diff --git a/packages/playwright-core/src/tools/mcp/index.ts b/packages/playwright-core/src/tools/mcp/index.ts
index 51619e006708a..a1a1c8c4b5a0c 100644
--- a/packages/playwright-core/src/tools/mcp/index.ts
+++ b/packages/playwright-core/src/tools/mcp/index.ts
@@ -43,7 +43,7 @@ export async function createConnection(userConfig: Config = {}, contextGetter?:
     },
     disposed: async () => { }
   };
-  return createServer('api', packageJSON.version, backendFactory, false);
+  return createServer('api', packageJSON.version, backendFactory, Promise.resolve(), false);
 }
 
 class SimpleBrowser {
diff --git a/packages/playwright-core/src/tools/utils/mcp/DEPS.list b/packages/playwright-core/src/tools/utils/mcp/DEPS.list
index f5833b09a35c3..b050876e51b50 100644
--- a/packages/playwright-core/src/tools/utils/mcp/DEPS.list
+++ b/packages/playwright-core/src/tools/utils/mcp/DEPS.list
@@ -1,5 +1,6 @@
 [*]
 @utils/**
+@isomorphic/**
 node_modules/@modelcontextprotocol/sdk/server/index.js
 node_modules/@modelcontextprotocol/sdk/server/sse.js
 node_modules/@modelcontextprotocol/sdk/server/stdio.js
diff --git a/packages/playwright-core/src/tools/utils/mcp/http.ts b/packages/playwright-core/src/tools/utils/mcp/http.ts
index 8d6a2fb38dd5f..4f81786960b3f 100644
--- a/packages/playwright-core/src/tools/utils/mcp/http.ts
+++ b/packages/playwright-core/src/tools/utils/mcp/http.ts
@@ -24,6 +24,7 @@ import { SSEServerTransport } from '@modelcontextprotocol/sdk/server/sse.js';
 import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
 import { urlHostFromAddress } from '@utils/httpServer';
 import { createHttpServer, startHttpServer } from '@utils/network';
+import { ManualPromise } from '@isomorphic/manualPromise';
 
 import * as mcpServer from './server';
 
@@ -123,7 +124,7 @@ async function handleSSE(serverBackendFactory: ServerBackendFactory, req: http.I
     const transport = new SSEServerTransport('/sse', res);
     sessions.set(transport.sessionId, transport);
     testDebug(`create SSE session`);
-    await mcpServer.connect(serverBackendFactory, transport, false);
+    await mcpServer.connect(serverBackendFactory, transport, Promise.resolve(), false);
     res.on('close', () => {
       testDebug(`delete SSE session`);
       sessions.delete(transport.sessionId);
@@ -135,16 +136,22 @@ async function handleSSE(serverBackendFactory: ServerBackendFactory, req: http.I
   res.end('Method not allowed');
 }
 
-async function handleStreamable(serverBackendFactory: ServerBackendFactory, req: http.IncomingMessage, res: http.ServerResponse, sessions: Map<string, StreamableHTTPServerTransportType>) {
+async function handleStreamable(serverBackendFactory: ServerBackendFactory, req: http.IncomingMessage, res: http.ServerResponse, sessions: Map<string, { transport: StreamableHTTPServerTransportType, transportInitialized: ManualPromise<void> }>) {
   const sessionId = req.headers['mcp-session-id'] as string | undefined;
   if (sessionId) {
-    const transport = sessions.get(sessionId);
-    if (!transport) {
+    const sessionInfo = sessions.get(sessionId);
+    if (!sessionInfo) {
       res.statusCode = 404;
       res.end('Session not found');
       return;
     }
-    return await transport.handleRequest(req, res);
+    if (req.method === 'GET') {
+      // As per spec, GET is for the event stream only, when we see it consider transport bidirectionally ready.
+      const streamResponse = sessionInfo.transport.handleRequest(req, res);
+      sessionInfo.transportInitialized.resolve();
+      return streamResponse;
+    }
+    return sessionInfo.transport.handleRequest(req, res);
   }
 
