Building MCP Servers on Cloudflare

Your knowledge of the MCP SDK and Cloudflare Workers integration may be outdated. Prefer retrieval over pre-training for any MCP server task.

Retrieval Sources

Source How to retrieve Use for

MCP docs https://developers.cloudflare.com/agents/mcp/

Server setup, auth, deployment

MCP spec https://modelcontextprotocol.io/

Protocol spec, tool/resource definitions

Workers docs Search tool or https://developers.cloudflare.com/workers/

Runtime APIs, bindings, config

When to Use

• User wants to build a remote MCP server

• User needs to expose tools via MCP

• User asks about MCP authentication or OAuth

• User wants to deploy MCP to Cloudflare Workers

Prerequisites

• Cloudflare account with Workers enabled

• Node.js 18+ and npm/pnpm/yarn

• Wrangler CLI (npm install -g wrangler )

Quick Start

Option 1: Public Server (No Auth)

npm create cloudflare@latest -- my-mcp-server
--template=cloudflare/ai/demos/remote-mcp-authless cd my-mcp-server npm start

Server runs at http://localhost:8788/mcp

Option 2: Authenticated Server (OAuth)

npm create cloudflare@latest -- my-mcp-server
--template=cloudflare/ai/demos/remote-mcp-github-oauth cd my-mcp-server

Requires OAuth app setup. See references/oauth-setup.md.

Core Workflow

Step 1: Define Tools

Tools are functions MCP clients can call. Define them using server.tool() :

import { McpAgent } from "agents/mcp"; import { z } from "zod";

export class MyMCP extends McpAgent { server = new Server({ name: "my-mcp", version: "1.0.0" });

async init() { // Simple tool with parameters this.server.tool( "add", { a: z.number(), b: z.number() }, async ({ a, b }) => ({ content: [{ type: "text", text: String(a + b) }], }) );

// Tool that calls external API
this.server.tool(
  "get_weather",
  { city: z.string() },
  async ({ city }) => {
    const response = await fetch(`https://api.weather.com/${city}`);
    const data = await response.json();
    return {
      content: [{ type: "text", text: JSON.stringify(data) }],
    };
  }
);

} }

Step 2: Configure Entry Point

Public server (src/index.ts ):

import { MyMCP } from "./mcp";

export default { fetch(request: Request, env: Env, ctx: ExecutionContext) { const url = new URL(request.url); if (url.pathname === "/mcp") { return MyMCP.serveSSE("/mcp").fetch(request, env, ctx); } return new Response("MCP Server", { status: 200 }); }, };

export { MyMCP };

Authenticated server — See references/oauth-setup.md.

Step 3: Test Locally

Start server

npm start

In another terminal, test with MCP Inspector

npx @modelcontextprotocol/inspector@latest

Open http://localhost:5173, enter http://localhost:8788/mcp

Step 4: Deploy

npx wrangler deploy

Server accessible at https://[worker-name].[account].workers.dev/mcp

Step 5: Connect Clients

Claude Desktop (claude_desktop_config.json ):

{ "mcpServers": { "my-server": { "command": "npx", "args": ["mcp-remote", "https://my-mcp.workers.dev/mcp"] } } }

Restart Claude Desktop after updating config.

Tool Patterns

Return Types

// Text response return { content: [{ type: "text", text: "result" }] };

// Multiple content items return { content: [ { type: "text", text: "Here's the data:" }, { type: "text", text: JSON.stringify(data, null, 2) }, ], };

Input Validation with Zod

this.server.tool( "create_user", { email: z.string().email(), name: z.string().min(1).max(100), role: z.enum(["admin", "user", "guest"]), age: z.number().int().min(0).optional(), }, async (params) => { // params are fully typed and validated } );

Accessing Environment/Bindings

export class MyMCP extends McpAgent<Env> { async init() { this.server.tool("query_db", { sql: z.string() }, async ({ sql }) => { // Access D1 binding const result = await this.env.DB.prepare(sql).all(); return { content: [{ type: "text", text: JSON.stringify(result) }] }; }); } }

Authentication

For OAuth-protected servers, see references/oauth-setup.md.

Supported providers:

• GitHub

• Google

• Auth0

• Stytch

• WorkOS

• Any OAuth 2.0 compliant provider

Wrangler Configuration

Minimal wrangler.toml :

name = "my-mcp-server" main = "src/index.ts" compatibility_date = "2024-12-01"

[durable_objects] bindings = [{ name = "MCP", class_name = "MyMCP" }]

[[migrations]] tag = "v1" new_classes = ["MyMCP"]

With bindings (D1, KV, etc.):

[[d1_databases]] binding = "DB" database_name = "my-db" database_id = "xxx"

[[kv_namespaces]] binding = "KV" id = "xxx"

Common Issues

"Tool not found" in Client

• Verify tool name matches exactly (case-sensitive)

• Ensure init() registers tools before connections

• Check server logs: wrangler tail

Connection Fails

• Confirm endpoint path is /mcp

• Check CORS if browser-based client

• Verify Worker is deployed: wrangler deployments list

OAuth Redirect Errors

• Callback URL must match OAuth app config exactly

• Check GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET are set

• For local dev, use http://localhost:8788/callback

References

• references/examples.md — Official templates and production examples

• references/oauth-setup.md — OAuth provider configuration

• references/tool-patterns.md — Advanced tool examples

• references/troubleshooting.md — Error codes and fixes