A visual regression is an unintended visual change to a webpage — a button moved, text colour changed, a section disappeared, an image broken — caused by a code or content update. Visual regression testing automates the detection of these changes.
A visual monitor captures a screenshot of each tracked page on a schedule (or after every deploy), then pixel-diffs the new image against the previous baseline. Significant differences are flagged for human review with the changed regions highlighted.
Good visual monitoring includes ignore-zones (for ads, timestamps, A/B test variants that legitimately change), responsive variants (desktop + mobile + tablet), and authenticated states (post-login screens).
Many of the worst production bugs are visual — a CSS change that hides the buy button, a CMS edit that removes the pricing section, an A/B test that breaks the navigation. Functional tests miss these. Visual regression catches them within minutes.
See it in the product: Visual monitoring.