manages a WebGL canvas and loads gaussian splats
+ * using Hugging Face's gsplat.js — a standalone WebGL renderer (no Three.js).
+ *
+ * This is an experimental demo component, kept inline in the example app.
+ */
+export function GaussianSplatViewer({
+  width = "100%",
+  height = "100%",
+  backgroundColor = "#000000",
+  controls: enableControls = true,
+  autoRotate = false,
+  autoRotateSpeed = 1,
+  cameraPosition = null,
+  cameraTarget = null,
+  fov = null,
+  progressBarColor,
+  progressTrackColor,
+  progressTextColor,
+  progressBackgroundColor,
+  children,
+  loadingIndicator,
+  splats,
+}: ViewerProps) {
+  const containerRef = useRef<HTMLDivElement>(null);
+  const cleanupRef = useRef<(() => void) | null>(null);
+  const [isLoading, setIsLoading] = useState(true);
+  const [progress, setProgress] = useState(0);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    if (!containerRef.current) return;
+
+    const container = containerRef.current;
+    let cancelled = false;
+
+    async function init() {
+      try {
+        // Clean up previous viewer
+        if (cleanupRef.current) {
+          cleanupRef.current();
+          cleanupRef.current = null;
+        }
+
+        const scene = new SPLAT.Scene();
+        const camera = new SPLAT.Camera();
+        const renderer = new SPLAT.WebGLRenderer();
+
+        // Apply camera position
+        if (cameraPosition) {
+          camera.position = new SPLAT.Vector3(
+            cameraPosition[0],
+            cameraPosition[1],
+            cameraPosition[2],
+          );
+        }
+
+        // Apply FOV by converting to focal length
+        const rect = container.getBoundingClientRect();
+        if (fov) {
+          const fl = fovToFocalLength(fov, rect.height);
+          camera.data.fx = fl;
+          camera.data.fy = fl;
+        }
+
+        // Size the canvas to the container
+        renderer.setSize(rect.width, rect.height);
+
+        // Style and append the canvas — absolute positioning prevents overflow
+        renderer.canvas.style.position = "absolute";
+        renderer.canvas.style.top = "0";
+        renderer.canvas.style.left = "0";
+        renderer.canvas.style.width = "100%";
+        renderer.canvas.style.height = "100%";
+        renderer.canvas.style.display = "block";
+        container.appendChild(renderer.canvas);
+
+        // Only create orbit controls if enabled
+        let controls: SPLAT.OrbitControls | null = null;
+        if (enableControls) {
+          controls = new SPLAT.OrbitControls(camera, renderer.canvas);
+
+          // Apply camera target (look-at)
+          if (cameraTarget) {
+            controls.setCameraTarget(
+              new SPLAT.Vector3(
+                cameraTarget[0],
+                cameraTarget[1],
+                cameraTarget[2],
+              ),
+            );
+          }
+        }
+
+        // Handle resize (debounced to avoid layout thrashing)
+        let resizeTimer: ReturnType<typeof setTimeout>;
+        const onResize = () => {
+          clearTimeout(resizeTimer);
+          resizeTimer = setTimeout(() => {
+            const r = container.getBoundingClientRect();
+            renderer.setSize(r.width, r.height);
+            // Update focal length on resize to maintain FOV
+            if (fov) {
+              const fl = fovToFocalLength(fov, r.height);
+              camera.data.fx = fl;
+              camera.data.fy = fl;
+            }
+          }, 100);
+        };
+        window.addEventListener("resize", onResize);
+
+        // Load splat files with progress tracking
+        if (splats && splats.length > 0) {
+          const totalSplats = splats.length;
+          for (let i = 0; i < totalSplats; i++) {
+            if (cancelled) return;
+            const entry = splats[i]!;
+            const splatObject = await SPLAT.Loader.LoadAsync(
+              entry.src,
+              scene,
+              (p: number) => {
+                if (!cancelled) {
+                  const overallProgress = (i + p) / totalSplats;
+                  // Use Math.max to prevent progress bar from jumping backwards
+                  setProgress((prev) => Math.max(prev, overallProgress));
+                }
+              },
+            );
+
+            // Apply per-splat transforms
+            if (entry.position) {
+              splatObject.position = new SPLAT.Vector3(
+                entry.position[0],
+                entry.position[1],
+                entry.position[2],
+              );
+            }
+            if (entry.rotation) {
+              splatObject.rotation = eulerToQuaternion(entry.rotation);
+            }
+            if (entry.scale) {
+              splatObject.scale = new SPLAT.Vector3(
+                entry.scale[0],
+                entry.scale[1],
+                entry.scale[2],
+              );
+            }
+            if (entry.visible !== undefined) {
+              splatObject.visible = entry.visible;
+            }
+          }
+        }
+
+        if (cancelled) {
+          controls?.dispose();
+          renderer.dispose();
+          if (renderer.canvas.parentElement) {
+            renderer.canvas.parentElement.removeChild(renderer.canvas);
+          }
+          window.removeEventListener("resize", onResize);
+          return;
+        }
+
+        setIsLoading(false);
+        setError(null);
+
+        // Render loop with optional auto-rotation
+        let animationId: number;
+        let lastTime = performance.now();
+        const frame = () => {
+          const now = performance.now();
+          const dt = (now - lastTime) / 1000;
+          lastTime = now;
+
+          if (autoRotate) {
+            // Rotate the camera around the camera target (not world origin)
+            const speed = autoRotateSpeed * 0.5;
+            const angle = speed * dt;
+            const pos = camera.position;
+            const target = cameraTarget
+              ? new SPLAT.Vector3(
+                  cameraTarget[0],
+                  cameraTarget[1],
+                  cameraTarget[2],
+                )
+              : new SPLAT.Vector3(0, 0, 0);
+            const dx = pos.x - target.x;
+            const dz = pos.z - target.z;
+            const cos = Math.cos(angle);
+            const sin = Math.sin(angle);
+            camera.position = new SPLAT.Vector3(
+              target.x + dx * cos - dz * sin,
+              pos.y,
+              target.z + dx * sin + dz * cos,
+            );
+          }
+
+          controls?.update();
+          renderer.render(scene, camera);
+          animationId = requestAnimationFrame(frame);
+        };
+        animationId = requestAnimationFrame(frame);
+
+        // Store cleanup function
+        cleanupRef.current = () => {
+          cancelAnimationFrame(animationId);
+          clearTimeout(resizeTimer);
+          window.removeEventListener("resize", onResize);
+          controls?.dispose();
+          renderer.dispose();
+          if (renderer.canvas.parentElement) {
+            renderer.canvas.parentElement.removeChild(renderer.canvas);
+          }
+        };
+      } catch (err) {
+        if (!cancelled) {
+          setError(
+            err instanceof Error ? err.message : "Failed to initialize viewer",
+          );
+          setIsLoading(false);
+        }
+      }
+    }
+
+    init();
+
+    return () => {
+      cancelled = true;
+      if (cleanupRef.current) {
+        cleanupRef.current();
+        cleanupRef.current = null;
+      }
+    };
+  }, [
+    splats,
+    enableControls,
+    autoRotate,
+    autoRotateSpeed,
+    cameraPosition,
+    cameraTarget,
+    fov,
+  ]);
+
+  return (
+    <div
+      style={{
+        width,
+        height,
+        position: "relative",
+        overflow: "hidden",
+        background: backgroundColor,
+      }}
+    >
+      <div
+        ref={containerRef}
+        style={{ position: "relative", width: "100%", height: "100%" }}
+      />
+      {isLoading &&
+        (loadingIndicator ?? (
+          <ProgressIndicator
+            progress={progress}
+            backgroundColor={progressBackgroundColor}
+            barColor={progressBarColor}
+            trackColor={progressTrackColor}
+            textColor={progressTextColor}
+          />
+        ))}
+      {error && (
+        <div
+          role="alert"
+          style={{
+            position: "absolute",
+            inset: 0,
+            display: "flex",
+            alignItems: "center",
+            justifyContent: "center",
+            background: backgroundColor,
+            color: "#ff4444",
+            fontFamily: "ui-monospace, monospace",
+            fontSize: 12,
+            padding: 20,
+            textAlign: "center",
+          }}
+        >
+          {error}
+        </div>
+      )}
+      {children}
+    </div>
+  );
+}

examples/gsplat/app/gsplat.d.ts

@@ -0,0 +1,79 @@
+declare module "gsplat" {
+  export class Vector3 {
+    constructor(x?: number, y?: number, z?: number);
+    x: number;
+    y: number;
+    z: number;
+  }
+
+  export class Quaternion {
+    constructor(x?: number, y?: number, z?: number, w?: number);
+    x: number;
+    y: number;
+    z: number;
+    w: number;
+  }
+
+  export class Splat {
+    get position(): Vector3;
+    set position(position: Vector3);
+    get rotation(): Quaternion;
+    set rotation(rotation: Quaternion);
+    get scale(): Vector3;
+    set scale(scale: Vector3);
+    get visible(): boolean;
+    set visible(visible: boolean);
+  }
+
+  export class Scene {
+    constructor();
+  }
+
+  export class Camera {
+    constructor();
+    get position(): Vector3;
+    set position(position: Vector3);
+    get rotation(): Quaternion;
+    set rotation(rotation: Quaternion);
+    data: CameraData;
+  }
+
+  export class CameraData {
+    get fx(): number;
+    set fx(fx: number);
+    get fy(): number;
+    set fy(fy: number);
+  }
+
+  export class WebGLRenderer {
+    constructor(canvas?: HTMLCanvasElement);
+    canvas: HTMLCanvasElement;
+    setSize(width: number, height: number): void;
+    render(scene: Scene, camera: Camera): void;
+    dispose(): void;
+  }
+
+  export class OrbitControls {
+    constructor(camera: Camera, canvas: HTMLCanvasElement);
+    setCameraTarget(target: Vector3): void;
+    minAngle: number;
+    maxAngle: number;
+    minZoom: number;
+    maxZoom: number;
+    orbitSpeed: number;
+    panSpeed: number;
+    zoomSpeed: number;
+    dampening: number;
+    update(): void;
+    dispose(): void;
+  }
+
+  export class Loader {
+    static LoadAsync(
+      url: string,
+      scene: Scene,
+      onProgress?: (progress: number) => void,
+      useCache?: boolean,
+    ): Promise<Splat>;
+  }
+}

examples/gsplat/app/layout.tsx

@@ -0,0 +1,21 @@
+import type { Metadata } from "next";
+
+export const metadata: Metadata = {
+  title: "json-render Gaussian Splatting Example",
+  description:
+    "Experimental gaussian splat viewer demo using gsplat.js (no Three.js)",
+};
+
+export default function RootLayout({
+  children,
+}: {
+  children: React.ReactNode;
+}) {
+  return (
+    <html lang="en">
+      <body style={{ margin: 0, fontFamily: "system-ui, sans-serif" }}>
+        {children}
+      </body>
+    </html>
+  );
+}

