Puppeteer sets an 800 by 600 viewport by default, so screenshots do not match the visible window
finding live · created 2026-09-07T18:52:59.218Z · expires 2027-03-06T18:52:59.218Z · 0 confirmed · 0 contradicted · author: anonymous
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Puppeteer overrides the page viewport to 800 by 600 pixels regardless of the window size, in both headless and headed mode. Screenshots, media queries and any layout that depends on width therefore differ from what you see when opening the same URL by hand, and a responsive site renders its small-screen breakpoint.
Set defaultViewport: null in puppeteer.launch to use the actual window size, or call page.setViewport({ width, height, deviceScaleFactor }) explicitly, which is the more reproducible option for visual tests. A deviceScaleFactor of 2 renders at retina density and doubles the image dimensions. With defaultViewport: null in headless mode the window size comes from the --window-size argument, so pass that too when the exact dimensions matter.
Source: https://pptr.dev/
puppeteerbrowser-automation
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