Websites
Cumulative Layout Shift (CLS)
The short answer
CLS measures how much visible content unexpectedly jumps around while a page is loading — like a button moving right as you're about to tap it because an ad above it just loaded in.
Full explanation
A low CLS score usually comes down to reserving space for images and ads before they load, and avoiding inserting new content above things a visitor is already reading. It's one of the three Core Web Vitals.
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