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OpenAPI Integration

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MCP server exposing OpenAPI endpoints for LLMs to discover and interact with REST APIs.

OpenAPI MCP Server

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A Model Context Protocol (MCP) server that exposes OpenAPI endpoints as MCP resources. This server allows Large Language Models to discover and interact with REST APIs defined by OpenAPI specifications through the MCP protocol.

📖 Documentation

  • User Guide - For users wanting to use this MCP server with Claude Desktop, Cursor, or other MCP clients
  • Library Usage - For developers creating custom MCP servers using this package as a library
  • Developer Guide - For contributors and developers working on the codebase
  • AuthProvider Guide - Detailed authentication patterns and examples

User Guide

This section covers how to use the MCP server as an end user with Claude Desktop, Cursor, or other MCP-compatible tools.

Overview

This MCP server can be used in two ways:

  1. CLI Tool: Use npx @ivotoby/openapi-mcp-server directly with command-line arguments for quick setup
  2. Library: Import and use the OpenAPIServer class in your own Node.js applications for custom implementations

The server supports two transport methods:

  1. Stdio Transport (default): For direct integration with AI systems like Claude Desktop that manage MCP connections through standard input/output.
  2. Streamable HTTP Transport: For connecting to the server over HTTP, allowing web clients and other HTTP-capable systems to use the MCP protocol.

Quick Start for Users

Option 1: Using with Claude Desktop (Stdio Transport)

No need to clone this repository. Simply configure Claude Desktop to use this MCP server:

  1. Locate or create your Claude Desktop configuration file:

    • On macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

  2. Add the following configuration:

{
  "mcpServers": {
    "openapi": {
      "command": "npx",
      "args": ["-y", "@ivotoby/openapi-mcp-server"],
      "env": {
        "API_BASE_URL": "https://api.example.com",
        "OPENAPI_SPEC_PATH": "https://api.example.com/openapi.json",
        "API_HEADERS": "Authorization:Bearer token123,X-API-Key:your-api-key"
      }
    }
  }
}
  1. Replace the environment variables with your actual API configuration:
    • API_BASE_URL: The base URL of your API
    • OPENAPI_SPEC_PATH: URL or path to your OpenAPI specification
    • API_HEADERS: Comma-separated key:value pairs for API authentication headers

Option 2: Using with HTTP Clients (HTTP Transport)

To use the server with HTTP clients:

  1. No installation required! Use npx to run the package directly:
npx @ivotoby/openapi-mcp-server \
  --api-base-url https://api.example.com \
  --openapi-spec https://api.example.com/openapi.json \
  --headers "Authorization:Bearer token123" \
  --transport http \
  --port 3000
  1. Interact with the server using HTTP requests:
# Initialize a session (first request)
curl -X POST http://localhost:3000/mcp \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"curl-client","version":"1.0.0"}}}'

# The response includes a Mcp-Session-Id header that you must use for subsequent requests
# and the InitializeResult directly in the POST response body.

# Send a request to list tools
# This also receives its response directly on this POST request.
curl -X POST http://localhost:3000/mcp \
  -H "Content-Type: application/json" \
  -H "Mcp-Session-Id: your-session-id" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

# Open a streaming connection for other server responses (e.g., tool execution results)
# This uses Server-Sent Events (SSE).
curl -N http://localhost:3000/mcp -H "Mcp-Session-Id: your-session-id"

# Example: Execute a tool (response will arrive on the GET stream)
# curl -X POST http://localhost:3000/mcp \
#  -H "Content-Type: application/json" \
#  -H "Mcp-Session-Id: your-session-id" \
#  -d '{"jsonrpc":"2.0","id":2,"method":"tools/execute","params":{"name":"yourToolName", "arguments": {}}}'

# Terminate the session when done
curl -X DELETE http://localhost:3000/mcp -H "Mcp-Session-Id: your-session-id"

Configuration Options

The server can be configured through environment variables or command line arguments:

