What is Cumulative Layout Shift?
CLS: the Core Web Vital that measures visual stability. It quantifies how much visible content unexpectedly shifts during the page's lifetime. A good CLS score is 0.1 or less, meaning elements stay where you expect them as the page loads and renders.
My perspective
In practice
The most common culprits: images and ads without explicit dimensions, dynamically injected content above the fold, and web fonts that cause text to reflow (FOUT/FOIT). Fixes are usually straightforward: set width/height or aspect-ratio on media, reserve space for dynamic elements, and use font-display: optional or preloaded self-hosted fonts. CLS improvements are among the most noticeable UX wins.