feat(screenshot): add webp output format

Adds `webp` to the screenshot type union for `page.screenshot()`,
`locator.screenshot()`, the MCP `browser_take_screenshot` tool, and
the playwright-cli `screenshot` command. Encoded natively by each
browser — CDP for Chromium, `Page.screenshot` for Firefox, and
`Page.snapshotRect` (with format + quality) for WebKit; the WebKit
path also drops the PNG→JPEG re-encode round-trip in Node.

The MCP/CLI tools infer the format from the filename extension when
`type` is unset. The CLI help generator now lists enum choices for
any `z.enum` option.

WebP screenshots are not supported in WebKit on macOS because
CoreGraphics does not ship a webp encoder UTI; the WebKit delegate
throws a clear error there.

Fixes microsoft/playwright-mcp#1632

Author: yury-s

docs/src/api/params.md

@@ -1287,7 +1287,7 @@ relative path, then it is resolved relative to the current working directory. If
 saved to the disk.
 
 ## screenshot-option-type
-- `type` <[ScreenshotType]<"png"|"jpeg">>
+- `type` <[ScreenshotType]<"png"|"jpeg"|"webp">>
 
 Specify screenshot type, defaults to `png`.
 

packages/playwright-client/types/types.d.ts

@@ -12313,7 +12313,7 @@ export interface ElementHandle<T=Node> extends JSHandle<T> {
     /**
      * Specify screenshot type, defaults to `png`.
      */
-    type?: "png"|"jpeg";
+    type?: "png"|"jpeg"|"webp";
   }): Promise<Buffer>;
 
   /**
@@ -24124,7 +24124,7 @@ export interface LocatorScreenshotOptions {
   /**
    * Specify screenshot type, defaults to `png`.
    */
-  type?: "png"|"jpeg";
+  type?: "png"|"jpeg"|"webp";
 }
 
 interface ElementHandleWaitForSelectorOptions {
@@ -24797,7 +24797,7 @@ export interface PageScreenshotOptions {
   /**
    * Specify screenshot type, defaults to `png`.
    */
-  type?: "png"|"jpeg";
+  type?: "png"|"jpeg"|"webp";
 }
 
 type Devices = {

packages/playwright-core/src/client/elementHandle.ts

@@ -317,13 +317,15 @@ export async function convertInputFiles(platform: Platform, files: string | File
   return { payloads };
 }
 
-export function determineScreenshotType(options: { path?: string, type?: 'png' | 'jpeg' }): 'png' | 'jpeg' | undefined {
+export function determineScreenshotType(options: { path?: string, type?: 'png' | 'jpeg' | 'webp' }): 'png' | 'jpeg' | 'webp' | undefined {
   if (options.path) {
     const mimeType = getMimeTypeForPath(options.path);
     if (mimeType === 'image/png')
       return 'png';
     else if (mimeType === 'image/jpeg')
       return 'jpeg';
+    else if (mimeType === 'image/webp')
+      return 'webp';
     throw new Error(`path: unsupported mime type "${mimeType}"`);
   }
   return options.type;

packages/playwright-core/src/protocol/validator.ts

@@ -1872,7 +1872,7 @@ scheme.ElementHandleQuerySelectorAllResult = tObject({
 });
 scheme.ElementHandleScreenshotParams = tObject({
   timeout: tFloat,
-  type: tOptional(tEnum(['png', 'jpeg'])),
+  type: tOptional(tEnum(['png', 'jpeg', 'webp'])),
   quality: tOptional(tInt),
   omitBackground: tOptional(tBoolean),
   caret: tOptional(tEnum(['hide', 'initial'])),
@@ -2430,7 +2430,7 @@ scheme.PageExpectScreenshotResult = tObject({
 });
 scheme.PageScreenshotParams = tObject({
   timeout: tFloat,
-  type: tOptional(tEnum(['png', 'jpeg'])),
+  type: tOptional(tEnum(['png', 'jpeg', 'webp'])),
   quality: tOptional(tInt),
   fullPage: tOptional(tBoolean),
   clip: tOptional(tType('Rect')),

packages/playwright-core/src/server/bidi/bidiPage.ts

@@ -479,6 +479,8 @@ export class BidiPage implements PageDelegate {
   }
 
   async takeScreenshot(progress: Progress, format: string, documentRect: types.Rect | undefined, viewportRect: types.Rect | undefined, quality: number | undefined, fitsViewport: boolean, scale: 'css' | 'device'): Promise<Buffer> {
+    if (format === 'webp')
+      throw new Error('webp screenshots are not supported via WebDriver BiDi');
     const rect = (documentRect || viewportRect)!;
     const { data } = await progress.race(this._session.send('browsingContext.captureScreenshot', {
       context: this._session.sessionId,

packages/playwright-core/src/server/chromium/crPage.ts

@@ -247,7 +247,7 @@ export class CRPage implements PageDelegate {
     await this._mainFrameSession._client.send('Emulation.setDefaultBackgroundColorOverride', { color });
   }
 
