Upgrade MCP SDK to v1.25.1

examples/mcp-server/README.md

@@ -0,0 +1,22 @@
+# MCP Server Example
+
+This example demonstrates how to use `WebStandardStreamableHTTPServerTransport` to create an unauthenticated stateless MCP server.
+
+In this example we do not use the `agents` package, but instead use the `@modelcontextprotocol/sdk` package directly to create an MCP server that "just works" on Cloudflare Workers.
+
+This is THE simplest way to get started with MCP on Cloudflare.
+
+## Usage
+
+```bash
+npm install
+npm run dev
+```
+
+## Testing
+
+You can test the MCP server using the MCP Inspector or any MCP client that supports the `streamable-http` transport.
+
+## Adding State
+
+To create a stateful MCP server, you can use an `Agent` to keep the state of the session/transport. See the [`mcp-elicitations`](../mcp-elicitation) example for more information.

examples/mcp-server/env.d.ts

@@ -0,0 +1,9 @@
+/* eslint-disable */
+// Generated by Wrangler by running `wrangler types env.d.ts --include-runtime false` (hash: b739a9c19cff1463949c4db47674ed86)
+declare namespace Cloudflare {
+  interface GlobalProps {
+    mainModule: typeof import("./src/index");
+  }
+  interface Env {}
+}
+interface Env extends Cloudflare.Env {}

examples/mcp-server/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "@cloudflare/agents-mcp-server",
+  "description": "zero config stateless MCP Server on Cloudflare",
+  "author": "Matt Carey <mcarey@cloudflare.com>",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "wrangler dev",
+    "deploy": "wrangler deploy",
+    "types": "wrangler types env.d.ts --include-runtime false"
+  }
+}

examples/mcp-server/src/index.ts

@@ -0,0 +1,54 @@
+import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { z } from "zod";
+import { WebStandardStreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/webStandardStreamableHttp.js";
+
+const server = new McpServer({
+  name: "Hello MCP Server",
+  version: "1.0.0"
+});
+
+server.registerTool(
+  "hello",
+  {
+    description: "Returns a greeting message",
+    inputSchema: { name: z.string().optional() }
+  },
+  async ({ name }) => {
+    return {
+      content: [
+        {
+          text: `Hello, ${name ?? "World"}!`,
+          type: "text"
+        }
+      ]
+    };
+  }
+);
+
+const transport = new WebStandardStreamableHTTPServerTransport();
+server.connect(transport);
+
+const corsHeaders = {
+  "Access-Control-Allow-Origin": "*",
+  "Access-Control-Allow-Methods": "GET, POST, DELETE, OPTIONS",
+  "Access-Control-Allow-Headers":
+    "Content-Type, Accept, mcp-session-id, mcp-protocol-version",
+  "Access-Control-Expose-Headers": "mcp-session-id",
+  "Access-Control-Max-Age": "86400"
+};
+
+function withCors(response: Response): Response {
+  for (const [key, value] of Object.entries(corsHeaders)) {
+    response.headers.set(key, value);
+  }
+  return response;
+}
+
+export default {
+  fetch: async (request: Request, _env: Env, _ctx: ExecutionContext) => {
+    if (request.method === "OPTIONS") {
+      return new Response(null, { headers: corsHeaders });
+    }
+    return withCors(await transport.handleRequest(request));
+  }
+};

examples/mcp-server/tsconfig.json

@@ -0,0 +1,3 @@
+{
+  "extends": "../../tsconfig.base.json"
+}

examples/mcp-server/wrangler.jsonc

@@ -0,0 +1,11 @@
+{
+  "compatibility_date": "2025-10-08",
+  "compatibility_flags": ["nodejs_compat"],
+  "main": "src/index.ts",
+  "name": "mcp-server",
+  "observability": {
+    "logs": {
+      "enabled": true
+    }
+  }
+}

examples/mcp-worker/README.md

@@ -2,8 +2,6 @@
 
 This example demonstrates how to use `createMcpHandler` to create an unauthenticated stateless MCP server.
 
