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GLOSSARY

What is Cumulative Layout Shift? (CLS)

DEFINITION

Cumulative Layout Shift scores how much visible content moves unexpectedly while a page loads. Web.dev rates 0.1 or less as good and above 0.25 as poor.

Each shift is the impact fraction multiplied by the distance fraction. Images without dimensions, late-loading ads and embeds, and swapping fonts are the usual causes.

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