fix: allow screenshot capture when filename is an empty string

packages/playwright/src/mcp/browser/tools/screenshot.ts

@@ -23,7 +23,12 @@ import type * as playwright from 'playwright-core';
 
 const screenshotSchema = z.object({
   type: z.enum(['png', 'jpeg']).default('png').describe('Image format for the screenshot. Default is png.'),
-  filename: z.string().optional().describe('File name to save the screenshot to. Defaults to `page-{timestamp}.{png|jpeg}` if not specified.'),
+  filename: z.preprocess(v => {
+    if (v === '')
+      return null;
+
+    return v;
+  }, z.string().nullable()).optional().describe('File name to save the screenshot to. Defaults to `page-{timestamp}.{png|jpeg}` if not specified.'),
   element: z.string().optional().describe('Human-readable element description used to obtain permission to screenshot the element. If not provided, the screenshot will be taken of viewport. If element is provided, ref must be provided too.'),
   ref: z.string().optional().describe('Exact target element reference from the page snapshot. If not provided, the screenshot will be taken of viewport. If ref is provided, element must be provided too.'),
   fullPage: z.boolean().optional().describe('When true, takes a screenshot of the full scrollable page, instead of the currently visible viewport. Cannot be used with element screenshots.'),

tests/mcp/screenshot.spec.ts

@@ -175,6 +175,49 @@ test('browser_take_screenshot (default type should be png)', async ({ startClien
   expect(files[0]).toMatch(/^page-\d{4}-\d{2}-\d{2}T\d{2}-\d{2}-\d{2}-\d{3}Z\.png$/);
 });
 
+test('browser_take_screenshot (filename is empty string)', async ({ startClient, server }, testInfo) => {
+  const outputDir = testInfo.outputPath('output');
+  const { client } = await startClient({
+    config: { outputDir },
+  });
+  expect(await client.callTool({
+    name: 'browser_navigate',
+    arguments: { url: server.HELLO_WORLD },
+  })).toHaveResponse({
+    code: expect.stringContaining(`page.goto('http://localhost`),
+  });
+
+  expect(await client.callTool({
+    name: 'browser_take_screenshot',
+    arguments: {
+      filename: '',
+    },
+  })).toEqual({
+    content: [
+      {
+        text: expect.stringMatching(
+            new RegExp(`page-\\d{4}-\\d{2}-\\d{2}T\\d{2}-\\d{2}-\\d{2}\\-\\d{3}Z\\.png`)
+        ),
+        type: 'text',
+      },
+      {
+        data: expect.any(String),
+        mimeType: 'image/png',
+        type: 'image',
+      },
+    ],
+  });
+
+  const files = [...fs.readdirSync(outputDir)].filter(f => f.endsWith('.png'));
+
+  expect(fs.existsSync(outputDir)).toBeTruthy();
+  expect(files).toHaveLength(1);
+  expect(files[0]).toMatch(
+      new RegExp(`^page-\\d{4}-\\d{2}-\\d{2}T\\d{2}-\\d{2}-\\d{2}-\\d{3}Z\\.png$`)
+  );
+});
+
+
 test('browser_take_screenshot (filename: "output.png")', async ({ startClient, server }, testInfo) => {
   const outputDir = testInfo.outputPath('output');
   const { client } = await startClient({