[MCP] WebP screenshot above 16383 px returns an empty image

[SixFive7]

browser_take_screenshot with type webp and fullPage on a document taller than 16383 px returns an empty image and writes a zero-byte file, with no error. 16383 px works, 16384 px does not. png and jpeg are fine at the same heights.

This looks like the WebP dimension limit surfacing as success. An error, or a fallback to png above the limit, would make the result honest.

Seen with @playwright/mcp 0.0.80, playwright-core 1.63.0-alpha-2026-08-31, Chromium 153.0.8010.12, Windows 11.

[mohanram-dev]

Opened PR #42721 to address this issue by validating WebP's 16,383px specification limit across render scales and guarding against silent 0-byte screenshot buffers.

[dcrousso]

working on an upstream fix for this https://chromium-review.googlesource.com/c/chromium/src/+/8416650

[bickov]

16383 is libwebp's hard cap on both width and height (WEBP_MAX_DIMENSION), it's baked into the bitstream header, not something Chromium or Playwright can raise. So the boundary you found is exactly right and not a coincidence.

The actual bug is probably in how the encode call's return value gets handled. If libwebp refuses to encode above that size, playwright-core should be seeing a failed encode, not a successful call with an empty buffer. Worth checking whether the wrapper checks the encoder's return code before writing bytes to disk, versus assuming success whenever the call returns without throwing.

[alok-108]

Hi Devin Rousso (@dcrousso),

I saw your upstream Chromium patch (CL 8416650) which will make CDP report Unable to encode screenshot on encoding failures in upcoming Chromium releases.

In the meantime, on current Chromium releases, WebP encoding failures return { data: '' }, which causes crPage.ts to return an empty buffer and @playwright/mcp's browser_take_screenshot to silently write 0-byte .webp files to disk without raising an error.

Rather than hardcoding format/dimension limits in Playwright (which was rightly avoided in #42721), I have a clean, non-intrusive fix ready that:

1. In crPage.ts: throws Unable to encode screenshot if !result.data, aligning Playwright immediately with your upstream Chromium fix.
2. In @playwright/mcp (screenshot.ts): guards against writing a 0-byte file if !data.length.
3. Includes unit & MCP regression tests without any dimension hardcoding.

Would you be open to a PR for this targeted fix, or would you prefer waiting exclusively for the Chromium roll in v1.64? Happy to submit the PR if this aligns with the team's preference.