OpenAPI MCP Server

What is OpenAPI MCP Server?

A Model Context Protocol (MCP) server that exposes OpenAPI endpoints as MCP tools, with optional support for MCP prompts and resources. It enables Large Language Models to discover and interact with REST APIs defined by OpenAPI specifications.

How to use OpenAPI MCP Server?

Use the CLI directly with npx @ivotoby/openapi-mcp-server or import the OpenAPIServer class as a library in your Node.js application. Configure via environment variables (e.g., API_BASE_URL, OPENAPI_SPEC_PATH) or command‑line flags (e.g., --api-base-url, --openapi-spec). Supports both stdio (default) and HTTP transport.

Key features of OpenAPI MCP Server

• Exposes OpenAPI endpoints as MCP tools automatically
• Supports loading OpenAPI specs via URL, file, stdin, or inline
• Two transports: stdio (default) and Streamable HTTP
• Mutual TLS (mTLS) support for upstream API authentication
• Tool loading modes: all, dynamic, or explicit
• Filtering by tags and custom headers

Use cases of OpenAPI MCP Server

• Connect Claude Desktop to any REST API via OpenAPI spec
• Allow LLMs to dynamically discover and invoke API actions
• Provide structured tools for API‑driven autonomous agents
• Load private APIs using mTLS or custom CA certificates
• Use with Cursor or any MCP‑compatible client

FAQ from OpenAPI MCP Server

What transport methods does OpenAPI MCP Server support?

Stdio (default) for direct integration with AI systems like Claude Desktop, and Streamable HTTP for web clients and HTTP‑capable systems.

How can I load an OpenAPI specification?

Four methods: provide a URL or local file path with --openapi-spec, pipe the spec via standard input with --spec-from-stdin, pass the spec inline with --spec-inline, or use the corresponding environment variables. Only one source is allowed at a time.

How do I authenticate to the upstream API?

You can set static headers via --headers / API_HEADERS, or use mutual TLS with --client-cert and --client-key options. mTLS is orthogonal to header‑based authentication.

What is the default transport and how do I change it?

The default transport is stdio. Switch to HTTP by setting --transport http (or the TRANSPORT_TYPE environment variable). The HTTP server listens on 127.0.0.1:3000 by default.

Can I use OpenAPI MCP Server as a library?

Yes. Import the OpenAPIServer class in your own Node.js applications for custom implementations, instead of using the CLI tool.