---

name: typescript-mcp description: | Build stateless MCP servers with TypeScript on Cloudflare Workers using @modelcontextprotocol/sdk. Provides patterns for tools, resources, prompts, and authentication (API keys, OAuth, Zero Trust).

Use when exposing APIs to LLMs, integrating Cloudflare services (D1, KV, R2, Vectorize), or troubleshooting export syntax errors, unclosed transport leaks, or CORS misconfigurations. allowed-tools: [Read, Write, Edit, Bash, Grep, Glob]

TypeScript MCP on Cloudflare Workers

Last Updated: 2026-01-06 Versions: @modelcontextprotocol/sdk@1.25.1, hono@4.11.3, zod@3.24.2 Spec Version: 2025-11-25

---

Quick Start

npm install @modelcontextprotocol/sdk@latest hono zod
npm install -D @cloudflare/workers-types wrangler typescript

Basic MCP Server:

import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
import { Hono } from 'hono';
import { z } from 'zod';

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

server.registerTool(
  'echo',
  {
    description: 'Echoes back input',
    inputSchema: z.object({ text: z.string() })
  },
  async ({ text }) => ({ content: [{ type: 'text', text }] })
);

const app = new Hono();

app.post('/mcp', async (c) => {
  const transport = new StreamableHTTPServerTransport({
    sessionIdGenerator: undefined,
    enableJsonResponse: true
  });

  // CRITICAL: Close transport to prevent memory leaks
  c.res.raw.on('close', () => transport.close());

  await server.connect(transport);
  await transport.handleRequest(c.req.raw, c.res.raw, await c.req.json());
  return c.body(null);
});

export default app; // CRITICAL: Direct export, not { fetch: app.fetch }

Deploy: wrangler deploy

---

Authentication

API Key (KV-based):

app.use('/mcp', async (c, next) => {
  const apiKey = c.req.header('Authorization')?.replace('Bearer ', '');
  const isValid = await c.env.MCP_API_KEYS.get(`key:${apiKey}`);
  if (!isValid) return c.json({ error: 'Unauthorized' }, 403);
  await next();
});

Cloudflare Zero Trust:

const jwt = c.req.header('Cf-Access-Jwt-Assertion');
const payload = await verifyJWT(jwt, c.env.CF_ACCESS_TEAM_DOMAIN);

---

Tasks (v1.24.0+)

Tasks enable long-running operations that return a handle for polling results later. Useful for expensive computations, batch processing, or operations that may need input.

Task States: working → input_required → completed / failed / cancelled

Server Capability Declaration:

const server = new McpServer({
  name: 'my-server',
  version: '1.0.0',
  capabilities: {
    tasks: {
      list: {},
      cancel: {},
      requests: {
        tools: { call: {} }
      }
    }
  }
});

Tool with Task Support:

server.registerTool(
  'long-running-analysis',
  {
    description: 'Analyze large dataset',
    inputSchema: z.object({ datasetId: z.string() }),
    execution: { taskSupport: 'optional' }  // 'forbidden' | 'optional' | 'required'
  },
  async ({ datasetId }, extra) => {
    // If invoked as task, extra.task contains taskId
    const result = await performAnalysis(datasetId);
    return { content: [{ type: 'text', text: JSON.stringify(result) }] };
  }
);

Client Task Request:

{
  "method": "tools/call",
  "params": {
    "name": "long-running-analysis",
    "arguments": { "datasetId": "abc123" },
    "task": { "ttl": 60000 }
  }
}

Task Lifecycle:

1. Client sends request with task param → receives taskId
2. Client polls via tasks/get with taskId
3. When status is completed, client calls tasks/result to get output
4. Optional: Client can tasks/cancel to abort

📚 Spec: https://modelcontextprotocol.io/specification/2025-11-25/basic/utilities/tasks

---

Sampling with Tools (v1.24.0+)

Servers can now include tool definitions in sampling requests, enabling server-side agent loops.

Use Case: Server needs to orchestrate multi-step reasoning using LLM + tools without custom frameworks.

// Server initiates sampling with tools available
const result = await server.requestSampling({
  messages: [{ role: 'user', content: 'Analyze this data and fetch more if needed' }],
  maxTokens: 4096,
  tools: [
    {
      name: 'fetch_data',
      description: 'Fetch additional data from API',
      inputSchema: { type: 'object', properties: { query: { type: 'string' } } }
    }
  ]
});

// Handle tool calls in response
if (result.content[0].type === 'tool_use') {
  const toolResult = await executeLocalTool(result.content[0]);
  // Continue conversation with tool result...
}

Key Points:

• Server-side agentic behavior as first-class MCP feature
• Standard MCP primitives (no custom frameworks)
• Tool definitions follow same schema as tools/list

📚 Spec: SEP-1577

---

Cloudflare Service Tools

D1 Database:

server.registerTool('query-db', {
  inputSchema: z.object({ query: z.string(), params: z.array(z.union([z.string(), z.number()])).optional() })
}, async ({ query, params }, env) => {
  const result = await env.DB.prepare(query).bind(...(params || [])).all();
  return { content: [{ type: 'text', text: JSON.stringify(result.results) }] };
});

KV, R2, Vectorize: See references/cloudflare-integration.md

---

Known Issues Prevention

This skill prevents 10+ production issues documented in official MCP SDK and Cloudflare repos:

