OpenAPI to MCP Generator (openapi-mcp-generator)

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 your choice of transport methods.

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✨ 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.
• 🔌 Multiple Transports: Communicate over stdio, SSE via Hono, or StreamableHTTP.
• 🧰 Project Scaffold: Generates a complete Node.js project with tsconfig.json, package.json, and entry point.
• 🧪 Built-in HTML Test Clients: Test API interactions visually in your browser (for web-based transports).

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🚀 Installation

npm install -g openapi-mcp-generator

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

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🛠 Usage

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

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

# Generate an MCP StreamableHTTP server
openapi-mcp-generator --input path/to/openapi.json --output path/to/output/dir --transport=streamable-http --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), "web", or "streamable-http"	"stdio"
--port	-p	Port for web-based transports	3000
--force		Overwrite existing files in the output directory without confirmation	false

📦 Programmatic API

You can also use this package programmatically in your Node.js applications:

import { getToolsFromOpenApi } from 'openapi-mcp-generator';

// Extract MCP tool definitions from an OpenAPI spec
const tools = await getToolsFromOpenApi('./petstore.json');

// With options
const filteredTools = await getToolsFromOpenApi('https://example.com/api-spec.json', {
  baseUrl: 'https://api.example.com',
  dereference: true,
  excludeOperationIds: ['deletePet'],
  filterFn: (tool) => tool.method.toLowerCase() === 'get',
});

For full documentation of the programmatic API, see PROGRAMMATIC_API.md.

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🧱 Project Structure

The generated project includes:

<output_directory>/
├── .gitignore
├── package.json
├── tsconfig.json
├── .env.example
├── src/
│   ├── index.ts
│   └── [transport-specific-files]
└── public/          # For web-based transports
    └── index.html   # Test client

Core dependencies:

• @modelcontextprotocol/sdk - MCP protocol implementation
• axios - HTTP client for API requests
• zod - Runtime validation
• json-schema-to-zod - Convert JSON Schema to Zod
• Transport-specific deps (Hono, uuid, etc.)

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📡 Transport Modes

Stdio (Default)

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

Web Server with SSE

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
• Built with lightweight Hono framework

StreamableHTTP

Implements the MCP StreamableHTTP transport which offers:

• Stateful JSON-RPC over HTTP POST requests
• Session management using HTTP headers
• Proper HTTP response status codes
• Built-in error handling
• Compatibility with MCP StreamableHTTPClientTransport
• In-browser test client UI
• Built with lightweight Hono framework

Transport Comparison

Feature	stdio	web (SSE)	streamable-http
Protocol	JSON-RPC over stdio	JSON-RPC over SSE	JSON-RPC over HTTP
Connection	Persistent	Persistent	Request/response
Bidirectional	Yes	Yes	Yes (stateful)
Multiple clients	No	Yes	Yes
Browser compatible	No	Yes	Yes
Firewall friendly	No	Yes	Yes
Load balancing	No	Limited	Yes
Status codes	No	Limited	Full HTTP codes
Headers	No	Limited	Full HTTP headers
Test client	No	Yes	Yes

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🔐 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>

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▶️ Running the Generated Server

cd path/to/output/dir
npm install

# Run in stdio mode
npm start

# Run in web server mode
npm run start:web

# Run in StreamableHTTP mode
npm run start:http

Testing Web-Based Servers

For web and StreamableHTTP transports, a browser-based test client is automatically generated:

1. Start the server using the appropriate command
2. Open your browser to http://localhost:<port>
3. Use the test client to interact with your MCP server

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⚠️ Requirements

• Node.js v20 or later

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Star History

🤝 Contributing

Contributions are welcome!

1. Fork the repo
2. Create a feature branch: git checkout -b feature/amazing-feature
3. Run npm run format.write to format your code
4. Commit your changes: git commit -m "Add amazing feature"
5. Push and open a PR

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

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📄 License

MIT License — see LICENSE for full details.