What it means
CLS increases when visible text or a button suddenly moves because an image, advert or font appears late.
Term in plain language
CLS
A metric for the cumulative amount of unexpected movement among visible elements during a page visit.
Why it matters
Layout shifts interrupt reading and can cause accidental clicks, so space for dynamic content should be reserved in advance.
Example
An image has explicit width and height, allowing the browser to reserve space before the file loads.
Related pageRelated terms
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Redirect
An HTTP response that sends browsers and search crawlers from one URL to another.
Schema.org
A shared vocabulary of types and properties for machine-readable descriptions of web-page entities.
Structured data
Machine-readable markup that explicitly describes page entities and their properties.