examples/gsplat/app/page.tsx

@@ -0,0 +1,460 @@
+"use client";
+
+import {
+  useCallback,
+  useEffect,
+  useRef,
+  useState,
+  useSyncExternalStore,
+} from "react";
+import { GaussianSplatViewer } from "./GaussianSplatViewer";
+import { scenes } from "./scenes";
+
+function highlightJson(json: string): string {
+  return json.replace(
+    /("(?:\\.|[^"\\])*")\s*(:)|("(?:\\.|[^"\\])*")|([-+]?\d+(?:\.\d+)?(?:[eE][+-]?\d+)?)|(\btrue\b|\bfalse\b|\bnull\b)|([{}[\]:,])/g,
+    (_, key, colon, str, num, lit, punct) => {
+      if (key) return `<span style="color:#FF4D8D">${key}</span>${colon}`;
+      if (str) return `<span style="color:#00CA50">${str}</span>`;
+      if (num) return `<span style="color:#47A8FF">${num}</span>`;
+      if (lit) return `<span style="color:#47A8FF">${lit}</span>`;
+      if (punct) return `<span style="color:#666">${punct}</span>`;
+      return _;
+    },
+  );
+}
+
+const MOBILE_BREAKPOINT = 768;
+
+function subscribeToResize(cb: () => void) {
+  window.addEventListener("resize", cb);
+  return () => window.removeEventListener("resize", cb);
+}
+
+function getIsMobile() {
+  return typeof window !== "undefined"
+    ? window.innerWidth < MOBILE_BREAKPOINT
+    : false;
+}
+
+function useIsMobile() {
+  return useSyncExternalStore(subscribeToResize, getIsMobile, () => false);
+}
+
+const LIST_WIDTH = 220;
+const JSON_WIDTH = 380;
+const HEADER_HEIGHT = 40;
+
+const headerStyle: React.CSSProperties = {
+  height: HEADER_HEIGHT,
+  display: "flex",
+  alignItems: "center",
+  padding: "0 16px",
+  fontSize: 11,
+  fontWeight: 600,
+  color: "#555",
+  letterSpacing: "0.08em",
+  textTransform: "uppercase",
+  fontFamily: "ui-monospace, monospace",
+  borderBottom: "1px solid #1e1e1e",
+  flexShrink: 0,
+  whiteSpace: "nowrap",
+  overflow: "hidden",
+  textOverflow: "ellipsis",
+  boxSizing: "border-box",
+};
+
+function SplatViewer({ sceneIndex }: { sceneIndex: number }) {
+  const scene = scenes[sceneIndex]!;
+  const v = scene.viewer;
+
+  return (
+    <GaussianSplatViewer
+      width="100%"
+      height="100%"
+      backgroundColor={v.backgroundColor ?? "#0a0a0a"}
+      controls={v.controls ?? true}
+      autoRotate={v.autoRotate ?? true}
+      autoRotateSpeed={v.autoRotateSpeed ?? 0.5}
+      cameraPosition={v.cameraPosition ?? [0, 2, 5]}
+      cameraTarget={v.cameraTarget ?? [0, 0, 0]}
+      fov={v.fov ?? 50}
+      splats={scene.splats}
+    />
+  );
+}
+
+function SceneListItem({
+  scene,
+  index,
+  isSelected,
+  onSelect,
+}: {
+  scene: (typeof scenes)[number];
+  index: number;
+  isSelected: boolean;
+  onSelect: (i: number) => void;
+}) {
+  return (
+    <button
+      role="option"
+      aria-selected={isSelected}
+      onClick={() => onSelect(index)}
+      style={{
+        display: "block",
+        width: "100%",
+        padding: "8px 16px",
+        fontSize: 13,
+        border: "none",
+        textAlign: "left",
+        background: isSelected ? "rgba(255,255,255,0.08)" : "transparent",
+        color: isSelected ? "#fff" : "#888",
+        fontWeight: isSelected ? 500 : 400,
+        cursor: "pointer",
+        borderLeft: isSelected ? "2px solid #fff" : "2px solid transparent",
+        fontFamily: "inherit",
+      }}
+    >
+      {scene.name}
+    </button>
+  );
+}
+
+function DesktopLayout() {
+  const [selectedIndex, setSelectedIndex] = useState(0);
+  const selected = scenes[selectedIndex]!;
+
+  return (
+    <div style={{ height: "100dvh", display: "flex", background: "#0a0a0a" }}>
+      <nav
+        aria-label="Splat scenes"
+        style={{
+          width: LIST_WIDTH,
+          flexShrink: 0,
+          display: "flex",
+          flexDirection: "column",
+          borderRight: "1px solid #1e1e1e",
+          background: "#0f0f0f",
+        }}
+      >
+        <div style={headerStyle}>Splat Scenes</div>
+        <div
+          role="listbox"
+          aria-label="Scene list"
+          style={{ flex: 1, overflowY: "auto", padding: "6px 0" }}
+        >
+          {scenes.map((scene, i) => (
+            <SceneListItem
+              key={scene.name}
+              scene={scene}
+              index={i}
+              isSelected={i === selectedIndex}
+              onSelect={setSelectedIndex}
+            />
+          ))}
+        </div>
+      </nav>
+
+      <main
+        style={{
+          flex: 1,
+          display: "flex",
+          flexDirection: "column",
+          minWidth: 0,
+        }}
+      >
+        <div style={headerStyle}>{selected.description}</div>
+        <div style={{ flex: 1, background: "#000", position: "relative" }}>
+          <SplatViewer key={selectedIndex} sceneIndex={selectedIndex} />
+        </div>
+      </main>
+
+      <aside
+        aria-label="Spec JSON"
+        style={{
+          width: JSON_WIDTH,
+          flexShrink: 0,
+          display: "flex",
+          flexDirection: "column",
+          borderLeft: "1px solid #1e1e1e",
+          background: "#0d0d0d",
+        }}
+      >
+        <div style={headerStyle}>Spec JSON</div>
+        <pre
+          style={{
+            flex: 1,
+            margin: 0,
+            padding: 14,
+            overflowY: "auto",
+            overflowX: "auto",
+            fontSize: 11,
+            lineHeight: 1.6,
+            fontFamily:
+              "ui-monospace, 'Cascadia Code', 'Source Code Pro', Menlo, Consolas, monospace",
+            color: "#EDEDED",
+            tabSize: 2,
+          }}
+          dangerouslySetInnerHTML={{
+            __html: highlightJson(
+              JSON.stringify(
+                { spec: selected.spec, splats: selected.splats },
+                null,
+                2,
+              ),
+            ),
+          }}
+        />
+      </aside>
+    </div>
+  );
+}
+
+function MobileLayout() {
+  const [selectedIndex, setSelectedIndex] = useState(0);
+  const [showJson, setShowJson] = useState(false);
+  const [showScenes, setShowScenes] = useState(false);
+  const selected = scenes[selectedIndex]!;
+  const scenePanelRef = useRef<HTMLDivElement>(null);
+  const jsonPanelRef = useRef<HTMLDivElement>(null);
+
+  const closeScenes = useCallback(() => setShowScenes(false), []);
+  const closeJson = useCallback(() => setShowJson(false), []);
+
+  // Close overlays on Escape
+  useEffect(() => {
+    const onKeyDown = (e: KeyboardEvent) => {
+      if (e.key === "Escape") {
+        if (showScenes) closeScenes();
+        if (showJson) closeJson();
+      }
+    };
+    window.addEventListener("keydown", onKeyDown);
+    return () => window.removeEventListener("keydown", onKeyDown);
+  }, [showScenes, showJson, closeScenes, closeJson]);
+
+  // Focus the panel when it opens
+  useEffect(() => {
+    if (showScenes) scenePanelRef.current?.focus();
+  }, [showScenes]);
+  useEffect(() => {
+    if (showJson) jsonPanelRef.current?.focus();
+  }, [showJson]);
+
+  return (
+    <div
+      style={{
+        height: "100dvh",
+        display: "flex",
+        flexDirection: "column",
+        background: "#0a0a0a",
+        overflow: "hidden",
+      }}
+    >
+      <header
+        style={{
+          height: 48,
+          display: "flex",
+          alignItems: "center",
+          justifyContent: "space-between",
+          padding: "0 12px",
+          borderBottom: "1px solid #1e1e1e",
+          background: "#0f0f0f",
+          flexShrink: 0,
+          gap: 8,
+        }}
+      >
+        <button
+          aria-label={`Scene: ${selected.name}. Open scene list`}
+          aria-expanded={showScenes}
+          onClick={() => {
+            setShowScenes((v) => !v);
+            setShowJson(false);
+          }}
+          style={{
+            background: showScenes ? "rgba(255,255,255,0.1)" : "transparent",
+            border: "1px solid #333",
+            borderRadius: 6,
+            color: "#ccc",
+            fontSize: 12,
+            fontWeight: 500,
+            padding: "6px 10px",
+            cursor: "pointer",
+            fontFamily: "inherit",
+            whiteSpace: "nowrap",
+            overflow: "hidden",
+            textOverflow: "ellipsis",
+            maxWidth: "50%",
+          }}
+        >
+          {selected.name}
+        </button>
+
+        <span
+          style={{
+            flex: 1,
+            fontSize: 10,
+            color: "#555",
+            textAlign: "center",
+            overflow: "hidden",
+            textOverflow: "ellipsis",
+            whiteSpace: "nowrap",
+            fontFamily: "ui-monospace, monospace",
+            textTransform: "uppercase",
+            letterSpacing: "0.06em",
+          }}
+        >
+          {selected.description}
+        </span>
+
+        <button
+          aria-label="Toggle JSON panel"
+          aria-expanded={showJson}
+          onClick={() => {
+            setShowJson((v) => !v);
+            setShowScenes(false);
+          }}
+          style={{
+            background: showJson ? "rgba(255,255,255,0.1)" : "transparent",
+            border: "1px solid #333",
+            borderRadius: 6,
+            color: "#ccc",
+            fontSize: 11,
+            fontWeight: 500,
+            padding: "6px 10px",
+            cursor: "pointer",
+            fontFamily: "ui-monospace, monospace",
+            whiteSpace: "nowrap",
+            letterSpacing: "0.04em",
+          }}
+        >
+          JSON
+        </button>
+      </header>
+
+      <div style={{ flex: 1, position: "relative", minHeight: 0 }}>
+        <SplatViewer key={selectedIndex} sceneIndex={selectedIndex} />
+
+        {showScenes && (
+          <>
+            <div
+              onClick={closeScenes}
+              style={{
+                position: "absolute",
+                inset: 0,
+                background: "rgba(0,0,0,0.5)",
+                zIndex: 10,
+              }}
+            />
+            <div
+              ref={scenePanelRef}
+              role="dialog"
+              aria-modal="true"
+              aria-label="Scene list"
+              tabIndex={-1}
+              style={{
+                position: "absolute",
+                top: 0,
+                left: 0,
+                bottom: 0,
+                width: "75%",
+                maxWidth: 280,
+                background: "#0f0f0f",
+                borderRight: "1px solid #1e1e1e",
+                zIndex: 11,
+                display: "flex",
+                flexDirection: "column",
+                overflowY: "auto",
+              }}
+            >
+              <div style={{ ...headerStyle, height: 36 }}>Splat Scenes</div>
+              <div
+                role="listbox"
+                aria-label="Scene list"
+                style={{ padding: "6px 0" }}
+              >
+                {scenes.map((scene, i) => (
+                  <SceneListItem
+                    key={scene.name}
+                    scene={scene}
+                    index={i}
+                    isSelected={i === selectedIndex}
+                    onSelect={(idx) => {
+                      setSelectedIndex(idx);
+                      closeScenes();
+                    }}
+                  />
+                ))}
+              </div>
+            </div>
+          </>
+        )}
+
+        {showJson && (
+          <>
+            <div
+              onClick={closeJson}
+              style={{
+                position: "absolute",
+                inset: 0,
+                background: "rgba(0,0,0,0.5)",
+                zIndex: 10,
+              }}
+            />
+            <div
+              ref={jsonPanelRef}
+              role="dialog"
+              aria-modal="true"
+              aria-label="Spec JSON"
+              tabIndex={-1}
+              style={{
+                position: "absolute",
+                top: 0,
+                right: 0,
+                bottom: 0,
+                width: "85%",
+                maxWidth: 400,
+                background: "#0d0d0d",
+                borderLeft: "1px solid #1e1e1e",
+                zIndex: 11,
+                display: "flex",
+                flexDirection: "column",
+              }}
+            >
+              <div style={{ ...headerStyle, height: 36 }}>Spec JSON</div>
+              <pre
+                style={{
+                  flex: 1,
+                  margin: 0,
+                  padding: 14,
+                  overflowY: "auto",
+                  overflowX: "auto",
+                  fontSize: 11,
+                  lineHeight: 1.6,
+                  fontFamily:
+                    "ui-monospace, 'Cascadia Code', 'Source Code Pro', Menlo, Consolas, monospace",
+                  color: "#EDEDED",
+                  tabSize: 2,
+                }}
+                dangerouslySetInnerHTML={{
+                  __html: highlightJson(
+                    JSON.stringify(
+                      { spec: selected.spec, splats: selected.splats },
+                      null,
+                      2,
+                    ),
+                  ),
+                }}
+              />
+            </div>
+          </>
+        )}
+      </div>
+    </div>
+  );
+}
+
+export default function Page() {
+  const isMobile = useIsMobile();
+  return isMobile ? <MobileLayout /> : <DesktopLayout />;
+}

