diff --git a/packages/playwright-core/src/tools/backend/response.ts b/packages/playwright-core/src/tools/backend/response.ts
index 6d6593303bdc3..f0b9266869ba8 100644
--- a/packages/playwright-core/src/tools/backend/response.ts
+++ b/packages/playwright-core/src/tools/backend/response.ts
@@ -151,7 +151,7 @@ export class Response {
     const content: (TextContent | ImageContent)[] = [
       {
         type: 'text',
-        text: redactText(text.join('\n')),
+        text: sanitizeUnicode(redactText(text.join('\n'))),
       }
     ];
 
@@ -265,6 +265,14 @@ function trimMiddle(text: string, maxLength: number) {
   return text.slice(0, Math.floor(maxLength / 2)) + '...' + text.slice(- 3 - Math.floor(maxLength / 2));
 }
 
+/**
+ * Sanitizes a string to ensure it only contains well-formed Unicode.
+ * Replaces lone surrogates with U+FFFD using String.prototype.toWellFormed().
+ */
+function sanitizeUnicode(text: string): string {
+  return text.toWellFormed();
+}
+
 function parseSections(text: string): Map<string, string> {
   const sections = new Map<string, string>();
   const sectionHeaders = text.split(/^### /m).slice(1); // Remove empty first element
diff --git a/tests/mcp/unicode-serialization.spec.ts b/tests/mcp/unicode-serialization.spec.ts
new file mode 100644
index 0000000000000..f5bf825a47294
--- /dev/null
+++ b/tests/mcp/unicode-serialization.spec.ts
@@ -0,0 +1,56 @@
+/**
+ * Copyright (c) Microsoft Corporation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { test, expect } from './fixtures';
+
+test.describe('unicode serialization', () => {
+  test.use({ mcpArgs: ['--no-sandbox'] });
+
+  test('handles lone surrogates in page content', async ({ client, server }) => {
+    server.setContent('/', `Text with ${String.fromCharCode(0xD800)} lone surrogate`, 'text/html');
+
+    const result = await client.callTool({
+      name: 'browser_navigate',
+      arguments: { url: server.PREFIX },
+    });
+
+    expect(result.content[0].text).toContain('Page URL:');
+  });
+
+  test('preserves valid emoji and surrogate pairs', async ({ client, server }) => {
+    server.setContent('/', 'Valid emoji: 💀 skull and text', 'text/html');
+
+    const result = await client.callTool({
+      name: 'browser_navigate',
+      arguments: { url: server.PREFIX },
+    });
+
+    expect(result.content[0].text).toContain('emoji');
+  });
+
+  test('handles console messages with lone surrogates', async ({ startClient, server }) => {
+    server.setContent('/', `<script>console.log('msg ${String.fromCharCode(0xD800)} surrog')</script>`, 'text/html');
+
+    const { client } = await startClient({ args: ['--console-level=debug'] });
+
+    const result = await client.callTool({
+      name: 'browser_navigate',
+      arguments: { url: server.PREFIX },
+    });
+
+    expect(result.content[0].text).toBeDefined();
+  });
+});