High Cumulative Layout Shift (CLS)

CLS measures how much visible content moves unexpectedly. Good is 0.1 or less. Most shifts come from images without dimensions, embeds or banners without reserved space, and late font swaps.

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Shifts after loading count too

CLS covers the whole visit, not only initial load, so content inserted later, such as a cookie bar or a promo strip, can fail the metric.

Diagnose it

Symptoms, checks and fixes

Common symptoms

A "CLS issue" in the Core Web Vitals report.
Buttons move just as someone goes to tap them.

Checks to run

Diagnostic checks
Check	How to tell	Fix
Do images and videos have dimensions?	Check img and video tags for width and height, or a CSS aspect-ratio.	Always set width and height so the browser reserves space.[1]
Do embeds, ads or banners push content down?	Watch the page load slowly and note what appears late near the top.	Reserve space with min-height or aspect-ratio, or place late content lower on the page.[1]
Do fonts cause a jump?	See whether text reflows when the web font replaces the fallback.	Preload critical fonts and use font-display: optional or matched fallback metrics.[1]
Do animations move layout?	Look for animated top, left or size properties.	Animate transform instead.[1]