examples/gsplat/app/scenes/_helpers.ts

@@ -0,0 +1,24 @@
+export type ViewerConfig = {
+  backgroundColor?: string;
+  controls?: boolean;
+  autoRotate?: boolean;
+  autoRotateSpeed?: number;
+  cameraPosition?: [number, number, number];
+  cameraTarget?: [number, number, number];
+  fov?: number;
+};
+
+// The "spec" here is just JSON shown next to the viewer for illustration —
+// the example doesn't actually render specs, so we keep it as a plain object.
+export type Scene = {
+  name: string;
+  description: string;
+  spec: Record<string, unknown>;
+  viewer: ViewerConfig;
+  splats: Array<{
+    src: string;
+    position?: [number, number, number];
+    rotation?: [number, number, number];
+    scale?: [number, number, number];
+  }>;
+};

examples/gsplat/app/scenes/bicycle.ts

@@ -0,0 +1,41 @@
+import type { Scene } from "./_helpers";
+
+export const bicycle: Scene = {
+  name: "Bicycle",
+  description: "A bicycle scene captured with gaussian splatting",
+  spec: {
+    root: "viewer",
+    elements: {
+      viewer: {
+        type: "GaussianSplatViewer",
+        props: {
+          width: "100%",
+          height: "100vh",
+          backgroundColor: "#0a0a0a",
+          controls: true,
+          autoRotate: true,
+          autoRotateSpeed: 0.4,
+          cameraPosition: [3, 2, 5],
+          cameraTarget: [0, 0, 0],
+          fov: 55,
+        },
+        children: [],
+      },
+    },
+  },
+  viewer: {
+    backgroundColor: "#0a0a0a",
+    controls: true,
+    autoRotate: true,
+    autoRotateSpeed: 0.4,
+    cameraPosition: [3, 2, 5],
+    cameraTarget: [0, 0, 0],
+    fov: 55,
+  },
+  splats: [
+    {
+      src: "https://huggingface.co/datasets/dylanebert/3dgs/resolve/main/bicycle/bicycle-7k.splat",
+      position: [0, 0, 0],
+    },
+  ],
+};

examples/gsplat/app/scenes/bonsai.ts

@@ -0,0 +1,41 @@
+import type { Scene } from "./_helpers";
+
+export const bonsai: Scene = {
+  name: "Bonsai",
+  description: "A bonsai tree captured with gaussian splatting",
+  spec: {
+    root: "viewer",
+    elements: {
+      viewer: {
+        type: "GaussianSplatViewer",
+        props: {
+          width: "100%",
+          height: "100vh",
+          backgroundColor: "#0a0a0a",
+          controls: true,
+          autoRotate: true,
+          autoRotateSpeed: 0.5,
+          cameraPosition: [0, 1.5, 3],
+          cameraTarget: [0, 0.5, 0],
+          fov: 50,
+        },
+        children: [],
+      },
+    },
+  },
+  viewer: {
+    backgroundColor: "#0a0a0a",
+    controls: true,
+    autoRotate: true,
+    autoRotateSpeed: 0.5,
+    cameraPosition: [0, 1.5, 3],
+    cameraTarget: [0, 0.5, 0],
+    fov: 50,
+  },
+  splats: [
+    {
+      src: "https://huggingface.co/datasets/dylanebert/3dgs/resolve/main/bonsai/bonsai-7k.splat",
+      position: [0, 0, 0],
+    },
+  ],
+};

examples/gsplat/app/scenes/garden.ts

@@ -0,0 +1,41 @@
+import type { Scene } from "./_helpers";
+
+export const garden: Scene = {
+  name: "Garden",
+  description: "A garden scene captured with gaussian splatting",
+  spec: {
+    root: "viewer",
+    elements: {
+      viewer: {
+        type: "GaussianSplatViewer",
+        props: {
+          width: "100%",
+          height: "100vh",
+          backgroundColor: "#0a0a0a",
+          controls: true,
+          autoRotate: true,
+          autoRotateSpeed: 0.3,
+          cameraPosition: [2, 2, 5],
+          cameraTarget: [0, 0, 0],
+          fov: 60,
+        },
+        children: [],
+      },
+    },
+  },
+  viewer: {
+    backgroundColor: "#0a0a0a",
+    controls: true,
+    autoRotate: true,
+    autoRotateSpeed: 0.3,
+    cameraPosition: [2, 2, 5],
+    cameraTarget: [0, 0, 0],
+    fov: 60,
+  },
+  splats: [
+    {
+      src: "https://huggingface.co/datasets/dylanebert/3dgs/resolve/main/garden/garden-7k.splat",
+      position: [0, 0, 0],
+    },
+  ],
+};

examples/gsplat/app/scenes/index.ts

@@ -0,0 +1,17 @@
+import type { Scene } from "./_helpers";
+import { bonsai } from "./bonsai";
+import { garden } from "./garden";
+import { bicycle } from "./bicycle";
+import { kitchen } from "./kitchen";
+import { stump } from "./stump";
+import { multiOffset } from "./multi-offset";
+export type { Scene };
+
+export const scenes: Scene[] = [
+  bonsai,
+  garden,
+  bicycle,
+  kitchen,
+  stump,
+  multiOffset,
+];

examples/gsplat/app/scenes/kitchen.ts

@@ -0,0 +1,41 @@
+import type { Scene } from "./_helpers";
+
+export const kitchen: Scene = {
+  name: "Kitchen",
+  description: "An indoor kitchen scan showing spatial depth and lighting",
+  spec: {
+    root: "viewer",
+    elements: {
+      viewer: {
+        type: "GaussianSplatViewer",
+        props: {
+          width: "100%",
+          height: "100vh",
+          backgroundColor: "#0d0d0d",
+          controls: true,
+          autoRotate: true,
+          autoRotateSpeed: 0.3,
+          cameraPosition: [2, 2, 4],
+          cameraTarget: [0, 0.5, 0],
+          fov: 55,
+        },
+        children: [],
+      },
+    },
+  },
+  viewer: {
+    backgroundColor: "#0d0d0d",
+    controls: true,
+    autoRotate: true,
+    autoRotateSpeed: 0.3,
+    cameraPosition: [2, 2, 4],
+    cameraTarget: [0, 0.5, 0],
+    fov: 55,
+  },
+  splats: [
+    {
+      src: "https://huggingface.co/datasets/dylanebert/3dgs/resolve/main/kitchen/kitchen-7k.splat",
+      position: [0, 0, 0],
+    },
+  ],
+};

examples/gsplat/app/scenes/multi-offset.ts

@@ -0,0 +1,47 @@
+import type { Scene } from "./_helpers";
+
+export const multiOffset: Scene = {
+  name: "Multi-Splat (Offset)",
+  description:
+    "Two splats placed away from the origin — demonstrates off-center orbit",
+  spec: {
+    root: "viewer",
+    elements: {
+      viewer: {
+        type: "GaussianSplatViewer",
+        props: {
+          width: "100%",
+          height: "100vh",
+          backgroundColor: "#0a0a0a",
+          controls: true,
+          autoRotate: true,
+          autoRotateSpeed: 0.4,
+          cameraPosition: [5, 3, 8],
+          cameraTarget: [3, 0.5, 3],
+          fov: 50,
+        },
+        children: [],
+      },
+    },
+  },
+  viewer: {
+    backgroundColor: "#0a0a0a",
+    controls: true,
+    autoRotate: true,
+    autoRotateSpeed: 0.4,
+    cameraPosition: [5, 3, 8],
+    cameraTarget: [3, 0.5, 3],
+    fov: 50,
+  },
+  splats: [
+    {
+      src: "https://huggingface.co/datasets/dylanebert/3dgs/resolve/main/bonsai/bonsai-7k.splat",
+      position: [1.5, 0, 3],
+    },
+    {
+      src: "https://huggingface.co/datasets/dylanebert/3dgs/resolve/main/stump/stump-7k.splat",
+      position: [4.5, 0, 3],
+      scale: [0.8, 0.8, 0.8],
+    },
+  ],
+};

examples/gsplat/app/scenes/stump.ts

@@ -0,0 +1,41 @@
+import type { Scene } from "./_helpers";
+
+export const stump: Scene = {
+  name: "Stump",
+  description: "A tree stump with organic textures and natural detail",
+  spec: {
+    root: "viewer",
+    elements: {
+      viewer: {
+        type: "GaussianSplatViewer",
+        props: {
+          width: "100%",
+          height: "100vh",
+          backgroundColor: "#080808",
+          controls: true,
+          autoRotate: true,
+          autoRotateSpeed: 0.6,
+          cameraPosition: [1.5, 1.5, 3],
+          cameraTarget: [0, 0.3, 0],
+          fov: 45,
+        },
+        children: [],
+      },
+    },
+  },
+  viewer: {
+    backgroundColor: "#080808",
+    controls: true,
+    autoRotate: true,
+    autoRotateSpeed: 0.6,
+    cameraPosition: [1.5, 1.5, 3],
+    cameraTarget: [0, 0.3, 0],
+    fov: 45,
+  },
+  splats: [
+    {
+      src: "https://huggingface.co/datasets/dylanebert/3dgs/resolve/main/stump/stump-7k.splat",
+      position: [0, 0, 0],
+    },
+  ],
+};

