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Mockup
How far off the design is this build?
Holding a screenshot up next to a build finds nothing smaller than about eight pixels. Putting the comp *over* the page finds everything, provided the difference is computed rather than approximated: this draws the comp inverted at exactly fifty per cent and computes the difference, because `mix-blend-mode` gives a picture that looks like a diff and is not one.
Reach itPress ⌘+K on any tab and type mockup.Ctrl+Kon Windows and Linux
TWO BUILDS9 browsers
Chromelisting in reviewFirefoxlisting in reviewBravelisting in reviewOperalisting in reviewEdgelisting in review4 moreChromium browsers: Arc, Vivaldi, Chromium, Opera GXthe Chrome buildin the panel · free, no counter
What this actually is
pin a mockup over the page and diff it by pixelAt handover, and any time a designer and a developer disagree about whether something shipped as drawn. Position the comp once against a known corner and the rest of the page lines up with it.
Asked about this tool
4 of themWhy not use mix-blend-mode: difference?
Because it blends against whatever is behind the layer, including our own chrome, and the result changes with the page’s own stacking. Drawing inverted at exactly 50% and computing the difference gives a picture that means one thing.
Does my comp get uploaded anywhere?
No. It is read in your browser into a data URL and handed to the page in a message. It is never stored and never sent, which is also why there is a size ceiling.
The comp drifts as I scroll. Why?
It is positioned against the document rather than the viewport, which is what you want for a full-page mockup. If it drifts relative to the content, the page’s own scroll container is not the document - the Scrolling diagnostic will name it.
Can I overlay a second comp?
One at a time. Two comps and a page is three layers with no honest way to say which difference belongs to which, and the answer people actually want is a diff against one reference.
TWO BUILDS9 browsers
Chromelisting in reviewFirefoxlisting in reviewBravelisting in reviewOperalisting in reviewEdgelisting in review4 moreChromium browsers: Arc, Vivaldi, Chromium, Opera GXthe Chrome build63 of these · no host permissions · three free audits