Issue #1: Export Syntax Issues (CRITICAL)

Error: "Cannot read properties of undefined (reading 'map')" Source: honojs/hono#3955, honojs/vite-plugins#237 Why It Happens: Incorrect export format with Vite build causes cryptic errors Prevention:

// ❌ WRONG - Causes cryptic build errors
export default { fetch: app.fetch };

// ✅ CORRECT - Direct export
export default app;

Issue #2: Unclosed Transport Connections

Error: Memory leaks, hanging connections Source: Best practice from SDK maintainers Why It Happens: Not closing StreamableHTTPServerTransport on request end Prevention:

app.post('/mcp', async (c) => {
  const transport = new StreamableHTTPServerTransport(/*...*/);

  // CRITICAL: Always close on response end
  c.res.raw.on('close', () => transport.close());

  // ... handle request
});

Issue #3: Tool Schema Validation Failure

Error: ListTools request handler fails to generate inputSchema Source: GitHub modelcontextprotocol/typescript-sdk#1028 Why It Happens: Zod schemas not properly converted to JSON Schema Prevention:

// ✅ CORRECT - SDK handles Zod schema conversion automatically
server.registerTool(
  'tool-name',
  {
    inputSchema: z.object({ a: z.number() })
  },
  handler
);

// No need for manual zodToJsonSchema() unless custom validation

Issue #4: Tool Arguments Not Passed to Handler

Error: Handler receives undefined arguments Source: GitHub modelcontextprotocol/typescript-sdk#1026 Why It Happens: Schema type mismatch between registration and invocation Prevention:

const schema = z.object({ a: z.number(), b: z.number() });
type Input = z.infer<typeof schema>;

server.registerTool(
  'add',
  { inputSchema: schema },
  async (args: Input) => {
    // args.a and args.b properly typed and passed
    return { content: [{ type: 'text', text: String(args.a + args.b) }] };
  }
);

Issue #5: CORS Misconfiguration

Error: Browser clients can't connect to MCP server Source: Common production issue Why It Happens: Missing CORS headers for HTTP transport Prevention:

import { cors } from 'hono/cors';

app.use('/mcp', cors({
  origin: ['http://localhost:3000', 'https://your-app.com'],
  allowMethods: ['POST', 'OPTIONS'],
  allowHeaders: ['Content-Type', 'Authorization']
}));

Issue #6: Missing Rate Limiting

Error: API abuse, DDoS vulnerability Source: Production security best practice Why It Happens: No rate limiting on MCP endpoints Prevention:

app.post('/mcp', async (c) => {
  const ip = c.req.header('CF-Connecting-IP');
  const rateLimitKey = `ratelimit:${ip}`;

  const count = await c.env.CACHE.get(rateLimitKey);
  if (count && parseInt(count) > 100) {
    return c.json({ error: 'Rate limit exceeded' }, 429);
  }

  await c.env.CACHE.put(
    rateLimitKey,
    String((parseInt(count || '0') + 1)),
    { expirationTtl: 60 }
  );

  // Continue...
});

Issue #7: TypeScript Compilation Memory Issues

Error: Out of memory during tsc build Source: GitHub modelcontextprotocol/typescript-sdk#985 Why It Happens: Large dependency tree in MCP SDK Prevention:

# Add to package.json scripts
"build": "NODE_OPTIONS='--max-old-space-size=4096' tsc && vite build"

Issue #8: UriTemplate ReDoS Vulnerability

Error: Server hangs on malicious URI patterns Source: GitHub modelcontextprotocol/typescript-sdk#965 (Security) Why It Happens: Regex denial-of-service in URI template parsing Prevention: Update to SDK v1.20.2 or later (includes fix)

Issue #9: Authentication Bypass

Error: Unauthenticated access to MCP tools Source: Production security best practice Why It Happens: Missing or improperly implemented authentication Prevention: Always implement authentication for production servers (see Authentication Patterns section)

Issue #10: Environment Variable Leakage

Error: Secrets exposed in error messages or logs Source: Cloudflare Workers security best practice Why It Happens: Environment variables logged or returned in responses Prevention:

// ❌ WRONG - Exposes secrets
console.log('Env:', JSON.stringify(env));

// ✅ CORRECT - Never log env objects
try {
  // ... use env.SECRET_KEY
} catch (error) {
  // Don't include env in error context
  console.error('Operation failed:', error.message);
}

---

Deployment

# Local
wrangler dev  # http://localhost:8787/mcp

# Production
wrangler deploy

Testing: npx @modelcontextprotocol/inspector (connect to http://localhost:8787/mcp)

---

Templates & References

Templates: basic-mcp-server.ts, tool-server.ts, resource-server.ts, authenticated-server.ts, tasks-server.ts, wrangler.jsonc

References: tool-patterns.md, authentication-guide.md, testing-guide.md, cloudflare-integration.md, common-errors.md

---

Critical Rules

Always:

• ✅ Close transport on response end (c.res.raw.on('close', () => transport.close()))
• ✅ Use direct export (export default app, NOT { fetch: app.fetch })
• ✅ Implement authentication for production
• ✅ Update to SDK v1.25.1+ for security fixes and Tasks support

Never:

• ❌ Export with object wrapper
• ❌ Forget to close StreamableHTTPServerTransport
• ❌ Log environment variables or secrets
• ❌ Use outdated SDK versions (<1.20.2 has ReDoS vulnerability)