examples/gsplat/eslint.config.js

@@ -0,0 +1,11 @@
+import { nextJsConfig } from "@internal/eslint-config/next-js";
+
+/** @type {import("eslint").Linter.Config[]} */
+export default [
+  ...nextJsConfig,
+  {
+    rules: {
+      "react/prop-types": "off",
+    },
+  },
+];

examples/gsplat/next.config.ts

@@ -0,0 +1,5 @@
+import type { NextConfig } from "next";
+
+const nextConfig: NextConfig = {};
+
+export default nextConfig;

examples/gsplat/package.json

@@ -0,0 +1,29 @@
+{
+  "name": "example-gsplat",
+  "version": "0.1.0",
+  "type": "module",
+  "private": true,
+  "scripts": {
+    "predev": "command -v portless >/dev/null 2>&1 || (echo '\\nportless is required but not installed. Run: npm i -g portless\\nSee: https://github.com/vercel-labs/portless\\n' && exit 1)",
+    "dev": "portless gsplat-demo.json-render next dev --turbopack",
+    "dev:local": "next dev --turbopack",
+    "build": "next build",
+    "start": "next start",
+    "lint": "eslint --max-warnings 0",
+    "check-types": "tsc --noEmit"
+  },
+  "dependencies": {
+    "gsplat": "^1.2.9",
+    "next": "16.1.6",
+    "react": "19.2.4",
+    "react-dom": "19.2.4"
+  },
+  "devDependencies": {
+    "@internal/eslint-config": "workspace:*",
+    "@types/node": "^22.10.0",
+    "@types/react": "19.2.3",
+    "@types/react-dom": "19.2.3",
+    "eslint": "^9.39.1",
+    "typescript": "^5.7.2"
+  }
+}

examples/gsplat/tsconfig.json

@@ -0,0 +1,13 @@
+{
+  "extends": "../../packages/typescript-config/nextjs.json",
+  "compilerOptions": {
+    "plugins": [{ "name": "next" }],
+    "declaration": false,
+    "declarationMap": false,
+    "paths": {
+      "@/*": ["./*"]
+    }
+  },
+  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
+  "exclude": ["node_modules"]
+}

examples/harness-chat/README.md

@@ -0,0 +1,78 @@
+# Harness Agent Chat Example
+
+**json-render as the UI for agent harnesses.**
+
+This example runs a real coding agent -- pick **Claude Code**, **Codex**, or **Pi** -- in a Vercel Sandbox, driven through the AI SDK 7 [`HarnessAgent`](https://vercel.com/changelog/program-agent-harnesses-with-ai-sdk) API, and renders its work as generative UI instead of a wall of markdown.
+
+The agent edits files, runs commands, and executes tests inside the sandbox. When it reports back, it emits a json-render spec constrained to a catalog of work-report components (`Steps`, `FileChange`, `Terminal`, `TestResults`, `Metric`, `BarChart`, `LineChart`, ...), which streams into the chat as structured, rendered UI.
+
+## How it works
+
+The round trip: the browser posts the chosen agent and prompt, the server streams a harness turn, and `pipeJsonRender` extracts the spec fence on the way back.
+
+```mermaid
+flowchart LR
+  subgraph browser [Browser]
+    UI["app/page.tsx<br/>useChat · AgentSelector"]
+  end
+  subgraph server ["app/api/agent/route.ts"]
+    SESS["getSession(chatId, agent)"]
+    AGENT["HarnessAgent<br/>Claude Code · Codex · Pi"]
+    SANDBOX[("Vercel Sandbox")]
+    PIPE["pipeJsonRender"]
+  end
+  UI -- "POST { messages, agent }" --> SESS
+  SESS --> AGENT
+  AGENT <-->|"bash · edit · test"| SANDBOX
+  AGENT -- "toUIMessageStream()" --> PIPE
+  PIPE -- "text · tool calls · data-spec parts" --> UI
+```
+
+What happens on a single turn:
+
+```mermaid
+sequenceDiagram
+  participant U as User
+  participant UI as page.tsx
+  participant API as /api/agent
+  participant AG as HarnessAgent
+  participant SB as Sandbox
+  U->>UI: pick agent + send prompt
+  UI->>API: POST { messages, agent }
+  API->>AG: getSession + stream(prompt)
+  AG->>SB: run commands / edit files
+  SB-->>AG: output
+  AG-->>API: prose + spec fence (streamed)
+  Note over API: pipeJsonRender splits the spec fence out
+  API-->>UI: text · tool calls · data-spec parts
+  UI-->>U: markdown + rendered report
+```
+
+1. `lib/agents.ts` is a client-safe catalog of the selectable agents; `lib/agent.ts` builds a `HarnessAgent` per agent (Claude Code, Codex, or Pi), each with a Vercel sandbox provider. The shared `instructions` embed `agentReportCatalog.prompt({ mode: "inline" })`, teaching the runtime to wrap its UI report in a ` ```spec ` fence.
+2. `app/api/agent/route.ts` reads the chosen `agent` from the request body and keeps one live harness session per chat, locked to the agent that created it (the harness owns its own conversation history, so each turn sends only the fresh user message). It streams the turn and pipes it through `pipeJsonRender` -- which extracts the spec fence into typed `data-spec` parts while passing text and tool calls through untouched.
+3. `app/page.tsx` renders text with markdown, builtin tool calls (bash, edit, ...) as activity lines, and the spec inline with `<ReportRenderer>` via `useJsonRenderMessage`. The `AgentSelector` on the first screen chooses which harness to run.
+
+Because `HarnessAgent.stream()` returns a standard AI SDK `StreamTextResult`, the json-render pipeline is identical to the single-model [chat example](../chat) -- swapping a model call for a full agent harness changes nothing about the UI layer.
+
+## Setup
+
+The AI SDK harness packages are **experimental canary releases**; expect breaking changes.
+
+1. Give the sandbox provider Vercel credentials, either:
+   - Be logged in with the Vercel CLI (`vercel login`) and run the dev server in a terminal (the SDK only falls back to CLI auth when attached to a TTY). It uses or creates a `vercel-sandbox-default-project` in your personal scope.
+   - Or link a project and pull an OIDC token: `vercel link && vercel env pull`.
+
+2. Provide model credentials. `AI_GATEWAY_API_KEY` (Vercel AI Gateway) works for all three agents. Or use a provider key directly for the agent you run: `ANTHROPIC_API_KEY` (Claude Code) or `OPENAI_API_KEY` (Codex); Pi resolves credentials from the gateway.
+
+3. Optionally pin a model per agent: `CLAUDE_CODE_MODEL`, `CODEX_MODEL`, or `PI_MODEL` (each defaults to that runtime's own default).
+
+## Run
+
+```bash
+pnpm install
+pnpm dev
+```
+
+Then open `harness-chat-demo.json-render.localhost:1355`.
+
+Note: the first message in a chat boots a fresh sandbox, which takes a while; follow-up messages reuse it. "Start Over" destroys the server-side session and its sandbox; idle sessions are destroyed after 10 minutes.

examples/harness-chat/app/api/agent/route.ts

@@ -0,0 +1,64 @@
+import {
+  createUIMessageStream,
+  createUIMessageStreamResponse,
+  type UIMessage,
+} from "ai";
+import { pipeJsonRender } from "@json-render/core";
+import { getSession, dropSession } from "@/lib/agent";
+import { DEFAULT_AGENT_ID, isAgentId } from "@/lib/agents";
+
+// Harness turns are long: the agent boots a sandbox, edits files, and runs
+// commands before answering.
+export const maxDuration = 600;
+
+function lastUserText(messages: UIMessage[]): string | null {
+  for (let i = messages.length - 1; i >= 0; i--) {
+    const message = messages[i];
+    if (message?.role !== "user") continue;
+    const text = message.parts
+      .filter((part) => part.type === "text")
+      .map((part) => part.text)
+      .join("\n")
+      .trim();
+    return text.length > 0 ? text : null;
+  }
+  return null;
+}
+
+export async function POST(req: Request) {
+  const body = await req.json();
+  const chatId: string = body.id ?? "default";
+  const messages: UIMessage[] = body.messages ?? [];
+
+  const prompt = lastUserText(messages);
+  if (!prompt) {
+    return new Response(
+      JSON.stringify({ error: "a user message with text is required" }),
+      { status: 400, headers: { "Content-Type": "application/json" } },
+    );
+  }
+
+  // The agent is chosen on the first message and locked for the chat: an
+  // existing session ignores `body.agent` and keeps its original agent.
+  const requestedAgent = isAgentId(body.agent) ? body.agent : DEFAULT_AGENT_ID;
+
+  // The harness session owns its own conversation history, so each turn
+  // sends only the fresh user input -- not the whole transcript.
+  const { session, agent } = await getSession(chatId, requestedAgent);
+  const result = await agent.stream({ prompt, session });
+
+  const stream = createUIMessageStream({
+    execute: async ({ writer }) => {
+      writer.merge(pipeJsonRender(result.toUIMessageStream()));
+    },
+  });
+
+  return createUIMessageStreamResponse({ stream });
+}
+
+export async function DELETE(req: Request) {
+  const { searchParams } = new URL(req.url);
+  const chatId = searchParams.get("id") ?? "default";
+  dropSession(chatId);
+  return new Response(null, { status: 204 });
+}

