OpenAI Apps MCP

SKILL.md

Build ChatGPT apps with MCP servers on Cloudflare Workers, extending ChatGPT with custom tools and interactive HTML/JS widgets.

Implements JSON-RPC 2.0 MCP protocol with tool registration, execution, and widget resource serving via ASSETS binding

Requires CORS allowlist for https://chatgpt.com, ui://widget/ URI prefix for widgets, and text/html+skybridge MIME type

Prevents 14 documented issues including CORS blocks, widget 404s, MIME type misconfigurations, SSE timeouts, and Next.js integration conflicts (fixed in SDK v1.25.3+)

Supports widget state via _meta.initialData, tool-initiated calls with widgetCallable: true flag, and performance optimization under 200ms response targets

Building OpenAI Apps with Stateless MCP Servers

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

Overview

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.