-  async takeScreenshot(progress: Progress, format: 'png' | 'jpeg', documentRect: types.Rect | undefined, viewportRect: types.Rect | undefined, quality: number | undefined, fitsViewport: boolean, scale: 'css' | 'device'): Promise<Buffer> {
+  async takeScreenshot(progress: Progress, format: 'png' | 'jpeg' | 'webp', documentRect: types.Rect | undefined, viewportRect: types.Rect | undefined, quality: number | undefined, fitsViewport: boolean, scale: 'css' | 'device'): Promise<Buffer> {
     const { visualViewport, contentSize, cssContentSize } = await progress.race(this._mainFrameSession._client.send('Page.getLayoutMetrics'));
     if (!documentRect) {
       documentRect = {

packages/playwright-core/src/server/firefox/ffPage.ts

@@ -455,7 +455,7 @@ export class FFPage implements PageDelegate {
       throw new Error('Not implemented');
   }
 
-  async takeScreenshot(progress: Progress, format: 'png' | 'jpeg', documentRect: types.Rect | undefined, viewportRect: types.Rect | undefined, quality: number | undefined, fitsViewport: boolean, scale: 'css' | 'device'): Promise<Buffer> {
+  async takeScreenshot(progress: Progress, format: 'png' | 'jpeg' | 'webp', documentRect: types.Rect | undefined, viewportRect: types.Rect | undefined, quality: number | undefined, fitsViewport: boolean, scale: 'css' | 'device'): Promise<Buffer> {
     if (!documentRect) {
       const scrollOffset = await this._page.mainFrame().waitForFunctionValueInUtility(progress, () => ({ x: window.scrollX, y: window.scrollY }));
       documentRect = {
@@ -466,7 +466,7 @@ export class FFPage implements PageDelegate {
       };
     }
     const { data } = await progress.race(this._session.send('Page.screenshot', {
-      mimeType: ('image/' + format) as ('image/png' | 'image/jpeg'),
+      mimeType: ('image/' + format) as ('image/png' | 'image/jpeg' | 'image/webp'),
       clip: documentRect,
       quality,
       omitDeviceScaleFactor: scale === 'css',

packages/playwright-core/src/server/screenshotter.ts

@@ -35,7 +35,7 @@ declare global {
 }
 
 export type ScreenshotOptions = {
-  type?: 'png' | 'jpeg';
+  type?: 'png' | 'jpeg' | 'webp';
   quality?: number;
   omitBackground?: boolean;
   animations?: 'disabled' | 'allow';
@@ -297,7 +297,7 @@ export class Screenshotter {
     }
   }
 
-  private async _screenshot(progress: Progress, format: 'png' | 'jpeg', documentRect: types.Rect | undefined, viewportRect: types.Rect | undefined, fitsViewport: boolean, options: ScreenshotOptions): Promise<Buffer> {
+  private async _screenshot(progress: Progress, format: 'png' | 'jpeg' | 'webp', documentRect: types.Rect | undefined, viewportRect: types.Rect | undefined, fitsViewport: boolean, options: ScreenshotOptions): Promise<Buffer> {
     if ((options as any).__testHookBeforeScreenshot)
       await progress.race((options as any).__testHookBeforeScreenshot());
 
@@ -307,7 +307,7 @@ export class Screenshotter {
     const cleanupHighlight = await this._maskElements(progress, options);
 
     try {
-      const quality = format === 'jpeg' ? options.quality ?? 80 : undefined;
+      const quality = format === 'jpeg' ? options.quality ?? 80 : format === 'webp' ? options.quality : undefined;
       const buffer = await this._page.delegate.takeScreenshot(progress, format, documentRect, viewportRect, quality, fitsViewport, options.scale || 'device');
       await progress.race(cleanupHighlight());
       if (shouldSetDefaultBackground)
@@ -353,20 +353,20 @@ function trimClipToSize(clip: types.Rect, size: types.Size): types.Rect {
   return result;
 }
 