examples/harness-chat/app/globals.css

@@ -0,0 +1,161 @@
+@import "tailwindcss";
+@import "tw-animate-css";
+
+@source "../../../node_modules/streamdown/dist/*.js";
+
+@custom-variant dark (&:is(.dark *));
+
+@theme inline {
+  --radius-sm: calc(var(--radius) - 4px);
+  --radius-md: calc(var(--radius) - 2px);
+  --radius-lg: var(--radius);
+  --radius-xl: calc(var(--radius) + 4px);
+  --color-background: var(--background);
+  --color-foreground: var(--foreground);
+  --color-card: var(--card);
+  --color-card-foreground: var(--card-foreground);
+  --color-primary: var(--primary);
+  --color-primary-foreground: var(--primary-foreground);
+  --color-secondary: var(--secondary);
+  --color-secondary-foreground: var(--secondary-foreground);
+  --color-muted: var(--muted);
+  --color-muted-foreground: var(--muted-foreground);
+  --color-accent: var(--accent);
+  --color-accent-foreground: var(--accent-foreground);
+  --color-destructive: var(--destructive);
+  --color-border: var(--border);
+  --color-input: var(--input);
+  --color-ring: var(--ring);
+  --color-chart-1: var(--chart-1);
+  --color-chart-2: var(--chart-2);
+  --color-chart-3: var(--chart-3);
+  --color-chart-4: var(--chart-4);
+}
+
+:root {
+  --radius: 0.625rem;
+
+  /* Restrained neutrals. Craft comes from type and spacing, not color. */
+  --background: oklch(0.994 0 0);
+  --foreground: oklch(0.205 0 0);
+  --card: oklch(1 0 0);
+  --card-foreground: oklch(0.205 0 0);
+  --primary: oklch(0.205 0 0);
+  --primary-foreground: oklch(0.985 0 0);
+  --secondary: oklch(0.97 0 0);
+  --secondary-foreground: oklch(0.205 0 0);
+  --muted: oklch(0.973 0 0);
+  --muted-foreground: oklch(0.553 0 0);
+  --accent: oklch(0.968 0 0);
+  --accent-foreground: oklch(0.205 0 0);
+  --destructive: oklch(0.585 0.2 27.3);
+  --border: oklch(0.917 0 0);
+  --input: oklch(0.917 0 0);
+  --ring: oklch(0.708 0 0);
+
+  /* Muted, functional data colors — used only when a chart names a tone. */
+  --chart-1: oklch(0.5 0.13 277);
+  --chart-2: oklch(0.6 0.12 162);
+  --chart-3: oklch(0.7 0.12 70);
+  --chart-4: oklch(0.58 0.12 248);
+}
+
+.dark {
+  --background: oklch(0.165 0 0);
+  --foreground: oklch(0.985 0 0);
+  --card: oklch(0.205 0 0);
+  --card-foreground: oklch(0.985 0 0);
+  --primary: oklch(0.985 0 0);
+  --primary-foreground: oklch(0.205 0 0);
+  --secondary: oklch(0.265 0 0);
+  --secondary-foreground: oklch(0.985 0 0);
+  --muted: oklch(0.265 0 0);
+  --muted-foreground: oklch(0.708 0 0);
+  --accent: oklch(0.27 0 0);
+  --accent-foreground: oklch(0.985 0 0);
+  --destructive: oklch(0.704 0.191 22.2);
+  --border: oklch(1 0 0 / 9%);
+  --input: oklch(1 0 0 / 13%);
+  --ring: oklch(0.556 0 0);
+  --chart-1: oklch(0.62 0.13 277);
+  --chart-2: oklch(0.68 0.12 162);
+  --chart-3: oklch(0.76 0.12 70);
+  --chart-4: oklch(0.66 0.12 248);
+}
+
+@layer base {
+  * {
+    @apply border-border outline-ring/50;
+  }
+  body {
+    @apply bg-background text-foreground;
+  }
+}
+
+/* Map Tailwind's font tokens to Geist. next/font sets --font-geist-* on
+   <body>, so this must live on body (not :root, where those vars are
+   undefined) for `font-sans`/`font-mono` to resolve to Geist / Geist Mono. */
+body {
+  --font-sans: var(--font-geist-sans);
+  --font-mono: var(--font-geist-mono);
+}
+
+button {
+  cursor: pointer;
+}
+
+/* One restrained elevation step — a hairline, not a drop shadow. */
+.shadow-subtle {
+  box-shadow:
+    0 1px 1px oklch(0 0 0 / 0.04),
+    0 2px 6px -2px oklch(0 0 0 / 0.06);
+}
+
+/* Inline code in agent markdown gets a shaded pill. `:not(pre) > code` targets
+   only inline code, leaving fenced code blocks (Shiki) untouched. The tint is
+   derived from the muted-foreground so it reads in both light and dark mode. */
+.markdown :not(pre) > code {
+  border-radius: 0.375rem;
+  background-color: color-mix(in oklab, var(--muted-foreground) 16%, transparent);
+  padding: 0.1em 0.35em;
+  font-size: 0.85em;
+  font-family: var(--font-mono);
+}
+
+/* A bright band sweeps across dim text. `inline-block` is essential: it sizes
+   the gradient to the text itself, so the band actually passes over the words
+   (on a full-width block the band rarely reaches the short label). */
+@keyframes shimmer {
+  0% {
+    background-position: 100% 0;
+  }
+  100% {
+    background-position: 0% 0;
+  }
+}
+
+.animate-shimmer {
+  display: inline-block;
+  color: transparent;
+  background-image: linear-gradient(
+    90deg,
+    var(--muted-foreground) 0%,
+    var(--muted-foreground) 40%,
+    var(--foreground) 50%,
+    var(--muted-foreground) 60%,
+    var(--muted-foreground) 100%
+  );
+  background-size: 300% 100%;
+  -webkit-background-clip: text;
+  background-clip: text;
+  -webkit-text-fill-color: transparent;
+  animation: shimmer 1.5s linear infinite;
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .animate-shimmer {
+    animation: none;
+    color: var(--muted-foreground);
+    -webkit-text-fill-color: var(--muted-foreground);
+  }
+}

examples/harness-chat/app/layout.tsx

@@ -0,0 +1,36 @@
+import type { Metadata } from "next";
+import { Geist, Geist_Mono } from "next/font/google";
+import "streamdown/styles.css";
+import "./globals.css";
+
+const geistSans = Geist({
+  variable: "--font-geist-sans",
+  subsets: ["latin"],
+});
+
+const geistMono = Geist_Mono({
+  variable: "--font-geist-mono",
+  subsets: ["latin"],
+});
+
+export const metadata: Metadata = {
+  title: "json-render Harness Agent Example",
+  description:
+    "A coding agent harness (Claude Code) that reports its work as generative UI via json-render",
+};
+
+export default function RootLayout({
+  children,
+}: {
+  children: React.ReactNode;
+}) {
+  return (
+    <html lang="en" suppressHydrationWarning>
+      <body
+        className={`${geistSans.variable} ${geistMono.variable} font-sans antialiased`}
+      >
+        {children}
+      </body>
+    </html>
+  );
+}

