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Build MCP servers with the Agents SDK

Apr 07, 2025, 01:00 PM

Agents Workers

The Agents SDK now includes built-in support for building remote MCP (Model Context Protocol) servers directly as part of your Agent. This allows you to easily create and manage MCP servers, without the need for additional infrastructure or configuration.

The SDK includes a new MCPAgent class that extends the Agent class and allows you to expose resources and tools over the MCP protocol, as well as authorization and authentication to enable remote MCP servers.

JavaScript

export class MyMCP extends McpAgent {
  server = new McpServer({
    name: "Demo",
    version: "1.0.0",
  });

  async init() {
    this.server.resource(`counter`, `mcp://resource/counter`, (uri) => {
      // ...
    });

    this.server.tool(
      "add",
      "Add two numbers together",
      { a: z.number(), b: z.number() },
      async ({ a, b }) => {
        // ...
      },
    );
  }
}

TypeScript

export class MyMCP extends McpAgent<Env> {
  server = new McpServer({
    name: "Demo",
    version: "1.0.0",
  });

  async init() {
    this.server.resource(`counter`, `mcp://resource/counter`, (uri) => {
      // ...
    });

    this.server.tool(
      "add",
      "Add two numbers together",
      { a: z.number(), b: z.number() },
      async ({ a, b }) => {
        // ...
      },
    );
  }
}

See the example ↗ for the full code and as the basis for building your own MCP servers, and the client example ↗ for how to build an Agent that acts as an MCP client.

To learn more, review the announcement blog ↗ as part of Developer Week 2025.

Agents SDK updates

We've made a number of improvements to the Agents SDK, including:

• Support for building MCP servers with the new MCPAgent class.
• The ability to export the current agent, request and WebSocket connection context using import { context } from "agents", allowing you to minimize or avoid direct dependency injection when calling tools.
• Fixed a bug that prevented query parameters from being sent to the Agent server from the useAgent React hook.
• Automatically converting the agent name in useAgent or useAgentChat to kebab-case to ensure it matches the naming convention expected by routeAgentRequest.

To install or update the Agents SDK, run npm i agents@latest in an existing project, or explore the agents-starter project:

npm create cloudflare@latest -- --template cloudflare/agents-starter

See the full release notes and changelog on the Agents SDK repository ↗ and