-This is THE simplest way to get started with MCP on Cloudflare.
-
 ## Usage
 
 ```bash

package.json

@@ -37,7 +37,7 @@
     "@cloudflare/vite-plugin": "^1.19.0",
     "@cloudflare/vitest-pool-workers": "^0.11.1",
     "@cloudflare/workers-types": "^4.20251221.0",
-    "@modelcontextprotocol/sdk": "1.23.0",
+    "@modelcontextprotocol/sdk": "1.25.1",
     "@openai/agents": "^0.3.7",
     "@openai/agents-extensions": "^0.3.7",
     "@types/node": "^25.0.3",

packages/agents/package.json

@@ -25,7 +25,7 @@
   },
   "dependencies": {
     "@cfworker/json-schema": "^4.1.1",
-    "@modelcontextprotocol/sdk": "1.23.0",
+    "@modelcontextprotocol/sdk": "1.25.1",
     "cron-schedule": "^6.0.0",
     "json-schema": "^0.4.0",
     "json-schema-to-typescript": "^15.0.4",

packages/agents/src/mcp/errors.ts

@@ -2,14 +2,34 @@ export function toErrorMessage(error: unknown): string {
   return error instanceof Error ? error.message : String(error);
 }
 
+function getErrorCode(error: unknown): number | undefined {
+  if (
+    error &&
+    typeof error === "object" &&
+    "code" in error &&
+    typeof (error as { code: unknown }).code === "number"
+  ) {
+    return (error as { code: number }).code;
+  }
+  return undefined;
+}
+
 export function isUnauthorized(error: unknown): boolean {
+  const code = getErrorCode(error);
+  if (code === 401) return true;
+
   const msg = toErrorMessage(error);
   return msg.includes("Unauthorized") || msg.includes("401");
 }
 
+// MCP SDK change (v1.24.0, commit 6b90e1a):
+//   - Old: Error POSTing to endpoint (HTTP 404): Not Found
+//   - New: StreamableHTTPError with code: 404 and message Error POSTing to endpoint: Not Found
 export function isTransportNotImplemented(error: unknown): boolean {
+  const code = getErrorCode(error);
+  if (code === 404 || code === 405) return true;
+
   const msg = toErrorMessage(error);
-  // Treat common "not implemented" surfaces as transport not supported
   return (
     msg.includes("404") ||
     msg.includes("405") ||

packages/agents/src/mcp/index.ts

@@ -7,8 +7,8 @@ import type {
 } from "@modelcontextprotocol/sdk/types.js";
 import {
   JSONRPCMessageSchema,
-  isJSONRPCError,
-  isJSONRPCResponse,
+  isJSONRPCErrorResponse,
+  isJSONRPCResultResponse,
   type ElicitResult
 } from "@modelcontextprotocol/sdk/types.js";
 import type { Connection, ConnectionContext } from "../";
@@ -312,7 +312,7 @@ export abstract class McpAgent<
     message: JSONRPCMessage
   ): Promise<boolean> {
     // Check if this is a response to an elicitation request
-    if (isJSONRPCResponse(message) && message.result) {
+    if (isJSONRPCResultResponse(message) && message.result) {
       const requestId = message.id?.toString();
       if (!requestId || !requestId.startsWith("elicit_")) return false;
 
@@ -331,7 +331,7 @@ export abstract class McpAgent<
     }
 
     // Check if this is an error response to an elicitation request
-    if (isJSONRPCError(message)) {
+    if (isJSONRPCErrorResponse(message)) {
       const requestId = message.id?.toString();
       if (!requestId || !requestId.startsWith("elicit_")) return false;
 

packages/agents/src/mcp/transport.ts

@@ -2,9 +2,9 @@ import type { Transport } from "@modelcontextprotocol/sdk/shared/transport.js";
 import {
   type MessageExtraInfo,
   type RequestInfo,
-  isJSONRPCError,
+  isJSONRPCErrorResponse,
   isJSONRPCRequest,
-  isJSONRPCResponse,
+  isJSONRPCResultResponse,
   type JSONRPCMessage,
   JSONRPCMessageSchema,
   type RequestId
@@ -326,7 +326,7 @@ export class StreamableHTTPServerTransport implements Transport {
     if (!agent) throw new Error("Agent was not found in send");
 
     let requestId = options?.relatedRequestId;
-    if (isJSONRPCResponse(message) || isJSONRPCError(message)) {
+    if (isJSONRPCResultResponse(message) || isJSONRPCErrorResponse(message)) {
       // If the message is a response, use the request ID from the message
       requestId = message.id;
     }
@@ -336,7 +336,7 @@ export class StreamableHTTPServerTransport implements Transport {
     // Those will be sent via dedicated response SSE streams
     if (requestId === undefined) {
       // For standalone SSE streams, we can only send requests and notifications
-      if (isJSONRPCResponse(message) || isJSONRPCError(message)) {
+      if (isJSONRPCResultResponse(message) || isJSONRPCErrorResponse(message)) {
         throw new Error(
           "Cannot send a response on a standalone SSE stream unless resuming a previous client request"
         );
@@ -385,7 +385,7 @@ export class StreamableHTTPServerTransport implements Transport {
 
     let shouldClose = false;
 
-    if (isJSONRPCResponse(message) || isJSONRPCError(message)) {
+    if (isJSONRPCResultResponse(message) || isJSONRPCErrorResponse(message)) {
       this._requestResponseMap.set(requestId, message);
       const relatedIds = connection.state?.requestIds ?? [];
       // Check if we have responses for all requests using this connection