examples/harness-chat/app/page.tsx

@@ -0,0 +1,583 @@
+"use client";
+
+import { useCallback, useRef, useState } from "react";
+import { useChat } from "@ai-sdk/react";
+import { DefaultChatTransport, type UIMessage } from "ai";
+import {
+  SPEC_DATA_PART,
+  SPEC_DATA_PART_TYPE,
+  type SpecDataPart,
+} from "@json-render/core";
+import { useJsonRenderMessage } from "@json-render/react";
+import {
+  ArrowUp,
+  Bug,
+  ChevronRight,
+  FilePen,
+  FilePlus,
+  FileText,
+  FolderGit2,
+  FolderSearch,
+  FolderTree,
+  Gauge,
+  Globe,
+  Hammer,
+  ListChecks,
+  Loader2,
+  Search,
+  SquareChevronRight,
+  Wrench,
+  type LucideIcon,
+} from "lucide-react";
+import { Streamdown } from "streamdown";
+import { code } from "@streamdown/code";
+
+import { ReportRenderer } from "@/lib/render/renderer";
+import {
+  AGENT_IDS,
+  AGENTS,
+  type AgentId,
+  DEFAULT_AGENT_ID,
+} from "@/lib/agents";
+
+type AppDataParts = { [SPEC_DATA_PART]: SpecDataPart };
+type AppMessage = UIMessage<unknown, AppDataParts>;
+
+const transport = new DefaultChatTransport({ api: "/api/agent" });
+
+const SUGGESTIONS: Array<{
+  label: string;
+  description: string;
+  icon: LucideIcon;
+  prompt: string;
+}> = [
+  {
+    label: "Build & test a library",
+    description: "Scaffold a TS package with vitest and run the suite.",
+    icon: Hammer,
+    prompt:
+      "Scaffold a tiny TypeScript semver-parsing library with vitest tests, run the tests, and report the results.",
+  },
+  {
+    label: "Fix failing code",
+    description: "Plant a subtle bug, then debug it end to end.",
+    icon: Bug,
+    prompt:
+      "Create a small JS module with a subtle off-by-one bug and a failing test, then diagnose and fix it like a real debugging session.",
+  },
+  {
+    label: "Benchmark something",
+    description: "Measure two approaches and chart the numbers.",
+    icon: Gauge,
+    prompt:
+      "Write and run a quick benchmark comparing JSON.parse vs a streaming JSON parser on a 5MB file, and report the numbers as a bar chart.",
+  },
+  {
+    label: "Explore a repo",
+    description: "Clone a project and map out what each part does.",
+    icon: FolderGit2,
+    prompt:
+      "Clone github.com/vercel-labs/json-render, explore the package structure, and report what each package does.",
+  },
+];
+
+/** Per-tool icon + readable [running, done] labels (labels used for a11y). */
+const TOOL_META: Record<
+  string,
+  { icon: LucideIcon; labels: [string, string] }
+> = {
+  bash: {
+    icon: SquareChevronRight,
+    labels: ["Running command", "Ran command"],
+  },
+  read: { icon: FileText, labels: ["Reading file", "Read file"] },
+  write: { icon: FilePlus, labels: ["Writing file", "Wrote file"] },
+  edit: { icon: FilePen, labels: ["Editing file", "Edited file"] },
+  grep: { icon: Search, labels: ["Searching code", "Searched code"] },
+  glob: { icon: FolderSearch, labels: ["Listing files", "Listed files"] },
+  ls: { icon: FolderTree, labels: ["Listing directory", "Listed directory"] },
+  webSearch: { icon: Globe, labels: ["Searching the web", "Searched the web"] },
+  WebFetch: { icon: Globe, labels: ["Fetching page", "Fetched page"] },
+  TodoWrite: { icon: ListChecks, labels: ["Updating plan", "Updated plan"] },
+};
+
+/** Pull a one-line human hint out of a tool input (command, path, query). */
+function toolInputHint(input: unknown): string | null {
+  if (input == null || typeof input !== "object") return null;
+  const record = input as Record<string, unknown>;
+  const hint =
+    record.command ?? record.file_path ?? record.pattern ?? record.query;
+  return typeof hint === "string" ? hint : null;
+}
+
+function ToolCallDisplay({
+  toolName,
+  state,
+  input,
+  output,
+}: {
+  toolName: string;
+  state: string;
+  input: unknown;
+  output: unknown;
+}) {
+  const [expanded, setExpanded] = useState(false);
+  const isLoading =
+    state !== "output-available" &&
+    state !== "output-error" &&
+    state !== "output-denied";
+  const meta = TOOL_META[toolName];
+  const Icon = meta?.icon ?? Wrench;
+  const label = meta ? meta.labels[isLoading ? 0 : 1] : toolName;
+  const hint = toolInputHint(input);
+
+  return (
+    <div className="group rounded-lg border bg-card px-3 py-2 text-sm shadow-subtle">
+      <button
+        type="button"
+        title={label}
+        aria-label={label}
+        className="flex w-full max-w-full items-center gap-2 text-left"
+        onClick={() => setExpanded((e) => !e)}
+      >
+        <Icon
+          className={`size-3.5 shrink-0 text-muted-foreground ${
+            isLoading && !hint ? "animate-pulse" : ""
+          }`}
+          strokeWidth={1.75}
+        />
+        {hint && (
+          <code
+            className={`truncate font-mono text-xs text-muted-foreground/70 ${
+              isLoading ? "animate-shimmer" : ""
+            }`}
+          >
+            {hint}
+          </code>
+        )}
+        {!isLoading && output != null && (
+          <ChevronRight
+            className={`ml-auto h-3.5 w-3.5 shrink-0 text-muted-foreground/40 transition-transform group-hover:text-muted-foreground ${expanded ? "rotate-90" : ""}`}
+          />
+        )}
+      </button>
+      {expanded && !isLoading && output != null && (
+        <pre className="mt-2 max-h-64 overflow-auto border-t pt-2 text-xs text-muted-foreground whitespace-pre-wrap break-all">
+          {typeof output === "string"
+            ? output
+            : JSON.stringify(output, null, 2)}
+        </pre>
+      )}
+    </div>
+  );
+}
+
+/**
+ * Monochrome agent marks. Claude (svgl) and OpenAI (svgl) are single-path
+ * brand glyphs forced to `currentColor`; Pi uses its namesake π since it has
+ * no published logo. All inherit the surrounding text color.
+ */
+type MarkProps = { className?: string };
+
+function ClaudeMark({ className }: MarkProps) {
+  return (
+    <svg viewBox="0 0 256 257" className={className} aria-hidden="true">
+      <path
+        fill="currentColor"
+        d="m50.228 170.321 50.357-28.257.843-2.463-.843-1.361h-2.462l-8.426-.518-28.775-.778-24.952-1.037-24.175-1.296-6.092-1.297L0 125.796l.583-3.759 5.12-3.434 7.324.648 16.202 1.101 24.304 1.685 17.629 1.037 26.118 2.722h4.148l.583-1.685-1.426-1.037-1.101-1.037-25.147-17.045-27.22-18.017-14.258-10.37-7.713-5.25-3.888-4.925-1.685-10.758 7-7.713 9.397.649 2.398.648 9.527 7.323 20.35 15.75L94.817 91.9l3.889 3.24 1.555-1.102.195-.777-1.75-2.917-14.453-26.118-15.425-26.572-6.87-11.018-1.814-6.61c-.648-2.723-1.102-4.991-1.102-7.778l7.972-10.823L71.42 0 82.05 1.426l4.472 3.888 6.61 15.101 10.694 23.786 16.591 32.34 4.861 9.592 2.592 8.879.973 2.722h1.685v-1.556l1.36-18.211 2.528-22.36 2.463-28.776.843-8.1 4.018-9.722 7.971-5.25 6.222 2.981 5.12 7.324-.713 4.73-3.046 19.768-5.962 30.98-3.889 20.739h2.268l2.593-2.593 10.499-13.934 17.628-22.036 7.778-8.749 9.073-9.657 5.833-4.601h11.018l8.1 12.055-3.628 12.443-11.342 14.388-9.398 12.184-13.48 18.147-8.426 14.518.778 1.166 2.01-.194 30.46-6.481 16.462-2.982 19.637-3.37 8.88 4.148.971 4.213-3.5 8.62-20.998 5.184-24.628 4.926-36.682 8.685-.454.324.519.648 16.526 1.555 7.065.389h17.304l32.21 2.398 8.426 5.574 5.055 6.805-.843 5.184-12.962 6.611-17.498-4.148-40.83-9.721-14-3.5h-1.944v1.167l11.666 11.406 21.387 19.314 26.767 24.887 1.36 6.157-3.434 4.86-3.63-.518-23.526-17.693-9.073-7.972-20.545-17.304h-1.36v1.814l4.73 6.935 25.017 37.59 1.296 11.536-1.814 3.76-6.481 2.268-7.13-1.297-14.647-20.544-15.1-23.138-12.185-20.739-1.49.843-7.194 77.448-3.37 3.953-7.778 2.981-6.48-4.925-3.436-7.972 3.435-15.749 4.148-20.544 3.37-16.333 3.046-20.285 1.815-6.74-.13-.454-1.49.194-15.295 20.999-23.267 31.433-18.406 19.702-4.407 1.75-7.648-3.954.713-7.064 4.277-6.286 25.47-32.405 15.36-20.092 9.917-11.6-.065-1.686h-.583L44.07 198.125l-12.055 1.555-5.185-4.86.648-7.972 2.463-2.593 20.35-13.999-.064.065Z"
+      />
+    </svg>
+  );
+}
+
+function OpenAIMark({ className }: MarkProps) {
+  return (
+    <svg viewBox="0 0 256 260" className={className} aria-hidden="true">
+      <path
+        fill="currentColor"
+        d="M239.184 106.203a64.716 64.716 0 0 0-5.576-53.103C219.452 28.459 191 15.784 163.213 21.74A65.586 65.586 0 0 0 52.096 45.22a64.716 64.716 0 0 0-43.23 31.36c-14.31 24.602-11.061 55.634 8.033 76.74a64.665 64.665 0 0 0 5.525 53.102c14.174 24.65 42.644 37.324 70.446 31.36a64.72 64.72 0 0 0 48.754 21.744c28.481.025 53.714-18.361 62.414-45.481a64.767 64.767 0 0 0 43.229-31.36c14.137-24.558 10.875-55.423-8.083-76.483Zm-97.56 136.338a48.397 48.397 0 0 1-31.105-11.255l1.535-.87 51.67-29.825a8.595 8.595 0 0 0 4.247-7.367v-72.85l21.845 12.636c.218.111.37.32.409.563v60.367c-.056 26.818-21.783 48.545-48.601 48.601Zm-104.466-44.61a48.345 48.345 0 0 1-5.781-32.589l1.534.921 51.722 29.826a8.339 8.339 0 0 0 8.441 0l63.181-36.425v25.221a.87.87 0 0 1-.358.665l-52.335 30.184c-23.257 13.398-52.97 5.431-66.404-17.803ZM23.549 85.38a48.499 48.499 0 0 1 25.58-21.333v61.39a8.288 8.288 0 0 0 4.195 7.316l62.874 36.272-21.845 12.636a.819.819 0 0 1-.767 0L41.353 151.53c-23.211-13.454-31.171-43.144-17.804-66.405v.256Zm179.466 41.695-63.08-36.63L161.73 77.86a.819.819 0 0 1 .768 0l52.233 30.184a48.6 48.6 0 0 1-7.316 87.635v-61.391a8.544 8.544 0 0 0-4.4-7.213Zm21.742-32.69-1.535-.922-51.619-30.081a8.39 8.39 0 0 0-8.492 0L99.98 99.808V74.587a.716.716 0 0 1 .307-.665l52.233-30.133a48.652 48.652 0 0 1 72.236 50.391v.205ZM88.061 139.097l-21.845-12.585a.87.87 0 0 1-.41-.614V65.685a48.652 48.652 0 0 1 79.757-37.346l-1.535.87-51.67 29.825a8.595 8.595 0 0 0-4.246 7.367l-.051 72.697Zm11.868-25.58 28.138-16.217 28.188 16.218v32.434l-28.086 16.218-28.188-16.218-.052-32.434Z"
+      />
+    </svg>
+  );
+}
+
+function PiMark({ className }: MarkProps) {
+  // pi.dev/logo-auto.svg — blocky "Pi" mark. The viewBox is padded a little
+  // past the mark's bounds so it reads slightly smaller than the other marks.
+  return (
+    <svg
+      viewBox="120 120 560 560"
+      className={className}
+      fill="currentColor"
+      aria-hidden="true"
+    >
+      <path
+        fillRule="evenodd"
+        d="M165.29 165.29H517.36V400H400V517.36H282.65V634.72H165.29ZM282.65 282.65V400H400V282.65Z"
+      />
+      <path d="M517.36 400H634.72V634.72H517.36Z" />
+    </svg>
+  );
+}
+
+const AGENT_MARKS: Record<AgentId, (props: MarkProps) => React.ReactNode> = {
+  "claude-code": ClaudeMark,
+  codex: OpenAIMark,
+  pi: PiMark,
+};
+
+/** Segmented control for picking the coding agent before a chat starts. */
+function AgentSelector({
+  value,
+  onChange,
+}: {
+  value: AgentId;
+  onChange: (id: AgentId) => void;
+}) {
+  return (
+    <div className="inline-flex items-center gap-0.5 rounded-lg border bg-card p-0.5">
+      {AGENT_IDS.map((id) => {
+        const Mark = AGENT_MARKS[id];
+        return (
+          <button
+            key={id}
+            type="button"
+            onClick={() => onChange(id)}
+            aria-pressed={value === id}
+            className={`inline-flex items-center gap-1.5 rounded-md px-2.5 py-1 text-xs font-medium transition-colors ${
+              value === id
+                ? "bg-foreground text-background"
+                : "text-muted-foreground hover:text-foreground"
+            }`}
+          >
+            <Mark className="h-3.5 w-3.5" />
+            {AGENTS[id].label}
+          </button>
+        );
+      })}
+    </div>
+  );
+}
+
+/** Shimmering status line shown while we wait for the agent to produce output. */
+function PendingLine({ label }: { label: string }) {
+  return (
+    <div className="text-sm text-muted-foreground animate-shimmer">{label}</div>
+  );
+}
+
+function MessageBubble({
+  message,
+  isLast,
+  isStreaming,
+  pendingLabel,
+}: {
