[Feature] Add screenshot output format option (PNG/JPEG/WebP)

[fuleinist]

Problem: The `browser.screenshot` tool in Playwright MCP outputs PNG by default, but web applications often need JPEG for photos or WebP for optimal compression, requiring post-processing.

Proposed Solution: Extend the screenshot tool to accept an `format` parameter (png/jpeg/webp) so users can specify their desired output format directly without additional conversion steps.

Use Case: When capturing screenshots of dashboards or photo-heavy web apps, users can request JPEG to reduce file size or WebP for modern compression without external tools.

Priority: Nice to have

[masamaru0513]

Hi, I'd like to work on this issue. I'm planning to add a format parameter (png/jpeg/webp) to the screenshot tool in the Playwright monorepo. Please let me know if this is approved for community contribution.

[masamaru0513]

I've done some initial investigation:

• The CDP protocol already supports webp for Page.captureScreenshot, but Playwright's server layer (screenshotter.ts) and public API currently only allow png/jpeg.
• Adding WebP to the MCP tool would also require changes to Playwright core's screenshot API (type definitions, validation, and browser backends).
• The scaleImageToFitMessage function in the MCP layer currently handles png/jpeg decoding/resizing. WebP support here may require a new dependency, which conflicts with the "no new dependencies" policy.

Questions:

1. Should the scope include adding WebP support to Playwright's core screenshot API, or should this be limited to the MCP layer only (e.g., converting from png to webp after capture)?
2. Is there an acceptable approach for WebP resizing without adding new dependencies?