MCP Server Adapters Example

This example demonstrates how to use MCP (Model Context Protocol) server endpoints with both Hono and Express server adapters.

What This Example Shows

Setting up MCP servers with tools
Integrating MCP servers with Mastra
Using the Hono adapter (@mastra/hono)
Using the Express adapter (@mastra/express)
Testing MCP endpoints via HTTP and SSE transports
Express.json() middleware compatibility with MCP routes

Setup

bash

pnpm install

Running the Servers

Hono Server (port 3001)

bash

pnpm start:hono

Express Server (port 3002)

bash

pnpm start:express

Testing MCP Endpoints

With a server running, run the test script:

bash

# Test Hono server (default port 3001)
pnpm test:mcp

# Test Express server (port 3002)
pnpm test:mcp -- --port 3002

MCP Endpoints

Each server exposes the following MCP endpoints:

HTTP Transport

POST /api/mcp/{serverId}/mcp - Stateless HTTP transport for MCP messages

SSE Transport

GET /api/mcp/{serverId}/sse - Establish SSE connection
POST /api/mcp/{serverId}/messages - Send messages to SSE session

Available Tools

Main Server

getWeather - Gets weather for a location
calculate - Performs basic math operations
echo - Echoes back a message

Secondary Server

calculate - Performs basic math operations

Using MCPClient

You can connect to these servers using @mastra/mcp's MCPClient:

typescript

import { MCPClient } from '@mastra/mcp';

const client = new MCPClient({
  servers: {
    main: {
      // Use 'main-mcp' as the serverId (matches the key in Mastra's mcpServers config)
      url: new URL('http://localhost:3001/api/mcp/main-mcp/mcp'),
    },
  },
});

// List available tools
const tools = await client.listTools();

// Execute a tool
const result = await tools['main_calculate'].execute({
  operation: 'multiply',
  a: 6,
  b: 7,
});

Express.json() Compatibility

The Express server demonstrates that MCP routes work correctly even when express.json() middleware is applied globally. The server adapter handles both pre-parsed request bodies (from middleware) and raw request streams.