OpenAPI to MCP Generator Project

Harshavardhan Surisetty

Completed work

AI Agent Engineer

Backend Engineer

Axios

Node.js

TypeScript

Computer Software

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.

✨ 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).

🚀 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 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.

🧱 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.)

📡 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

🔐 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
npm run start:web

# Run in StreamableHTTP mode
npm run start:http