mcp-openapi MCP Server

mcp-openapi

Turn any OpenAPI/Swagger spec into MCP tools — so Claude and other AI assistants can call your REST APIs.

Point mcp-openapi at any OpenAPI 3.x or Swagger 2.0 spec URL and it generates Model Context Protocol (MCP) tools automatically. No code generation, no config files, no boilerplate. Your AI assistant gets callable tools for every API endpoint in seconds.

Quick Start

1. Run it (no install required):

npx mcp-openapi --spec https://petstore3.swagger.io/api/v3/openapi.json

2. Add it to Claude Desktop (claude_desktop_config.json):

{
  "mcpServers": {
    "petstore": {
      "command": "npx",
      "args": [
        "mcp-openapi",
        "--spec", "https://petstore3.swagger.io/api/v3/openapi.json"
      ]
    }
  }
}

3. Ask Claude to use it:

"List all available pets in the store"

Claude sees MCP tools like find_pets_by_status, get_pet_by_id, add_pet and calls them directly.

Why mcp-openapi?

Most MCP-to-API bridges require you to write tool definitions by hand or generate code from a spec. mcp-openapi skips all of that.

Flat parameter schemas are the key differentiator. Instead of passing nested JSON objects (which LLMs frequently get wrong), mcp-openapi flattens path, query, header, and body parameters into a single flat object. This dramatically improves tool-calling accuracy.

How It Works

OpenAPI/Swagger Spec          mcp-openapi               AI Assistant
     (URL or file)                                      (Claude, etc.)
          |                         |                         |
          |   1. Parse & validate   |                         |
          |------------------------>|                         |
          |                         |                         |
          |   2. Generate MCP tools |                         |
          |   (one per endpoint)    |                         |
          |------------------------>|                         |
          |                         |                         |
          |                         |   3. Register tools     |
          |                         |   via stdio transport   |
          |                         |------------------------>|
          |                         |                         |
          |                         |   4. AI calls a tool    |
          |                         |<------------------------|
          |                         |                         |
          |   5. Build & execute    |                         |
          |   HTTP request          |                         |
          |<------------------------|                         |
          |                         |                         |
          |   6. Return truncated   |                         |
          |   response to AI        |                         |
          |------------------------>|------------------------>|

Each API endpoint becomes one MCP tool:

• Tool name is derived from operationId (converted to snake_case) or from method + path
• Parameters are flattened into a single input schema (path, query, header, and body params merged)
• Responses are truncated to ~50KB to stay within LLM context limits
• Errors (429, 5xx) trigger automatic retries with exponential backoff (up to 3 retries)

Claude Desktop Integration

Add any API to Claude Desktop by editing your config file:

Location:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

Public API (no auth)

{
  "mcpServers": {
    "petstore": {
      "command": "npx",
      "args": [
        "mcp-openapi",
        "--spec", "https://petstore3.swagger.io/api/v3/openapi.json"
      ]
    }
  }
}

API with Bearer Token

{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": [
        "mcp-openapi",
        "--spec", "https://raw.githubusercontent.com/github/rest-api-description/main/descriptions/api.github