Functional tests confirm a button works. They don't notice it moved four pixels, lost its hover state, or disappeared behind a banner on one browser. PixellPeep catches those visual breaks before customers see them. Upload the screenshots you already capture or let PixellPeep capture URLs, and one CI manifest turns dozens of screens into a single pull-request check. Six comparison algorithms, from pixel-exact to perceptual, so you set strictness per screen. Live since June 2026.