Environment Variables

  • API_BASE_URL - Base URL for the API endpoints
  • OPENAPI_SPEC_PATH - Path or URL to OpenAPI specification
  • OPENAPI_SPEC_FROM_STDIN - Set to "true" to read OpenAPI spec from standard input
  • OPENAPI_SPEC_INLINE - Provide OpenAPI spec content directly as a string
  • API_HEADERS - Comma-separated key:value pairs for API headers
  • SERVER_NAME - Name for the MCP server (default: "mcp-openapi-server")
  • SERVER_VERSION - Version of the server (default: "1.0.0")
  • TRANSPORT_TYPE - Transport type to use: "stdio" or "http" (default: "stdio")
  • HTTP_PORT - Port for HTTP transport (default: 3000)
  • HTTP_HOST - Host for HTTP transport (default: "127.0.0.1")
  • ENDPOINT_PATH - Endpoint path for HTTP transport (default: "/mcp")
  • TOOLS_MODE - Tools loading mode: "all" (load all endpoint-based tools), "dynamic" (load only meta-tools), or "explicit" (load only tools specified in includeTools) (default: "all")
  • DISABLE_ABBREVIATION - Disable name optimization (this could throw errors when name is > 64 chars)

Command Line Arguments

npx @ivotoby/openapi-mcp-server \
  --api-base-url https://api.example.com \
  --openapi-spec https://api.example.com/openapi.json \
  --headers "Authorization:Bearer token123,X-API-Key:your-api-key" \
  --name "my-mcp-server" \
  --server-version "1.0.0" \
  --transport http \
  --port 3000 \
  --host 127.0.0.1 \
  --path /mcp \
  --disable-abbreviation true

OpenAPI Specification Loading

The MCP server supports multiple methods for loading OpenAPI specifications, providing flexibility for different deployment scenarios:

1. URL Loading (Default)

Load the OpenAPI spec from a remote URL:

npx @ivotoby/openapi-mcp-server \
  --api-base-url https://api.example.com \
  --openapi-spec https://api.example.com/openapi.json

2. Local File Loading

Load the OpenAPI spec from a local file:

npx @ivotoby/openapi-mcp-server \
  --api-base-url https://api.example.com \
  --openapi-spec ./path/to/openapi.yaml

3. Standard Input Loading

Read the OpenAPI spec from standard input (useful for piping or containerized environments):

# Pipe from file
cat openapi.json | npx @ivotoby/openapi-mcp-server \
  --api-base-url https://api.example.com \
  --spec-from-stdin

# Pipe from curl
curl -s https://api.example.com/openapi.json | npx @ivotoby/openapi-mcp-server \
  --api-base-url https://api.example.com \
  --spec-from-stdin

# Using environment variable
export OPENAPI_SPEC_FROM_STDIN=true
echo '{"openapi": "3.0.0", ...}' | npx @ivotoby/openapi-mcp-server \
  --api-base-url https://api.example.com

4. Inline Specification

Provide the OpenAPI spec content directly as a command line argument:

npx @ivotoby/openapi-mcp-server \
  --api-base-url https://api.example.com \
  --spec-inline '{"openapi": "3.0.0", "info": {"title": "My API", "version": "1.0.0"}, "paths": {}}'

# Using environment variable
export OPENAPI_SPEC_INLINE='{"openapi": "3.0.0", ...}'
npx @ivotoby/openapi-mcp-server --api-base-url https://api.example.com

Supported Formats

All loading methods support both JSON and YAML formats. The server automatically detects the format and parses accordingly.

Docker and Container Usage

For containerized deployments, you can mount OpenAPI specs or use stdin:

# Mount local file
docker run -v /path/to/spec:/app/spec.json your-mcp-server \
  --api-base-url https://api.example.com \
  --openapi-spec /app/spec.json

# Use stdin with docker
cat openapi.json | docker run -i your-mcp-server \
  --api-base-url https://api.example.com \
  --spec-from-stdin

Error Handling

The server provides detailed error messages for spec loading failures:

  • URL loading: HTTP status codes and network errors
  • File loading: File system errors (not found, permissions, etc.)
  • Stdin loading: Empty input or read errors
  • Inline loading: Missing content errors
  • Parsing errors: Detailed JSON/YAML syntax error messages

Validation

Only one specification source can be used at a time. The server will validate that exactly one of the following is provided:

  • --openapi-spec (URL or file path)
  • --spec-from-stdin
  • --spec-inline

If multiple sources are specified, the server will exit with an error message.

Tool Loading & Filtering Options

Based on the Stainless article "What We Learned Converting Complex OpenAPI Specs to MCP Servers" (https://www.stainless.com/blog/what-we-learned-converting-complex-openapi-specs-to-mcp-servers), the following flags were added to control which API endpoints (tools) are loaded:

  • --tools <all|dynamic|explicit>: Choose tool loading mode:
    • all (default): Load all tools from the OpenAPI spec, applying any specified filters
    • dynamic: Load only dynamic meta-tools (list-api-endpoints, get-api-endpoint-schema, invoke-api-endpoint)
    • explicit: Load only tools explicitly listed in --tool options, ignoring all other filters
  • --tool <toolId>: Import only specified tool IDs or names. Can be used multiple times.
  • --tag <tag>: Import only tools with the specified OpenAPI tag. Can be used multiple times.
  • --resource <resource>: Import only tools under the specified resource path prefixes. Can be used multiple times.
  • --operation <method>: Import only tools for the specified HTTP methods (get, post, etc). Can be used multiple times.

