fb5e96a719
References existing type-checked examples instead of a stub: - Vanilla JS: `applyHostStyleVariables_fromHostContext` from `src/styles.examples.ts` - React: `useHostStyles_basicUsage` from `src/react/useHostStyles.examples.tsx` Expanded `applyHostStyleVariables_fromHostContext` to show the full pattern: using CSS variables in styles, applying on `onhostcontextchanged`, and applying initial styles after `connect()`. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
77 lines
3 KiB
Markdown
77 lines
3 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.ts#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.ts#errorsToModel}
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## Support native host styling using CSS variables
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Hosts provide CSS variables (e.g., `--color-background-primary`) that match their theme. Apply these to the document, then use them in your styles via `var()`.
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**Vanilla JS:**
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{@includeCode ../src/styles.examples.ts#applyHostStyleVariables_fromHostContext}
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**React:**
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{@includeCode ../src/react/useHostStyles.examples.tsx#useHostStyles_basicUsage}
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## [TODO] Reacting to light/dark theme changes
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{@includeCode ./patterns.ts#lightDarkTheme}
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## [TODO] Support fullscreen / exit fullscreen
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{@includeCode ./patterns.ts#fullscreen}
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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.ts#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.ts#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.ts#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.ts#migrateFromOpenai}
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