+  message: AppMessage;
+  isLast: boolean;
+  isStreaming: boolean;
+  pendingLabel: string;
+}) {
+  const { spec, text, hasSpec } = useJsonRenderMessage(message.parts);
+
+  if (message.role === "user") {
+    return (
+      <div className="flex justify-end">
+        <div className="max-w-[85%] rounded-2xl rounded-tr-sm bg-foreground px-3.5 py-2 text-sm leading-relaxed whitespace-pre-wrap text-background">
+          {text}
+        </div>
+      </div>
+    );
+  }
+
+  // Ordered segments: adjacent text merged, adjacent tool calls grouped,
+  // the spec rendered inline where the agent emitted it.
+  const segments: Array<
+    | { kind: "text"; text: string }
+    | {
+        kind: "tools";
+        tools: Array<{
+          toolCallId: string;
+          toolName: string;
+          state: string;
+          input: unknown;
+          output: unknown;
+        }>;
+      }
+    | { kind: "spec" }
+  > = [];
+  let specInserted = false;
+
+  for (const part of message.parts) {
+    if (part.type === "text") {
+      if (!part.text.trim()) continue;
+      const last = segments[segments.length - 1];
+      if (last?.kind === "text") last.text += part.text;
+      else segments.push({ kind: "text", text: part.text });
+    } else if (part.type.startsWith("tool-")) {
+      const tp = part as {
+        type: string;
+        toolCallId: string;
+        state: string;
+        input?: unknown;
+        output?: unknown;
+      };
+      const tool = {
+        toolCallId: tp.toolCallId,
+        toolName: tp.type.replace(/^tool-/, ""),
+        state: tp.state,
+        input: tp.input,
+        output: tp.output,
+      };
+      const last = segments[segments.length - 1];
+      if (last?.kind === "tools") last.tools.push(tool);
+      else segments.push({ kind: "tools", tools: [tool] });
+    } else if (part.type === SPEC_DATA_PART_TYPE && !specInserted) {
+      segments.push({ kind: "spec" });
+      specInserted = true;
+    }
+  }
+
+  const showLoader = isLast && isStreaming && segments.length === 0 && !hasSpec;
+
+  return (
+    <div className="flex w-full flex-col gap-3">
+      {segments.map((seg, i) => {
+        if (seg.kind === "text") {
+          return (
+            <div key={`text-${i}`} className="markdown text-sm leading-relaxed">
+              <Streamdown
+                plugins={{ code }}
+                animated={isLast && isStreaming && i === segments.length - 1}
+              >
+                {seg.text}
+              </Streamdown>
+            </div>
+          );
+        }
+        if (seg.kind === "spec") {
+          if (!hasSpec) return null;
+          return (
+            <div key="spec" className="w-full">
+              <ReportRenderer spec={spec} loading={isLast && isStreaming} />
+            </div>
+          );
+        }
+        return (
+          <div key={`tools-${i}`} className="flex flex-col gap-1.5">
+            {seg.tools.map((t) => (
+              <ToolCallDisplay
+                key={t.toolCallId}
+                toolName={t.toolName}
+                state={t.state}
+                input={t.input}
+                output={t.output}
+              />
+            ))}
+          </div>
+        );
+      })}
+
+      {showLoader && <PendingLine label={pendingLabel} />}
+
+      {hasSpec && !specInserted && (
+        <div className="w-full">
+          <ReportRenderer spec={spec} loading={isLast && isStreaming} />
+        </div>
+      )}
+    </div>
+  );
+}
+
+export default function HarnessChatPage() {
+  const [input, setInput] = useState("");
+  const [agentId, setAgentId] = useState<AgentId>(DEFAULT_AGENT_ID);
+  const [chatId, setChatId] = useState(() => crypto.randomUUID());
+  const [isResetting, setIsResetting] = useState(false);
+  const inputRef = useRef<HTMLTextAreaElement>(null);
+
+  const { messages, sendMessage, setMessages, status, error, id, stop } =
+    useChat<AppMessage>({ transport, id: chatId });
+
+  const isStreaming = status === "streaming" || status === "submitted";
+  const isBusy = isStreaming || isResetting;
+
+  const handleSubmit = useCallback(
+    async (text?: string) => {
+      const message = text || input;
+      if (!message.trim() || isBusy) return;
+      setInput("");
+      // The server locks the agent to the chat on the first message; sending
+      // it every turn is harmless and keeps follow-ups consistent.
+      await sendMessage({ text: message.trim() }, { body: { agent: agentId } });
+    },
+    [input, isBusy, sendMessage, agentId],
+  );
+
+  const handleClear = useCallback(async () => {
+    if (isResetting) return;
+    setIsResetting(true);
+    stop();
+
+    // Drop the server-side harness session (and its sandbox) for this chat.
+    try {
+      await fetch(`/api/agent?id=${encodeURIComponent(id)}`, {
+        method: "DELETE",
+      });
+    } finally {
+      setMessages([]);
+      setChatId(crypto.randomUUID());
+      setInput("");
+      setIsResetting(false);
+      inputRef.current?.focus();
+    }
+  }, [id, isResetting, setMessages, stop]);
+
+  const isEmpty = messages.length === 0;
+
+  return (
+    <div className="flex h-screen flex-col overflow-hidden">
+      {/* The header only appears once a chat has started; the first screen is
+          headerless so the brand title carries it. */}
+      {!isEmpty && (
+        <header className="sticky top-0 z-10 flex h-14 shrink-0 items-center justify-between border-b bg-background/80 px-5 backdrop-blur-md">
+          {/* Left: active agent */}
+          {(() => {
+            const Mark = AGENT_MARKS[agentId];
+            return (
+              <span className="flex items-center gap-1.5 text-sm text-muted-foreground">
+                <Mark className="h-3.5 w-3.5" />
+                {AGENTS[agentId].label}
+              </span>
+            );
+          })()}
+          {/* Center: brand, absolutely centered so side widths can't shift it */}
+          <h1 className="pointer-events-none absolute left-1/2 -translate-x-1/2 text-sm font-medium tracking-tight whitespace-nowrap text-muted-foreground">
+            AI SDK <span className="font-mono">HarnessAgent</span>
+            <span className="mx-1.5 font-normal">+</span>
+            <span className="font-mono">json-render</span>
+          </h1>
+          {/* Right: reset */}
+          <button
+            onClick={handleClear}
+            disabled={isResetting}
+            className="-mr-1.5 rounded-md px-2.5 py-1.5 text-sm text-muted-foreground transition-colors hover:bg-accent hover:text-accent-foreground disabled:cursor-not-allowed disabled:opacity-50"
+          >
+            Start over
+          </button>
+        </header>
+      )}
+
+      <main className="flex flex-1 flex-col overflow-auto">
+        {isEmpty ? (
+          <div className="flex flex-1 flex-col items-center justify-center px-6">
+            <div className="w-full max-w-3xl">
+              <div className="space-y-3">
+                <h2 className="text-3xl font-semibold tracking-tight">
+                  AI SDK <span className="font-mono">HarnessAgent</span>
+                  <span className="mx-1.5 font-normal text-muted-foreground">
+                    +
+                  </span>
+                  <span className="font-mono">json-render</span>
+                </h2>
+                <p className="max-w-md text-[15px] leading-relaxed text-muted-foreground">
+                  A coding agent works in a live sandbox, then reports back as
+                  rendered UI — steps, diffs, terminal output, tests, and charts
+                  — instead of a wall of markdown.
+                </p>
+              </div>
+              <div className="mt-8 grid grid-cols-1 gap-px overflow-hidden rounded-xl border bg-border sm:grid-cols-2">
+                {SUGGESTIONS.map((s) => {
+                  const Icon = s.icon;
+                  return (
+                    <button
+                      key={s.label}
+                      onClick={() => handleSubmit(s.prompt)}
+                      disabled={isBusy}
+                      className="group flex items-start gap-3 bg-card p-4 text-left transition-colors hover:bg-accent"
+                    >
+                      <Icon
+                        className="mt-0.5 h-4 w-4 shrink-0 text-muted-foreground transition-colors group-hover:text-foreground"
+                        strokeWidth={1.75}
+                      />
+                      <span className="min-w-0 space-y-0.5">
+                        <span className="block text-sm font-medium tracking-tight">
+                          {s.label}
+                        </span>
+                        <span className="block text-[13px] leading-snug text-muted-foreground">
+                          {s.description}
+                        </span>
+                      </span>
+                    </button>
+                  );
+                })}
+              </div>
+            </div>
+          </div>
+        ) : (
+          <div className="mx-auto w-full max-w-3xl space-y-6 px-6 py-6">
+            {messages.map((message, index) => (
+              <MessageBubble
+                key={message.id}
+                message={message}
+                isLast={index === messages.length - 1}
+                isStreaming={isStreaming}
+                pendingLabel={index <= 1 ? "Starting sandbox…" : "Working…"}
+              />
+            ))}
+            {isStreaming && messages[messages.length - 1]?.role === "user" && (
+              <PendingLine
+                label={messages.length <= 1 ? "Starting sandbox…" : "Working…"}
+              />
+            )}
+            {error && (
+              <div className="rounded-lg border border-destructive/50 bg-destructive/10 px-4 py-3 text-sm text-destructive">
+                {error.message}
+              </div>
+            )}
+          </div>
+        )}
+      </main>
+
+      <div className="shrink-0 px-6 pb-5">
+        {isEmpty && (
+          <div className="mx-auto mb-2.5 flex max-w-3xl items-center gap-2">
+            <span className="text-xs text-muted-foreground">Agent</span>
+            <AgentSelector value={agentId} onChange={setAgentId} />
+          </div>
+        )}
+        <div className="group relative mx-auto max-w-3xl rounded-xl border bg-card shadow-subtle transition-colors focus-within:border-ring">
+          <textarea
+            ref={inputRef}
+            value={input}
+            onChange={(e) => setInput(e.target.value)}
+            onKeyDown={(e) => {
+              if (e.key === "Enter" && !e.shiftKey) {
+                e.preventDefault();
+                handleSubmit();
+              }
+            }}
+            placeholder={
+              isEmpty
+                ? "Scaffold a TypeScript library and run its tests…"
+                : "Ask a follow-up…"
+            }
+            rows={2}
+            className="w-full resize-none bg-transparent px-3.5 py-3 pr-12 text-sm leading-relaxed placeholder:text-muted-foreground focus-visible:outline-none"
+            autoFocus
+          />
+          <button
+            onClick={() => handleSubmit()}
+            disabled={!input.trim() || isBusy}
+            className="absolute right-2.5 bottom-2.5 flex h-7 w-7 items-center justify-center rounded-lg bg-foreground text-background transition-opacity hover:opacity-90 disabled:cursor-not-allowed disabled:opacity-25"
+          >
+            {isBusy ? (
+              <Loader2 className="h-3.5 w-3.5 animate-spin" />
+            ) : (
+              <ArrowUp className="h-3.5 w-3.5" strokeWidth={2.25} />
+            )}
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}