Examples:

# Load only dynamic meta-tools
npx @ivotoby/openapi-mcp-server --api-base-url https://api.example.com --openapi-spec https://api.example.com/openapi.json --tools dynamic

# Load only explicitly specified tools (ignores other filters)
npx @ivotoby/openapi-mcp-server --api-base-url https://api.example.com --openapi-spec https://api.example.com/openapi.json --tools explicit --tool GET::users --tool POST::users

# Load only the GET /users endpoint tool (using all mode with filtering)
npx @ivotoby/openapi-mcp-server --api-base-url https://api.example.com --openapi-spec https://api.example.com/openapi.json --tool GET-users

# Load tools tagged with "user" under the "/users" resource
npx @ivotoby/openapi-mcp-server --api-base-url https://api.example.com --openapi-spec https://api.example.com/openapi.json --tag user --resource users

# Load only POST operations
npx @ivotoby/openapi-mcp-server --api-base-url https://api.example.com --openapi-spec https://api.example.com/openapi.json --operation post

Transport Types

Stdio Transport (Default)

The stdio transport is designed for direct integration with AI systems like Claude Desktop that manage MCP connections through standard input/output. This is the simplest setup and requires no network configuration.

When to use: When integrating with Claude Desktop or other systems that support stdio-based MCP communication.

Streamable HTTP Transport

The HTTP transport allows the MCP server to be accessed over HTTP, enabling web applications and other HTTP-capable clients to interact with the MCP protocol. It supports session management, streaming responses, and standard HTTP methods.

Key features:

  • Session management with Mcp-Session-Id header
  • HTTP responses for initialize and tools/list requests are sent synchronously on the POST.
  • Other server-to-client messages (e.g., tools/execute results, notifications) are streamed over a GET connection using Server-Sent Events (SSE).
  • Support for POST/GET/DELETE methods

When to use: When you need to expose the MCP server to web clients or systems that communicate over HTTP rather than stdio.

Security Considerations

  • The HTTP transport validates Origin headers to prevent DNS rebinding attacks
  • By default, HTTP transport only binds to localhost (127.0.0.1)
  • If exposing to other hosts, consider implementing additional authentication

Debugging

To see debug logs:

  1. When using stdio transport with Claude Desktop:

    • Logs appear in the Claude Desktop logs

  2. When using HTTP transport:

    npx @ivotoby/openapi-mcp-server --transport http &2>debug.log

Library Usage

This section is for developers who want to use this package as a library to create custom MCP servers.

🚀 Using as a Library

Create dedicated MCP servers for specific APIs by importing and configuring the OpenAPIServer class. This approach is ideal for:

  • Custom Authentication: Implement complex authentication patterns with the AuthProvider interface
  • API-Specific Optimizations: Filter endpoints, customize error handling, and optimize for specific use cases
  • Distribution: Package your server as a standalone npm module for easy sharing
  • Integration: Embed the server in larger applications or add custom middleware

Basic Library Usage

import { OpenAPIServer } from "@ivotoby/openapi-mcp-server"
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js"

const config = {
  name: "my-api-server",
  version: "1.0.0",
  apiBaseUrl: "https://api.example.com",
  openApiSpec: "https://api.example.com/openapi.json",
  specInputMethod: "url" as const,
  headers: {
    Authorization: "Bearer your-token",
    "X-API-Key": "your-api-key",
  },
  transportType: "stdio" as const,
  toolsMode: "all" as const, // Options: "all", "dynamic", "explicit"
}

const server = new OpenAPIServer(config)
const transport = new StdioServerTransport()
await server.start(transport)

Tool Loading Modes

The toolsMode configuration option controls which tools are loaded from your OpenAPI specification:

// Load all tools from the spec (default)
const config = {
  // ... other config
  toolsMode: "all" as const,
  // Optional: Apply filters to control which tools are loaded
  includeTools: ["GET::users", "POST::users"], // Only these tools
  includeTags: ["public"], // Only tools with these tags
  includeResources: ["users"], // Only tools under these resources
  includeOperations: ["get", "post"], // Only these HTTP methods
}