-export function validateScreenshotOptions(options: ScreenshotOptions): 'png' | 'jpeg' {
-  let format: 'png' | 'jpeg' | null = null;
+export function validateScreenshotOptions(options: ScreenshotOptions): 'png' | 'jpeg' | 'webp' {
+  let format: 'png' | 'jpeg' | 'webp' | null = null;
   // options.type takes precedence over inferring the type from options.path
   // because it may be a 0-length file with no extension created beforehand (i.e. as a temp file).
   if (options.type) {
-    assert(options.type === 'png' || options.type === 'jpeg', 'Unknown options.type value: ' + options.type);
+    assert(options.type === 'png' || options.type === 'jpeg' || options.type === 'webp', 'Unknown options.type value: ' + options.type);
     format = options.type;
   }
 
   if (!format)
     format = 'png';
 
   if (options.quality !== undefined) {
-    assert(format === 'jpeg', 'options.quality is unsupported for the ' + format + ' screenshots');
+    assert(format !== 'png', 'options.quality is unsupported for the ' + format + ' screenshots');
     assert(typeof options.quality === 'number', 'Expected options.quality to be a number but found ' + (typeof options.quality));
     assert(Number.isInteger(options.quality), 'Expected options.quality to be an integer');
     assert(options.quality >= 0 && options.quality <= 100, 'Expected options.quality to be between 0 and 100 (inclusive), got ' + options.quality);

packages/playwright-core/src/server/webkit/wkPage.ts

@@ -15,8 +15,6 @@
  * limitations under the License.
  */
 
-import { PNG } from 'pngjs';
-import jpegjs from 'jpeg-js';
 import { headersArrayToObject, headersObjectToArray } from '@isomorphic/headers';
 import { splitErrorMessage } from '@isomorphic/stackTrace';
 import { eventsHelper } from '@utils/eventsHelper';
@@ -870,16 +868,15 @@ export class WKPage implements PageDelegate {
   }
 
   async takeScreenshot(progress: Progress, format: string, documentRect: types.Rect | undefined, viewportRect: types.Rect | undefined, quality: number | undefined, fitsViewport: boolean, scale: 'css' | 'device'): Promise<Buffer> {
+    if (format === 'webp' && process.platform === 'darwin')
+      throw new Error('webp screenshots are not supported in WebKit on macOS');
     const rect = (documentRect || viewportRect)!;
     const omitDeviceScaleFactor = scale === 'css';
     this.validateScreenshotDimension(rect.width, omitDeviceScaleFactor);
     this.validateScreenshotDimension(rect.height, omitDeviceScaleFactor);
-    const result = await progress.race(this._session.send('Page.snapshotRect', { ...rect, coordinateSystem: documentRect ? 'Page' : 'Viewport', omitDeviceScaleFactor }));
-    const prefix = 'data:image/png;base64,';
-    let buffer: Buffer = Buffer.from(result.dataURL.substr(prefix.length), 'base64');
-    if (format === 'jpeg')
-      buffer = jpegjs.encode(PNG.sync.read(buffer), quality).data;
-    return buffer;
+    const result = await progress.race(this._session.send('Page.snapshotRect', { ...rect, coordinateSystem: documentRect ? 'Page' : 'Viewport', omitDeviceScaleFactor, format: format as 'png' | 'jpeg' | 'webp', quality }));
+    // Strip 'data:image/png;base64,' prefix.
+    return Buffer.from(result.dataURL.substring(result.dataURL.indexOf(',') + 1), 'base64');
   }
 
   async getContentFrame(handle: dom.ElementHandle): Promise<frames.Frame | null> {

packages/playwright-core/src/tools/backend/response.ts

@@ -58,7 +58,7 @@ export class Response {
   readonly toolName: string;
   readonly toolArgs: Record<string, any>;
   private _clientWorkspace: string;
-  private _imageResults: { data: Buffer, imageType: 'png' | 'jpeg' }[] = [];
+  private _imageResults: { data: Buffer, imageType: 'png' | 'jpeg' | 'webp' }[] = [];
   private _raw: boolean;
   private _json: boolean;
   private _writtenFiles = new Set<string>();
@@ -127,7 +127,7 @@ export class Response {
     this.addTextResult(`- [${title}](${relativeName})`);
   }
 
-  async registerImageResult(data: Buffer, imageType: 'png' | 'jpeg') {
+  async registerImageResult(data: Buffer, imageType: 'png' | 'jpeg' | 'webp') {
     this._imageResults.push({ data, imageType });
   }
 
@@ -219,7 +219,7 @@ export class Response {
     if (this._context.config.imageResponses !== 'omit') {
       for (const imageResult of this._imageResults) {
         const scaledData = scaleImageToFitMessage(imageResult.data, imageResult.imageType);
-        content.push({ type: 'image', data: scaledData.toString('base64'), mimeType: imageResult.imageType === 'png' ? 'image/png' : 'image/jpeg' });
+        content.push({ type: 'image', data: scaledData.toString('base64'), mimeType: `image/${imageResult.imageType}` });
       }
     }