examples/harness-chat/eslint.config.js

@@ -0,0 +1,11 @@
+import { nextJsConfig } from "@internal/eslint-config/next-js";
+
+/** @type {import("eslint").Linter.Config[]} */
+export default [
+  ...nextJsConfig,
+  {
+    rules: {
+      "react/prop-types": "off",
+    },
+  },
+];

examples/harness-chat/lib/agent.ts

@@ -0,0 +1,161 @@
+import {
+  HarnessAgent,
+  type HarnessAgentAdapter,
+  type HarnessAgentSession,
+} from "@ai-sdk/harness/agent";
+import { createClaudeCode } from "@ai-sdk/harness-claude-code";
+import { createCodex } from "@ai-sdk/harness-codex";
+import { createPi } from "@ai-sdk/harness-pi";
+import { createVercelSandbox } from "@ai-sdk/sandbox-vercel";
+import { agentReportCatalog } from "./render/catalog";
+import { type AgentId } from "./agents";
+
+const AGENT_INSTRUCTIONS = `You are a coding agent running inside a fresh Linux sandbox with Node.js available. The user gives you software tasks; you do the work with your tools (bash, file edits, web search), then report back.
+
+REPORTING:
+Your chat output is rendered in a web UI that understands a JSON component spec. After finishing the work for a turn:
+1. Write one or two short conversational sentences about the outcome.
+2. Then output a UI report as a JSONL spec wrapped in a \`\`\`spec fence.
+
+Make the report reflect what actually happened, drawing from your real session:
+- Steps for the plan you executed (statuses: done/error; use active/pending only if work remains).
+- FileChange entries for files you created, modified, or deleted.
+- Terminal for important commands you ran and their real output (trim long output).
+- TestResults when you ran a test suite.
+- Metric for headline numbers (files changed, tests passed, duration).
+- BarChart to compare numbers across labeled categories (e.g. bundle size per module, benchmark per case).
+- LineChart for a number that changes across an ordered sequence (e.g. coverage per commit, latency over runs).
+- CodeBlock for the key snippet worth showing, with the file path as title.
+- Callout for risks, caveats, or suggested follow-ups.
+- Group sections with Card; never nest Cards.
+
+Never invent results. If something failed, show it (error step, non-zero exit, failed tests) and say what you would try next.
+
+Never use emojis -- not in prose, headings, labels, callouts, or any text field. The UI components supply their own icons.
+
+${agentReportCatalog.prompt({
+  mode: "inline",
+  customRules: [
+    "Keep reports compact and information-dense; the UI renders inside a chat thread.",
+    "Prefer Grid with columns='2' or '3' for Metric rows.",
+    "Use real command output captured during the session in Terminal components.",
+    "Never put emojis in any text field; the components already provide icons.",
+  ],
+})}`;
+
+const gatewayKey = process.env.AI_GATEWAY_API_KEY;
+
+// Each agent runs in its own fresh Node sandbox.
+const sandbox = () => createVercelSandbox({ runtime: "node24", ports: [3000] });
+
+/**
+ * Build the HarnessAgent for an agent id. Both adapters need a `as unknown`
+ * cast on current canaries: they pin zod@3 while the rest of the tree resolves
+ * zod@4, so their HarnessV1 type carries a different provider-utils instance.
+ * Type-level only.
+ */
+function createAgent(id: AgentId): HarnessAgent {
+  if (id === "codex") {
+    const auth = gatewayKey
+      ? { gateway: { apiKey: gatewayKey } }
+      : process.env.OPENAI_API_KEY
+        ? { openai: { apiKey: process.env.OPENAI_API_KEY } }
+        : undefined;
+    return new HarnessAgent({
+      harness: createCodex({
+        auth,
+        model: process.env.CODEX_MODEL,
+      }) as unknown as HarnessAgentAdapter,
+      sandbox: sandbox(),
+      instructions: AGENT_INSTRUCTIONS,
+    });
+  }
+
+  if (id === "pi") {
+    // Pi reads gateway credentials from process.env when auth is omitted; we
+    // pass it explicitly when set for parity with the other agents.
+    return new HarnessAgent({
+      harness: createPi({
+        auth: gatewayKey ? { gateway: { apiKey: gatewayKey } } : undefined,
+        model: process.env.PI_MODEL,
+      }) as unknown as HarnessAgentAdapter,
+      sandbox: sandbox(),
+      instructions: AGENT_INSTRUCTIONS,
+    });
+  }
+
+  const auth = gatewayKey
+    ? { gateway: { apiKey: gatewayKey } }
+    : process.env.ANTHROPIC_API_KEY
+      ? { anthropic: { apiKey: process.env.ANTHROPIC_API_KEY } }
+      : undefined;
+  return new HarnessAgent({
+    harness: createClaudeCode({
+      auth,
+      model: process.env.CLAUDE_CODE_MODEL,
+    }) as unknown as HarnessAgentAdapter,
+    sandbox: sandbox(),
+    instructions: AGENT_INSTRUCTIONS,
+  });
+}
+
+// One HarnessAgent instance per agent id, built lazily and reused.
+const agents = new Map<AgentId, HarnessAgent>();
+function getAgent(id: AgentId): HarnessAgent {
+  let agent = agents.get(id);
+  if (!agent) {
+    agent = createAgent(id);
+    agents.set(id, agent);
+  }
+  return agent;
+}
+
+/**
+ * One live harness session per chat. A session owns the sandbox and the
+ * runtime's own conversation history, so follow-up messages in the same chat
+ * keep working against the same workspace. The session is bound to the agent
+ * that created it, so the chosen agent is locked for the life of the chat.
+ *
+ * In-memory only -- fine for a dev-server example. A production app would
+ * persist `session.detach()` state and resume by sessionId instead.
+ */
+type SessionEntry = {
+  session: HarnessAgentSession;
+  agent: HarnessAgent;
+  agentId: AgentId;
+  expireTimer: NodeJS.Timeout;
+};
+
+const sessions = new Map<string, SessionEntry>();
+
+const SESSION_IDLE_MS = 10 * 60 * 1000;
+
+export async function getSession(
+  chatId: string,
+  agentId: AgentId,
+): Promise<SessionEntry> {
+  const existing = sessions.get(chatId);
+  if (existing) {
+    existing.expireTimer.refresh();
+    return existing;
+  }
+
+  const agent = getAgent(agentId);
+  const session = await agent.createSession();
+  const expireTimer = setTimeout(() => {
+    sessions.delete(chatId);
+    session.destroy().catch(() => {});
+  }, SESSION_IDLE_MS);
+  expireTimer.unref?.();
+  const entry: SessionEntry = { session, agent, agentId, expireTimer };
+  sessions.set(chatId, entry);
+  return entry;
+}
+
+export function dropSession(chatId: string): void {
+  const entry = sessions.get(chatId);
+  if (!entry) return;
+  clearTimeout(entry.expireTimer);
+  sessions.delete(chatId);
+  entry.session.destroy().catch(() => {});
+}

examples/harness-chat/lib/agents.ts

@@ -0,0 +1,21 @@
+/**
+ * Agent catalog — client-safe metadata shared by the UI selector and the
+ * server route. Kept free of server-only imports (harness/sandbox SDKs) so it
+ * can be imported from client components without leaking those into the bundle.
+ * The actual harness construction lives in `lib/agent.ts`.
+ */
+export const AGENTS = {
+  "claude-code": { label: "Claude Code" },
+  codex: { label: "Codex" },
+  pi: { label: "Pi" },
+} as const;
+
+export type AgentId = keyof typeof AGENTS;
+
+export const AGENT_IDS = Object.keys(AGENTS) as AgentId[];
+
+export const DEFAULT_AGENT_ID: AgentId = "claude-code";
+
+export function isAgentId(value: unknown): value is AgentId {
+  return typeof value === "string" && value in AGENTS;
+}

examples/harness-chat/lib/render/catalog.ts

@@ -0,0 +1,226 @@
+import { defineCatalog } from "@json-render/core";
+import { schema } from "@json-render/react/schema";
+import { z } from "zod";
+
+/**
+ * json-render + HarnessAgent Example Catalog
+ *
+ * Components for a coding agent (Claude Code running in a Vercel Sandbox)
+ * to report its work as structured UI: plans, commands, file changes,
+ * test results, and summaries.
+ */
+export const agentReportCatalog = defineCatalog(schema, {
+  components: {
+    Stack: {
+      props: z.object({
+        direction: z.enum(["horizontal", "vertical"]).nullable(),
+        gap: z.enum(["sm", "md", "lg"]).nullable(),
+      }),
+      slots: ["default"],
+      description: "Flex container for laying out children",
+      example: { direction: "vertical", gap: "md" },
+    },
+
+    Grid: {
+      props: z.object({
+        columns: z.enum(["2", "3"]).nullable(),
+      }),
+      slots: ["default"],
+      description: "Multi-column grid layout",
+      example: { columns: "2" },
+    },
+
+    Card: {
+      props: z.object({
+        title: z.string().nullable(),
+        description: z.string().nullable(),
+      }),
+      slots: ["default"],
+      description: "Container card grouping related content, never nested",
+      example: { title: "Test results" },
+    },
+
+    Heading: {
+      props: z.object({
+        text: z.string(),
+        level: z.enum(["1", "2", "3"]).nullable(),
+      }),
+      description: "Section heading",
+      example: { text: "What I changed", level: "2" },
+    },
+
+    Text: {
+      props: z.object({
+        content: z.string(),
+        muted: z.boolean().nullable(),
+      }),
+      description: "Paragraph of text",
+      example: { content: "All tests pass after the fix." },
+    },
+
+    Badge: {
+      props: z.object({
+        label: z.string(),
+        tone: z.enum(["neutral", "success", "warning", "error"]).nullable(),
+      }),
+      description: "Small status label",
+      example: { label: "passing", tone: "success" },
+    },
+
+    Callout: {
+      props: z.object({
+        title: z.string().nullable(),
+        content: z.string(),
+        tone: z.enum(["info", "success", "warning", "error"]).nullable(),
+      }),
+      description: "Highlighted note for key takeaways, risks, or follow-ups",
+      example: {
+        title: "Follow-up",
+        content: "Consider adding a regression test for the edge case.",
+        tone: "info",
+      },
+    },
+
+    Metric: {
+      props: z.object({
+        label: z.string(),
+        value: z.string(),
+        detail: z.string().nullable(),
+      }),
+      description: "Key number with a label (files changed, duration, etc.)",
+      example: { label: "Files changed", value: "4", detail: "+120 / -36" },
+    },
+
+    Steps: {
+      props: z.object({
+        items: z.array(
+          z.object({
+            title: z.string(),
+            detail: z.string().nullable(),
+            status: z.enum(["done", "active", "pending", "error"]),
+          }),
+        ),
+      }),
+      description: "Ordered list of work steps with per-step status",
+      example: {
+        items: [
+          { title: "Reproduce the failure", detail: null, status: "done" },
+          { title: "Fix the off-by-one", detail: null, status: "active" },
+        ],
+      },
+    },
+
+    FileChange: {
+      props: z.object({
+        path: z.string(),
+        kind: z.enum(["created", "modified", "deleted"]),
+        summary: z.string().nullable(),
+        additions: z.number().nullable(),
+        deletions: z.number().nullable(),
+      }),
+      description: "One changed file with what was done to it",
+      example: {
+        path: "src/parser.ts",
+        kind: "modified",
+        summary: "Handle empty input in tokenize()",
+        additions: 12,
+        deletions: 3,
+      },
+    },
+
+    CodeBlock: {
+      props: z.object({
+        code: z.string(),
+        language: z.string().nullable(),
+        title: z.string().nullable(),
+      }),
+      description: "Syntax-highlighted code snippet",
+      example: {
+        code: "export const sum = (a: number, b: number) => a + b;",
+        language: "typescript",
+        title: "src/sum.ts",
+      },
+    },
+
+    Terminal: {
+      props: z.object({
+        command: z.string(),
+        output: z.string().nullable(),
+        exitCode: z.number().nullable(),
+      }),
+      description: "A command that was run and its output",
+      example: {
+        command: "pnpm test",
+        output: "12 passed, 0 failed",
+        exitCode: 0,
+      },
+    },
+
+    TestResults: {
+      props: z.object({
+        passed: z.number(),
+        failed: z.number(),
+        skipped: z.number().nullable(),
+        failures: z
+          .array(
+            z.object({
+              name: z.string(),
+              message: z.string(),
+            }),
+          )
+          .nullable(),
+      }),
+      description: "Test run summary with optional failure details",
+      example: { passed: 11, failed: 1, skipped: 0, failures: null },
+    },
+
+    BarChart: {
+      props: z.object({
+        title: z.string().nullable(),
+        data: z.array(
+          z.object({
+            label: z.string(),
+            value: z.number(),
+          }),
+        ),
+        unit: z.string().nullable(),
+      }),
+      description:
+        "Bar chart comparing labeled numeric values (e.g. bundle size per module, benchmark per case). Pass already-computed numbers; do not aggregate raw data.",
+      example: {
+        title: "Build time by package",
+        data: [
+          { label: "core", value: 1.2 },
+          { label: "react", value: 2.8 },
+          { label: "cli", value: 0.6 },
+        ],
+        unit: "s",
+      },
+    },
+
+    LineChart: {
+      props: z.object({
+        title: z.string().nullable(),
+        data: z.array(
+          z.object({
+            label: z.string(),
+            value: z.number(),
+          }),
+        ),
+        unit: z.string().nullable(),
+      }),
+      description:
+        "Line chart showing a numeric value as it changes across an ordered sequence (e.g. coverage per commit, latency over runs). Points are connected in array order.",
+      example: {
+        title: "Coverage over commits",
+        data: [
+          { label: "a1b2", value: 71 },
+          { label: "c3d4", value: 78 },
+          { label: "e5f6", value: 84 },
+        ],
+        unit: "%",
+      },
+    },
+  },
+  actions: {},
+});