building-mcp-server-on-cloudflare

name

building-mcp-server-on-cloudflare

description

Builds remote MCP (Model Context Protocol) servers on Cloudflare Workers with tools, OAuth authentication, and production deployment. Generates server code, configures auth providers, and deploys to Workers. Use when: user wants to "build MCP server", "create MCP tools", "remote MCP", "deploy MCP", add "OAuth to MCP", or mentions Model Context Protocol on Cloudflare. Also triggers on "MCP authentication" or "MCP deployment". Biases towards retrieval from Cloudflare docs over pre-trained knowledge.

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Your knowledge of the MCP SDK and Cloudflare Workers integration may be outdated.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

Codex MCP client setup:

codex mcp add my-server -- npx mcp-remote https://my-mcp.workers.dev/mcp

Restart Codex after updating the MCP configuration.

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

1. Verify tool name matches exactly (case-sensitive)
2. Ensure init() registers tools before connections
3. Check server logs: wrangler tail

Connection Fails

1. Confirm endpoint path is /mcp
2. Check CORS if browser-based client
3. Verify Worker is deployed: wrangler deployments list

OAuth Redirect Errors

1. Callback URL must match OAuth app config exactly
2. Check GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET are set
3. 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/troubleshooting.md — Error codes and fixes