Cumulative Layout Shift (CLS)
Cumulative Layout Shift measures how much a page's content unexpectedly moves around as it loads, a Core Web Vital capturing visual stability.
Also known as: CLS
CLS measures how much the page jumps around while loading. A Core Web Vitals metric, it scores unexpected layout shifts — text that reflows when a late image loads, a button that moves just as you tap it — with a lower score meaning a more stable, predictable page.
CLS is the most user-experience-focused of the vitals and the least directly tied to AEO, but it still belongs to the access pillar's quality bar: a stable, well-built page signals technical care, and the fixes (reserving space for images and embeds, avoiding content injected above existing content) are cheap and improve the experience for everyone. It rounds out LCP and FCP as part of an overall fast, solid page.
Example. Reserving explicit dimensions for images so the text doesn't jump when they load keeps CLS low — a small discipline that makes the page feel stable and professional as it renders.
Relevant pillar
Related terms
- Core Web VitalsCore Web Vitals are Google's set of user-experience metrics for loading, interactivity, and visual stability, a measurable proxy for the page speed and quality that support AI visibility.
- Largest Contentful Paint (LCP)Largest Contentful Paint measures how long it takes for the biggest piece of content to render, a Core Web Vital that captures how quickly a page feels loaded.
- First Contentful Paint (FCP)First Contentful Paint is a performance metric measuring how long after navigation the browser renders the first piece of page content, used as a proxy for how quickly a page becomes useful.