What is Mcp It

mcp-it is a Fastify plugin that automatically generates Model Context Protocol (MCP) tools from your Fastify API routes, allowing AI assistants to interact with your API directly through the MCP protocol.

Use cases

Use cases for mcp-it include building APIs that need to be easily accessible by AI tools, creating automated documentation for API endpoints, and enhancing the interactivity of applications through AI-driven features.

How to use

To use mcp-it, install the package via npm or yarn, then register the plugin in your Fastify application. Define your routes with appropriate schemas and operation IDs to expose them as MCP tools.

Key features

Key features of mcp-it include automatic discovery of Fastify routes, generation of complete tool definitions leveraging Fastify’s schema system, and potential future support for adapters for other Node.js frameworks.

Where to use

mcp-it can be used in any application that utilizes Fastify as its web framework, particularly in scenarios where integration with AI assistants is desired.

@mcp-it/fastify

🤖 Automatically generate MCP tools from your Fastify API routes.

A Fastify plugin (@mcp-it/fastify) for the Model Context Protocol (MCP) that allows you to expose your Fastify routes as MCP tools. This enables AI assistants to interact with your API directly through the MCP protocol.

Overview

This plugin automatically discovers your Fastify routes and exposes them as tools consumable by MCP clients like Cursor or Claude. It leverages Fastify’s schema system to generate complete tool definitions.

[!NOTE]
While this package focuses specifically on Fastify, the @mcp-it scope may host adapters for other Node.js frameworks (like Express, NestJS, etc.) in the future.

Installation

npm install @mcp-it/fastify
# or
yarn add @mcp-it/fastify
# or
pnpm add @mcp-it/fastify

Usage

import Fastify from "fastify";
import mcpPlugin from "@mcp-it/fastify";

const fastify = Fastify();

// Register the MCP plugin
await fastify.register(mcpPlugin, {
  name: "My API",
  description: "My API with MCP support",
});

// Define your routes with schemas and operation IDs
fastify.get(
  "/users/:id",
  {
    schema: {
      operationId: "get_user", // Used as the tool name
      summary: "Get user by ID",
      description: "Returns a user by their ID",
      params: {
        type: "object",
        required: ["id"],
        properties: {
          id: { type: "number", description: "User ID" },
        },
      },
      response: {
        200: {
          description: "Successful response",
          type: "object",
          properties: {
            id: { type: "number" },
            name: { type: "string" },
            email: { type: "string" },
          },
        },
      },
    },
    // Add MCP-specific config if needed, e.g.:
    // config: {
    //   mcp: { hidden: true }
    // }
  },
  async (request) => {
    // Implementation...
    const userId = (request.params as any).id;
    // ... fetch user
    return { id: userId, name: "Example User", email: "[email protected]" };
  }
);

await fastify.listen({ port: 3000 });

console.log("MCP SSE server running at http://localhost:3000/mcp/sse");

Features

• Automatic Route Discovery: Utilizes Fastify hooks to identify all registered routes.
• Schema Utilization: Employs Fastify route schemas for comprehensive tool generation.
• Per-Route Configurations: Allows customization on a per-route basis.
• Multiple Transports: Supports both Server-Sent Events and Streamable HTTP transports.
• Debug Endpoint: An optional endpoint to view generated tools, independent of transport.

Configuration Options

Route Configuration (config.mcp)

You can add specific MCP configurations directly within a route’s config object. The following options are available:

Example usage:

fastify.get(
  "/some-route",
  {
    config: {
      mcp: {
        name: "custom_tool_name", // Override the default tool name
        description: "Custom description for this tool", // Override the default description
      },
    },
    // ... other route options
  },
  async (request, reply) => {
    /* ... */
  }
);

Accessing the MCP Server Instance

This plugin decorates the Fastify instance with the underlying MCP Server instance from @modelcontextprotocol/sdk. You can access it via fastify.mcpServer after the plugin has been registered.

This might be useful for advanced scenarios, such as:

• Directly interacting with the MCP server’s lifecycle or methods.
• Adding custom request handlers or capabilities beyond basic tool exposure.

import Fastify from "fastify";
import mcpPlugin from "@mcp-it/fastify";
import type { Server } from "@modelcontextprotocol/sdk/server/index.js";

const fastify = Fastify();

await fastify.register(mcpPlugin, {
  /* options */
});

// Now you can access the MCP server instance
console.log("MCP Server:", fastify.mcpServer);

// Example: Add a custom handler (use with caution)
// fastify.mcpServer.setRequestHandler(...);

// ... rest of your application setup

await fastify.listen({ port: 3000 });

Examples

See the examples directory for complete working examples demonstrating various features.

Client Configuration

Cursor

In Cursor settings (Settings -> MCP), add a new SSE connection with the URL:

http://localhost:3000/mcp/sse

(Replace localhost:3000 with your server’s address and mcp with your mountPath if customized).

Claude Desktop

Use mcp-proxy to bridge between Claude Desktop (which expects stdio) and the SSE endpoint.

Add the following to your Claude Desktop MCP config file (claude_desktop_config.json):

{
  "mcpServers": {
    "my-fastify-api": {
      "command": "npx",
      "args": [
        "mcp-remote",
        "http://localhost:3000/mcp/sse"
      ]
    }
  }
}

(Replace localhost:3000 with your server’s address and mcp with your mountPath if customized).

Alternatively, you can use the Streamable HTTP endpoint if your client supports it (Cursor might require configuration or proxying for non-SSE endpoints).