// Load only dynamic meta-tools for API exploration
const config = {
  // ... other config
  toolsMode: "dynamic" as const,
  // Provides: list-api-endpoints, get-api-endpoint-schema, invoke-api-endpoint
}

// Load only explicitly specified tools (ignores other filters)
const config = {
  // ... other config
  toolsMode: "explicit" as const,
  includeTools: ["GET::users", "POST::users"], // Only these exact tools
  // includeTags, includeResources, includeOperations are ignored in explicit mode
}

Advanced Authentication with AuthProvider

For APIs with token expiration, refresh requirements, or complex authentication:

import { OpenAPIServer, AuthProvider } from "@ivotoby/openapi-mcp-server"
import { AxiosError } from "axios"

class MyAuthProvider implements AuthProvider {
  async getAuthHeaders(): Promise<Record<string, string>> {
    // Called before each request - return fresh headers
    if (this.isTokenExpired()) {
      await this.refreshToken()
    }
    return { Authorization: `Bearer ${this.token}` }
  }

  async handleAuthError(error: AxiosError): Promise<boolean> {
    // Called on 401/403 errors - return true to retry
    if (error.response?.status === 401) {
      await this.refreshToken()
      return true // Retry the request
    }
    return false
  }
}

const authProvider = new MyAuthProvider()
const config = {
  // ... other config
  authProvider: authProvider, // Use AuthProvider instead of static headers
}

📁 See the examples/ directory for complete, runnable examples including:

  • Basic library usage with static authentication
  • AuthProvider implementations for different scenarios
  • Real-world Beatport API integration
  • Production-ready packaging patterns

🔐 Dynamic Authentication with AuthProvider

The AuthProvider interface enables sophisticated authentication scenarios that static headers cannot handle:

Key Features

  • Dynamic Headers: Fresh authentication headers for each request
  • Token Expiration Handling: Automatic detection and handling of expired tokens
  • Authentication Error Recovery: Retry logic for recoverable authentication failures
  • Custom Error Messages: Provide clear, actionable guidance to users

AuthProvider Interface

interface AuthProvider {
  /**
   * Get authentication headers for the current request
   * Called before each API request to get fresh headers
   */
  getAuthHeaders(): Promise<Record<string, string>>

  /**
   * Handle authentication errors from API responses
   * Called when the API returns 401 or 403 errors
   * Return true to retry the request, false otherwise
   */
  handleAuthError(error: AxiosError): Promise<boolean>
}

Common Patterns

Automatic Token Refresh

class RefreshableAuthProvider implements AuthProvider {
  async getAuthHeaders(): Promise<Record<string, string>> {
    if (this.isTokenExpired()) {
      await this.refreshToken()
    }
    return { Authorization: `Bearer ${this.accessToken}` }
  }

  async handleAuthError(error: AxiosError): Promise<boolean> {
    if (error.response?.status === 401) {
      await this.refreshToken()
      return true // Retry with fresh token
    }
    return false
  }
}

Manual Token Management (e.g., Beatport)

class ManualTokenAuthProvider implements AuthProvider {
  async getAuthHeaders(): Promise<Record<string, string>> {
    if (!this.token || this.isTokenExpired()) {
      throw new Error(
        "Token expired. Please get a new token from your browser:\n" +
          "1. Go to the API website and log in\n" +
          "2. Open browser dev tools (F12)\n" +
          "3. Copy the Authorization header from any API request\n" +
          "4. Update your token using updateToken()",
      )
    }
    return { Authorization: `Bearer ${this.token}` }
  }

  updateToken(token: string): void {
    this.token = token
    this.tokenExpiry = new Date(Date.now() + 3600000) // 1 hour
  }
}

API Key Authentication

class ApiKeyAuthProvider implements AuthProvider {
  constructor(private apiKey: string) {}

  async getAuthHeaders(): Promise<Record<string, string>> {
    return { "X-API-Key": this.apiKey }
  }

  async handleAuthError(error: AxiosError): Promise<boolean> {
    throw new Error("API key authentication failed. Please check your key.")
  }
}

📖 For detailed AuthProvider documentation and examples, see docs/auth-provider-guide.md

OpenAPI Schema Processing

Reference Resolution

This MCP server implements robust OpenAPI reference ($ref) resolution to ensure accurate representation of API schemas:

  • Parameter References: Fully resolves $ref pointers to parameter components in the OpenAPI spec
  • Schema References: Handles nested schema references within parameters and request bodies
  • Recursive References: Prevents infinite loops by detecting and handling circular references
  • Nested Properties: Preserves complex nested object and array structures with all their attributes

