API Caller MCP Server

MCP (Model Context Protocol) Server: A service that enables calling external RESTful APIs.

Features

This MCP server provides tools for LLMs like Claude to call external RESTful APIs. It includes the following features:

• Support for various HTTP methods (GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS)
• Configurable headers, query parameters, and request body data
• Configurable timeout settings
• Error handling and response formatting

Installation and Execution

Requirements

• Node.js 16.x or higher
• npm or yarn

Installation

# Install dependencies
npm install

Build

# Compile TypeScript
npm run build

Execution

# Run StdIO version (integrated with MCP clients like Claude Desktop)
npm start

# Run HTTP server version (exposed as API)
npm run start:http

# Run in development mode (direct TypeScript execution)
npm run dev

# Run HTTP server in development mode
npm run dev:http

# Run in watch mode (useful during development)
npm run watch

# Run test client
npm run test

Adding MCP Server to Claude Desktop

1. Configure claude_desktop_config.json

Configure the claude_desktop_config.json file as follows. Use npx to run with dependency installation:

{
  "name": "API Caller",
  "version": "1.0.0",
  "description": "MCP service for calling external RESTful APIs",
  "command": "npx",
  "args": ["--yes", "--package=dotenv", "--package=axios", "--package=@modelcontextprotocol/sdk", "node", "{your_mcp_path}/api_caller/index.js"],
  "env": {
    "NODE_ENV": "production"
  }
}

Alternative Configuration Options:

1. Using Batch File (Recommended):

{
  "name": "API Caller",
  "version": "1.0.0",
  "description": "MCP service for calling external RESTful APIs",
  "command": "{your_mcp_path}/api_caller/run_with_npx.bat",
  "args": [],
  "env": {
    "NODE_ENV": "production"
  }
}

2. Using npm Script:

{
  "name": "API Caller",
  "version": "1.0.0",
  "description": "MCP service for calling external RESTful APIs",
  "command": "npx",
  "args": ["--yes", "npm", "run", "start"],
  "env": {
    "NODE_ENV": "production"
  }
}

Important: Ensure that file paths match the absolute path of your project folder.

2. Add MCP Provider to Claude Desktop

1. Launch Claude Desktop: Start the Claude Desktop application.

2. Open Settings Menu:

   • Click the profile icon or settings icon in the bottom left of the Claude Desktop window.
   • Select "Settings" from the menu.

3. Navigate to MCP Providers Tab:

   • Find and click on "MCP Providers" or "Tools" tab in the settings menu.

4. Add New MCP Provider:

   • Click "Add New MCP Provider" or the "+" button.

5. Select Configuration File:

   • In the file selection dialog, navigate to the claude_desktop_config.json file.
   • Path: {your_mcp_path}/api_caller/claude_desktop_config.json
   • Select this file and click "Open".

6. Enable MCP Provider:

   • Once API Caller is added to the list, toggle the switch next to it to enable.

3. Troubleshooting

If you encounter connection issues:

1. Check Dependencies:

   npm install
   

2. Verify Path Settings:

   • Ensure all file paths are correctly configured.
   • When using batch file method, verify run_with_npx.bat exists.

3. Permission Issues:

   • Run command prompt as administrator.

4. Check Logs:

   • Check Claude Desktop logs for error messages.
   • Run batch file directly to check for error messages.

5. Verify npx Installation:

   npm install -g npx
   

6. Module Format Issues:

   • If module format issues occur (CommonJS vs ES modules), check "type": "module" setting in package.json.

Usage

First, clone the repository:

git clone https://github.com/g2developer/api_caller_mcp_server.git
cd api_caller_mcp_server

This MCP server can be used with LLM clients that support the Model Context Protocol.

StdIO Interface

Register this server as an MCP provider in clients like Claude Desktop.

HTTP Interface

The HTTP server version provides the following endpoints:

• POST /mcp: Handles requests from MCP clients to the server.
• GET /mcp: Sends notifications from server to client via SSE (Server-Sent Events).
• DELETE /mcp: Terminates the session.
• GET /health: Checks server status.

Use mcp-session-id header for session management.

call_api Tool

Calls external RESTful APIs.

Parameters:

• url (required): URL of the API to call
• method (optional, default: GET): HTTP method (GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS)
• headers (optional): Request headers (API keys, auth tokens, etc.)
• params (optional): URL query parameters
• data (optional): Request body data (for POST, PUT, PATCH)
• timeout (optional, default: 30000): Request timeout in milliseconds

Return Value:

Success:

{
  "status": "success",
  "statusCode": 200,
  "headers": { ... },
  "data": { ... }
}

Failure:

{
  "status": "error",
  "message": "Error message",
  "statusCode": 404,
  "headers": { ... },
  "data": { ... }
}

Examples

Basic GET Request

{
  "url": "https://jsonplaceholder.typicode.com/posts/1"
}

GET Request with Query Parameters

{
  "url": "https://jsonplaceholder.typicode.com/posts",
  "params": {
    "userId": 1
  }
}

POST Request with Data

{
  "url": "https://jsonplaceholder.typicode.com/posts",
  "method": "POST",
  "headers": {
    "Content-Type": "application/json"
  },
  "data": {
    "title": "foo",
    "body": "bar",
    "userId": 1
  }
}

Request with Authentication Header

{
  "url": "https://api.example.com/data",
  "headers": {
    "Authorization": "Bearer your_token_here"
  }
}

Environment Variables

Configure the following environment variables in .env file:

• PORT: Port number for HTTP server (default: 3071)
• NODE_ENV: Execution environment (development, production, test)
• DEFAULT_TIMEOUT: Default API call timeout in milliseconds
• LOG_LEVEL: Logging level (debug, info, warn, error)
• DEFAULT_API_KEY: Default API key (if needed)
• DEFAULT_AUTH_TOKEN: Default authentication token (if needed)
• ALLOW_ORIGIN: CORS settings (default: *)

License

MIT License