dce143e92e
Add `App_onhostcontextchanged_respondToDisplayMode` example showing how to listen for display mode changes and update UI with `classList.toggle()`. Update `App_requestDisplayMode_fullscreen` to `App_requestDisplayMode_toggle` to show the common toggle pattern checking `availableDisplayModes` first. Refactor full examples (pdf-server, shadertoy-server) to use `classList.toggle(class, condition)` instead of add/remove branches. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
83 lines
3.4 KiB
Markdown
83 lines
3.4 KiB
Markdown
---
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title: Patterns
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---
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# MCP Apps Patterns
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This document covers common patterns and recipes for building MCP Apps.
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## Tools that are private to Apps
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Set {@link types!McpUiToolMeta.visibility Tool.\_meta.ui.visibility} to `["app"]` to make tools only callable by Apps (hidden from the model). This is useful for UI-driven actions like updating quantities, toggling settings, or other interactions that shouldn't appear in the model's tool list.
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{@includeCode ../src/server/index.examples.ts#registerAppTool_appOnlyVisibility}
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## [TODO] Authenticated calls from App
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- Use tool calls / read resources
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- See [PDF example](https://github.com/modelcontextprotocol/ext-apps/blob/main/examples/pdf-viewer) to read binaries by chunks to avoid call tool size limitations on platforms like claude.ai
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- Pass auth token in `_meta` (will be loaded again in the future) + refresh token + store in local storage (see Persist data section below)
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{@includeCode ./patterns.tsx#authenticatedCalls}
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## [TODO] Giving errors back to model
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- Before app runs: validate inputs in tool call
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- After it runs: use `updateModelContext`
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{@includeCode ./patterns.tsx#errorsToModel}
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## Matching host styling (CSS variables, theme, and fonts)
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Use the SDK's style helpers to apply host styling, then reference them in your CSS:
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- **CSS variables** — Use `var(--color-background-primary)`, etc. in your CSS
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- **Theme** — Use `[data-theme="dark"]` selectors or `light-dark()` function for theme-aware styles
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- **Fonts** — Use `var(--font-sans)` or `var(--font-mono)` with fallbacks (e.g., `font-family: var(--font-sans, system-ui, sans-serif)`)
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**Vanilla JS:**
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{@includeCode ./patterns.tsx#hostStylingVanillaJs}
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**React:**
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{@includeCode ./patterns.tsx#hostStylingReact}
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## Entering / Exiting fullscreen
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Toggle fullscreen mode by calling {@link app!App.requestDisplayMode requestDisplayMode}:
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{@includeCode ../src/app.examples.ts#App_requestDisplayMode_toggle}
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Listen for display mode changes via {@link app!App.onhostcontextchanged onhostcontextchanged} to update your UI:
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{@includeCode ../src/app.examples.ts#App_onhostcontextchanged_respondToDisplayMode}
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## [TODO] Persist data (incl. widget state)
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- Note: OAI's `window.openai.setWidgetState({modelContent, privateContent, imageIds})` has only a partial equivalent in the MCP Apps spec (for now!): `App.updateModelContext({content, structuredContent})`
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- For data persistence / to reload when conversation is reloaded, you must use localStorage / IndexedDb with `hostInfo.toolInfo.id` as key returned `CallToolResult._meta.widgetUUID = randomUUID()`
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{@includeCode ./patterns.tsx#persistData}
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## [TODO] Lower perceived latency / manage loading time
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Leverage partial inputs to show widgets as possible.
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Beware of partial JSON being partial (but healed), so some of your objects may not be complete (e.g. in a list you may need to skip the last item if your code validates input schemas strictly).
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{@includeCode ./patterns.tsx#lowerPerceivedLatency}
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## [TODO] Supporting both iframe & MCP Apps in same binary
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See recipe: https://github.com/modelcontextprotocol/ext-apps/issues/34
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{@includeCode ./patterns.tsx#iframeAndMcpApps}
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## [TODO] Migrating from OpenAI to MCP Apps
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See [OpenAI -> MCP Apps](https://docs.google.com/document/d/13ROImOR9B8xc32yhqsFyC9Hh3_H63JFORDIyjyIPcU4/edit) migration guide.
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Also: [Managing State](https://platform.openai.com/docs/actions/managing-state) (OpenAI)
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{@includeCode ./patterns.tsx#migrateFromOpenai}
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