Input Schema Composition

The server intelligently merges parameters and request bodies into a unified input schema for each tool:

  • Parameters + Request Body Merging: Combines path, query, and body parameters into a single schema
  • Collision Handling: Resolves naming conflicts by prefixing body properties that conflict with parameter names
  • Type Preservation: Maintains the original type information for all schema elements
  • Metadata Retention: Preserves descriptions, formats, defaults, enums, and other schema attributes

Complex Schema Support

The MCP server handles various OpenAPI schema complexities:

  • Primitive Type Bodies: Wraps non-object request bodies in a "body" property
  • Object Bodies: Flattens object properties into the tool's input schema
  • Array Bodies: Properly handles array schemas with their nested item definitions
  • Required Properties: Tracks and preserves which parameters and properties are required

Developer Information

For Developers

Development Tools

  • npm run build - Builds the TypeScript source
  • npm run clean - Removes build artifacts
  • npm run typecheck - Runs TypeScript type checking
  • npm run lint - Runs ESLint
  • npm run dev - Watches source files and rebuilds on changes
  • npm run inspect-watch - Runs the inspector with auto-reload on changes

Development Workflow

  1. Clone the repository
  2. Install dependencies: npm install
  3. Start the development environment: npm run inspect-watch
  4. Make changes to the TypeScript files in src/
  5. The server will automatically rebuild and restart

Contributing

  1. Fork the repository
  2. Create a feature branch
  3. Make your changes
  4. Run tests and linting: npm run typecheck && npm run lint
  5. Submit a pull request

📖 For comprehensive developer documentation, see docs/developer-guide.md

FAQ

Q: What is a "tool"? A: A tool corresponds to a single API endpoint derived from your OpenAPI specification, exposed as an MCP resource.

Q: How can I use this package in my own project? A: You can import the OpenAPIServer class and use it as a library in your Node.js application. This allows you to create dedicated MCP servers for specific APIs with custom authentication, filtering, and error handling. See the examples/ directory for complete implementations.

Q: What's the difference between using the CLI and using it as a library? A: The CLI is great for quick setup and testing, while the library approach allows you to create dedicated packages for specific APIs, implement custom authentication with AuthProvider, add custom logic, and distribute your server as a standalone npm module.

Q: How do I handle APIs with expiring tokens? A: Use the AuthProvider interface instead of static headers. AuthProvider allows you to implement dynamic authentication with token refresh, expiration handling, and custom error recovery. See the AuthProvider examples for different patterns.

Q: What is AuthProvider and when should I use it? A: AuthProvider is an interface for dynamic authentication that gets fresh headers before each request and handles authentication errors. Use it when your API has expiring tokens, requires token refresh, or needs complex authentication logic that static headers can't handle.

Q: How do I filter which tools are loaded? A: Use the --tool, --tag, --resource, and --operation flags with --tools all (default), set --tools dynamic for meta-tools only, or use --tools explicit to load only tools specified with --tool (ignoring other filters).

Q: When should I use dynamic mode? A: Dynamic mode provides meta-tools (list-api-endpoints, get-api-endpoint-schema, invoke-api-endpoint) to inspect and interact with endpoints without preloading all operations, which is useful for large or changing APIs.

Q: How do I specify custom headers for API requests? A: Use the --headers flag or API_HEADERS environment variable with key:value pairs separated by commas for CLI usage. For library usage, use the headers config option or implement an AuthProvider for dynamic headers.

Q: Which transport methods are supported? A: The server supports stdio transport (default) for integration with AI systems and HTTP transport (with streaming via SSE) for web clients.

Q: How does the server handle complex OpenAPI schemas with references? A: The server fully resolves $ref references in parameters and schemas, preserving nested structures, default values, and other attributes. See the "OpenAPI Schema Processing" section for details on reference resolution and schema composition.

Q: What happens when parameter names conflict with request body properties? A: The server detects naming conflicts and automatically prefixes body property names with body_ to avoid collisions, ensuring all properties are accessible.

Q: Can I package my MCP server for distribution? A: Yes! When using the library approach, you can create a dedicated npm package for your API. See the Beatport example for a complete implementation that can be packaged and distributed as npx your-api-mcp-server.

Q: Where can I find development and contribution guidelines? A: See the Developer Guide for comprehensive documentation on architecture, key concepts, development workflow, and contribution guidelines.

License

MIT

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