MCP Protocol Design

MCP Protocol Design

Setup (TypeScript)

import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
import express from 'express';

const app = express();
app.use(express.json({ limit: '50mb' }));

// Stateless: new server per request (recommended for HTTP)
app.all('/mcp', async (req, res) => {
  const server = createMcpServer();
  const transport = new StreamableHTTPServerTransport({
    sessionIdGenerator: undefined,  // stateless
    enableJsonResponse: true,
  });
  res.on('close', () => transport.close());
  await server.connect(transport);
  await transport.handleRequest(req, res, req.body);
});

Tool Registration

function createMcpServer() {
  const server = new McpServer({ name: 'my-server', version: '1.0.0' });

  server.registerTool('my_tool', {
    title: 'My Tool',
    description: 'What this tool does and when to use it.',
    inputSchema: z.object({
      input: z.string().describe('The input to process'),
    }),
  }, async ({ input }) => {
    return { content: [{ type: 'text', text: `Result: ${input}` }] };
  });

  return server;
}

Health Endpoint (always add one)

app.get('/health', (_req, res) => res.json({
  ok: true, server: 'my-mcp', version: '1.0.0', uptime: process.uptime()
}));

MCP Client (connecting to an MCP server)

// From an orchestrator, calling an MCP tool over HTTP
const response = await fetch('http://localhost:3003/mcp', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    jsonrpc: '2.0', id: 1, method: 'tools/call',
    params: { name: 'claude_task', arguments: { task: 'Summarize this' } }
  })
});

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