   if (req.method === 'POST') {
@@ -152,8 +159,11 @@ async function handleStreamable(serverBackendFactory: ServerBackendFactory, req:
       sessionIdGenerator: () => crypto.randomUUID(),
       onsessioninitialized: async sessionId => {
         testDebug(`create http session`);
-        await mcpServer.connect(serverBackendFactory, transport, true);
-        sessions.set(sessionId, transport);
+        const sessionInfo = { transport, transportInitialized: new ManualPromise() };
+        // Only give the client 5 seconds to reach for the event stream.
+        setTimeout(() => sessionInfo.transportInitialized.resolve(), 5000);
+        sessions.set(sessionId, sessionInfo);
+        await mcpServer.connect(serverBackendFactory, sessionInfo.transport, sessionInfo.transportInitialized, true);
       }
     });
 
diff --git a/packages/playwright-core/src/tools/utils/mcp/server.ts b/packages/playwright-core/src/tools/utils/mcp/server.ts
index 4bd2ea7eef76f..15cf6ebe1b5ed 100644
--- a/packages/playwright-core/src/tools/utils/mcp/server.ts
+++ b/packages/playwright-core/src/tools/utils/mcp/server.ts
@@ -75,12 +75,12 @@ export type ServerBackendFactory = {
   disposed: (backend: ServerBackend) => Promise<void>;
 };
 
-export async function connect(factory: ServerBackendFactory, transport: Transport, runHeartbeat: boolean) {
-  const server = createServer(factory.name, factory.version, factory, runHeartbeat);
+export async function connect(factory: ServerBackendFactory, transport: Transport, transportInitialized: Promise<void>, runHeartbeat: boolean) {
+  const server = createServer(factory.name, factory.version, factory, transportInitialized, runHeartbeat);
   await server.connect(transport);
 }
 
-export function createServer(name: string, version: string, factory: ServerBackendFactory, runHeartbeat: boolean): ServerType {
+export function createServer(name: string, version: string, factory: ServerBackendFactory, transportInitialized: Promise<void>, runHeartbeat: boolean): ServerType {
   const server = new Server({ name, version }, {
     capabilities: {
       tools: {},
@@ -102,7 +102,7 @@ export function createServer(name: string, version: string, factory: ServerBacke
 
     try {
       if (!backendPromise) {
-        backendPromise = initializeServer(server, factory, runHeartbeat).catch(e => {
+        backendPromise = initializeServer(server, factory, transportInitialized, runHeartbeat).catch(e => {
           backendPromise = undefined;
           throw e;
         });
@@ -129,10 +129,11 @@ export function createServer(name: string, version: string, factory: ServerBacke
   return server;
 }
 
-const initializeServer = async (server: ServerType, factory: ServerBackendFactory, runHeartbeat: boolean): Promise<ServerBackend> => {
+const initializeServer = async (server: ServerType, factory: ServerBackendFactory, transportInitialized: Promise<void>, runHeartbeat: boolean): Promise<ServerBackend> => {
   const capabilities = server.getClientCapabilities();
   let clientRoots: Root[] = [];
   if (capabilities?.roots) {
+    await transportInitialized;
     const { roots } = await server.listRoots().catch(e => {
       serverDebug(e);
       return { roots: [] };
@@ -196,7 +197,7 @@ export async function start(serverBackendFactory: ServerBackendFactory, options:
     // The SDK's StdioServerTransport doesn't detect peer disconnect — it never listens for stdin
     // end-of-stream. Wire it up so callTool requests can be cancelled when the client goes away.
     process.stdin.on('end', () => void transport.close());
-    await connect(serverBackendFactory, transport, false);
+    await connect(serverBackendFactory, transport, Promise.resolve(), false);
     return;
   }