> ## Documentation Index > Fetch the complete documentation index at: https://toolgrain.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # React and Apps API reference > Public bindings, provider options, and protocol exports. ## createApp `createApp()` from `@toolgrain/react` returns `AppProvider`, `useToolResult`, `useToolCall`, `useHostContext`, and `useHostActions`. It does not read browser globals or connect until mounting. > [!NOTE] > > This reference describes the stable Toolgrain 0.3.0 API. Start with the [Vite walkthrough](https://toolgrain.mintlify.site/mcp-apps/quickstart.md) for a runnable project, then add only the hooks your widget uses. ## AppProvider | Prop | Contract | | - | - | | `appInfo` | Required nonempty name/version; fixed for the mount | | `tool` | A registered tool name for a separate entry; exclusive with `resolveTool` | | `resolveTool` | Shared-entry selector receiving result and host context; returns a registered name or undefined | | `timeoutMs` | Positive integer deadline, default 30000 milliseconds | | `hostOrigin` | Optional exact parent origin; default allows opaque sandbox origins | | `applyHostStyles` | Apply/restore host fonts and CSS variables, default true | | `autoResize` | Report size through ResizeObserver when available, default true | | `availableDisplayModes` | Nonempty readonly list of modes this widget supports; default `["inline"]`, fixed for the mount | | `children` | React component tree sharing this connection | A connection is terminal after closure. Remount to reconnect or change identity/routing. Unmount and teardown remove owned resources. Server rendering does not connect. ## Hooks `useToolResult(name?)` returns status, selected tool name, optional original wire input, full result, and lifecycle/routing error. Without a name, the selected name discriminates the registered tool union. With a name, other active tools appear as waiting. `useToolCall(name)` returns `call(input, options?)`, pending, optional full result, and optional error. Options accept AbortSignal and timeoutMs. Explicit tool errors resolve; RPC/transport failures reject. Each hook tracks its latest invocation independently of the initiating result. `useHostContext()` returns live `AppHostContext`. Fields are optional and self-reported by the host. `useHostActions()` returns `available` and stable request functions: | Function | Parameters | Resolved result | | - | - | - | | `openLink` | Absolute URL string, optional request options | `AppActionResult` | | `sendMessage` | `AppMessageParams`, optional request options | `AppActionResult` | | `updateModelContext` | `AppModelContextParams`, optional request options | `AppActionResult` | | `requestDisplayMode` | `AppDisplayMode`, optional request options | `AppDisplayModeResult` | Request options accept `signal` and `timeoutMs`; the provider default is 30000 milliseconds. Capability/content checks happen before sending. Explicit `isError` acknowledgements resolve; RPC/transport/validation failures reject. The hook owns no pending/error state. See [host actions](https://toolgrain.mintlify.site/mcp-apps/host-actions.md) for availability, replacement context, and actual display-mode behavior. Exported authoring types: `AppProviderProps`, `AppState`, `ToolState`, `ToolName`, `ToolInput`, `ToolResult`, `ToolCall`, and `ToolCallOptions`. Host-action types are `HostActions`, `HostActionAvailability`, and `HostActionOptions`. ## Server and wire contracts `getAppSupport(ctx)` and `AppSupport` are exported by `@toolgrain/mcp`. Existing `mcpResult()` types preserve inferred metadata through an optional second generic parameter; existing single-generic usage remains valid. `@toolgrain/protocol/apps` exports `APPS_PROTOCOL_VERSION`, `APPS_EXTENSION_ID`, `APPS_MIME_TYPE`, `AppToolMeta`, `AppResourceMeta`, `AppHostContext`, `AppHostCapabilities`, `AppDisplayMode`, `AppToolResult`, `AppInitializeParams`, and `AppInitializeResult`. This export has no runtime dependencies and does not replace either supported outer MCP revision. Additional named exports describe resource settings, host presentation, and host-action envelopes: | Type | Contract | | - | - | | `AppResourceCsp` | Readonly domain lists for network, resource, nested-frame, and base-URI CSP directives | | `AppResourcePermissions` | Camera, microphone, geolocation, and clipboard-write requests expressed as empty objects | | `AppTheme` | `light` or `dark` | | `AppStyleVariableKey` | Standardized color, typography, radius, border-width, and shadow token names | | `AppStyleVariables` | Optional standard variables plus string-valued host/application extensions | | `AppHostCss` | Host font-loading CSS and extension fields | | `AppHostStyles` | Variables and CSS supplied in host context | | `AppContentModalities` | Content kinds advertised for optional host actions | | `AppMessageParams` | User role and readonly MCP content-block array | | `AppModelContextParams` | Optional content blocks and object-root structured replacement context | | `AppActionResult` | Host acknowledgement with optional `isError` and preserved extensions | | `AppDisplayModeResult` | Actual selected display mode and preserved extensions | `AppHostCapabilities` now names sandbox grants/CSP, experimental extensions, content-message/context modalities, download support, and sampling tools, alongside existing server tool/resource, link, and logging advertisements. Unknown capability fields are preserved. The [support table](https://toolgrain.mintlify.site/mcp-apps/capabilities.md#react-protocol-support) distinguishes implemented requests from other advertisements. Styling variables are optional. Use CSS fallbacks such as `var(--color-text-primary, #111)` and `var(--font-sans, sans-serif)`. The provider applies supplied variables and font CSS by default; `applyHostStyles={false}` disables that behavior. The metadata guide includes [resource fields and border examples](https://toolgrain.mintlify.site/mcp-apps/security.md#resource-metadata). `AppToolMeta` rejects resource-only CSP/permissions, including when metadata is assigned through another variable. The runtime still preserves supplied metadata; the host owns enforcement. `apps-provenance.json` pins the reviewed [stable specification](https://github.com/modelcontextprotocol/ext-apps/blob/298e884ec3f02daba085acdb02042d73bd00b355/specification/2026-01-26/apps.mdx) and [upstream type reference](https://github.com/modelcontextprotocol/ext-apps/blob/040942b3af064bf76b705021e3472b6593ae839e/src/spec.types.ts), including their SHA-256 hashes. Some type-reference advertisements go beyond the stable prose; their presence alone does not implement a React action. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.