OpenAI Apps MCP

Status : Production Ready Last Updated : 2026-01-21 Dependencies : cloudflare-worker-base , hono-routing (optional) Latest Versions : @modelcontextprotocol/sdk@1.25.3, hono@4.11.3, zod@4.3.5, wrangler@4.58.0 Build ChatGPT Apps using MCP (Model Context Protocol) servers on Cloudflare Workers. Extends ChatGPT with custom tools and interactive widgets (HTML/JS UI rendered in iframe). Architecture : ChatGPT → MCP endpoint (JSON-RPC 2.0) → Tool handlers → Widget resources (HTML) Status : Apps available to Business/Enterprise/Edu (GA Nov 13, 2025). MCP Apps Extension (SEP-1865) formalized Nov 21, 2025. CORS : Must allow on /mcp/* routes Widget URI : Must use ui://widget/ prefix (e.g., ui://widget/map.html ) MIME Type : Must be text/html+skybridge for HTML resources Widget Data : Pass via _meta.initialData (accessed via window.openai.getInitialData() ) Tool Descriptions : Action-oriented ("Use this when user wants to...") ASSETS Binding : Serve widgets from ASSETS, not bundled in worker code SSE : Send heartbeat every 30s (100s timeout on Workers) This skill prevents 14 documented issues: Error : Access to fetch blocked by CORS policy Fix : app.use('/mcp/*', cors({ origin: ' })) Error : 404 (Not Found) for widget URL Fix : Use ui://widget/ prefix (not resource:// or /widgets/ ) Error : HTML source code visible instead of rendered widget Fix : MIME type must be text/html+skybridge...