OpenAI Apps MCP

Status: Production Ready ✅ Last Updated: 2026-01-03 Production Tested: Based on Toolbase-AI template, tested with MCP Inspector and ChatGPT

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Auto-Trigger Keywords

Claude Code automatically discovers this skill when you mention:

Primary Keywords

• openai apps
• openai apps sdk
• chatgpt app
• chatgpt app development
• mcp server
• model context protocol
• mcp server openai
• mcp widgets

Secondary Keywords

• cloudflare workers mcp
• hono mcp
• stateless mcp
• window.openai
• ui://widget
• text/html+skybridge
• openai metadata
• tool invocation
• outputTemplate
• mcp inspector

Error-Based Keywords

• "CORS policy blocks MCP"
• "widget returns 404"
• "widget displays as plain text"
• "ASSETS binding undefined"
• "SSE connection drops"
• "ChatGPT doesn't suggest tool"
• "getInitialData returns undefined"
• "widget scripts blocked by CSP"

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What This Skill Does

Build ChatGPT apps (OpenAI Apps) using stateless MCP servers deployed on Cloudflare Workers. Covers the complete setup from MCP protocol implementation to widget serving, with production-tested patterns for OpenAI-specific metadata formats.

Core Capabilities

✅ MCP server setup with @modelcontextprotocol/sdk + Hono ✅ OpenAI-specific metadata formats (outputTemplate, toolInvocation) ✅ Widget serving via Cloudflare Workers Static Assets ✅ CORS configuration for ChatGPT integration ✅ SSE transport patterns with Workers ✅ Tool discovery optimization (action-oriented descriptions) ✅ Widget-to-server communication patterns (window.openai API) ✅ Prevents 8 documented errors (CORS, URIs, MIME types, etc.)

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Known Issues This Skill Prevents

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When to Use This Skill

✅ Use When:

• Building apps for ChatGPT Apps marketplace
• Creating MCP servers specifically for OpenAI integration
• Serving interactive widgets in ChatGPT conversations
• Extending ChatGPT with custom tools and UI
• Deploying to Cloudflare Workers
• You DON'T need persistent state between conversations

❌ Don't Use When:

• Building general MCP servers (use typescript-mcp or fastmcp instead)
• Need stateful agents with conversation history
• Targeting Claude or other AI assistants (not ChatGPT)
• Building Cloudflare AI inference services (that's Workers AI)

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Quick Usage Example

# 1. Scaffold project
npm create cloudflare@latest my-openai-app -- --type hello-world --ts --git --deploy false
cd my-openai-app

# 2. Install dependencies
npm install @modelcontextprotocol/sdk@1.25.1 hono@4.11.3 zod@4.1.13
npm install -D @cloudflare/vite-plugin@1.17.1 vite@7.2.4

# 3. Create MCP server (see SKILL.md for code)
# Create src/index.ts with Hono + MCP server
# Create src/widgets/hello.html

# 4. Deploy
npm run build
npx wrangler deploy

# 5. Test
npx @modelcontextprotocol/inspector https://my-openai-app.workers.dev/mcp

Result: Working MCP server with widget serving, ready to integrate with ChatGPT

Full instructions: See SKILL.md

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Token Efficiency Metrics

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Package Versions (Verified 2026-01-03)

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Dependencies

Prerequisites: None

Integrates With:

• cloudflare-worker-base (optional, helpful for Workers setup patterns)
• hono-routing (optional, helpful for routing patterns)
• typescript-mcp (optional, for general MCP concepts)

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File Structure

openai-apps-mcp/
├── SKILL.md              # Complete documentation
├── README.md             # This file
├── templates/
│   ├── basic/            # Minimal stateless MCP server
│   └── with-react/       # React-based widgets
├── scripts/
│   └── scaffold-openai-app.sh  # Project generator
├── references/
│   ├── mcp-protocol-basics.md
│   ├── openai-metadata-format.md
│   ├── widget-patterns.md
│   └── optional-agents-upgrade.md
└── examples/
    └── hello-world/      # Complete working example

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Official Documentation

• Model Context Protocol: https://modelcontextprotocol.io/
• MCP SDK: https://github.com/modelcontextprotocol/typescript-sdk
• OpenAI Apps SDK: https://developers.openai.com/apps-sdk
• Cloudflare Workers: https://developers.cloudflare.com/workers/
• Hono: https://hono.dev/
• Context7 Library: /modelcontextprotocol/typescript-sdk

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Related Skills

• typescript-mcp - General MCP server development (platform-agnostic)
• fastmcp - Python MCP server development
• cloudflare-worker-base - Cloudflare Workers base setup with Hono + Vite
• hono-routing - Hono routing patterns and validation

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Contributing

Found an issue or have a suggestion?

• Open an issue: https://github.com/jezweb/claude-skills/issues
• See SKILL.md for detailed documentation

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License

MIT License - See main repo LICENSE file

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Production Tested: ✅ Based on Toolbase-AI template, patterns tested with MCP Inspector and ChatGPT developer mode Token Savings: ~70% Error Prevention: 100% (prevents all 8 documented errors) Ready to use! See SKILL.md for complete setup.