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OpenAPI to MCP Generator

by harsha-iiiv

API/Management & ToolsOpenAPIAPIGeneratorProxyZodTypeScript

This CLI tool automates the generation of MCP-compatible servers that proxy requests to existing REST APIs. It enables AI agents and other MCP clients to seamlessly interact with your APIs using either standard input/output or HTTP-based transport.

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OpenAPI to MCP Generator (openapi-mcp-generator)

npm version

npm version

License: MIT

License: MIT
GitHub repository

GitHub repository

Generate Model Context Protocol (MCP) servers from OpenAPI specifications.

This CLI tool automates the generation of MCP-compatible servers that proxy requests to existing REST APIs—enabling AI agents and other MCP clients to seamlessly interact with your APIs using either standard input/output or HTTP-based transport.

✨ Features

  • 🔧 OpenAPI 3.0 Support: Converts any OpenAPI 3.0+ spec into an MCP-compatible server.
  • 🔁 Proxy Behavior: Proxies calls to your original REST API while validating request structure and security.
  • 🔐 Authentication Support: API keys, Bearer tokens, Basic auth, and OAuth2 supported via environment variables.
  • 🧪 Zod Validation: Automatically generates Zod schemas from OpenAPI definitions for runtime input validation.
  • ⚙️ Typed Server: Fully typed, maintainable TypeScript code output.
  • 💬 Stdio & Web Transport: Communicate over stdio or HTTP (beta, SSE support).
  • 🧰 Project Scaffold: Generates a complete Node.js project with tsconfig.json, package.json, and entry point.
  • 🧪 Built-in HTML Test Client (Web mode): Test API interactions visually in your browser.

🚀 Installation

npm install -g openapi-mcp-generator

You can also use yarn global add openapi-mcp-generator or pnpm add -g openapi-mcp-generator

🛠 Usage

# Generate an MCP server (stdio)
openapi-mcp-generator --input path/to/openapi.json --output path/to/output/dir

# Generate an MCP web server (beta)
openapi-mcp-generator --input path/to/openapi.json --output path/to/output/dir --transport=web --port=3000

CLI Options

| Option | Alias | Description | Default | |--------------------|-------|-----------------------------------------------------------------------------------------------------|---------------------------------| | --input | -i | Path or URL to OpenAPI specification (YAML or JSON) | Required | | --output | -o | Directory to output the generated MCP project | Required | | --server-name | -n | Name of the MCP server (package.json:name) | OpenAPI title or mcp-api-server | | --server-version | -v | Version of the MCP server (package.json:version) | OpenAPI version or 1.0.0 | | --base-url | -b | Base URL for API requests. Required if OpenAPI servers missing or ambiguous. | Auto-detected if possible | | --transport | -t | Transport mode: "stdio" (default) or "web" (beta) | "stdio" | | --port | -p | Port for web server mode | 3000 | | --force | | Overwrite existing files in the output directory without confirmation | false |

🧱 Project Structure

The generated project includes:

<output_directory>/
├── .gitignore
├── package.json
├── tsconfig.json
└── src/
    └── index.ts
  • Uses axios, zod, @modelcontextprotocol/sdk, and json-schema-to-zod
  • Secure API key/tokens via environment variables
  • Tool generation for each endpoint

📡 Transport Modes

Stdio (Default)

Communicates with MCP clients via standard input/output. Ideal for local development or integration with LLM tools.

Web Server Mode (Beta)

Launches a fully functional HTTP server with:

  • Server-Sent Events (SSE) for bidirectional messaging
  • REST endpoint for client → server communication
  • In-browser test client UI
  • Multi-connection support

⚠️ Note: Web mode is experimental and may have breaking changes in future updates.

🔐 Environment Variables for Authentication

Configure auth credentials in your environment:

| Auth Type | Variable Format | |-------------|----------------------------------------------------------| | API Key | API_KEY_<SCHEME_NAME> | | Bearer | BEARER_TOKEN_<SCHEME_NAME> | | Basic Auth | BASIC_USERNAME_<SCHEME_NAME>, BASIC_PASSWORD_<SCHEME_NAME> | | OAuth2 | OAUTH_CLIENT_ID_<SCHEME_NAME>, OAUTH_CLIENT_SECRET_<SCHEME_NAME>, OAUTH_SCOPES_<SCHEME_NAME> |

▶️ Running the Generated Server

cd path/to/output/dir
npm install

# Run in stdio mode
npm start

# Run in web server mode (if generated with --transport=web)
npm run start:web

⚠️ Requirements

  • Node.js v18 or later

🤝 Contributing

Contributions are welcome!

  1. Fork the repo
  2. Create a feature branch: git checkout -b feature/amazing-feature
  3. Commit your changes: git commit -m "Add amazing feature"
  4. Push and open a PR

📌 Repository: github.com/harsha-iiiv/openapi-mcp-generator

📄 License

MIT License — see LICENSE for full details.