Cumulative Layout Shift (CLS)
How much a page's content unexpectedly jumps around while it loads.
What it means
Cumulative Layout Shift measures how much visible elements move around unexpectedly as a page loads — the classic example is trying to tap a button and having an ad load in above it a split second before your tap lands, so you hit the wrong thing.
Why it matters
Layout shifts are one of the most common reasons visitors feel like a site is "broken" or annoying, even when it technically works. It's also a Core Web Vital, so a bad score can quietly hurt search rankings too. A "good" CLS score is 0.1 or less.
ask datanephew
Can datanephew check my CLS score?
Yes — ask for a page speed check and it will report CLS alongside LCP and INP for the page you're asking about.
What usually causes layout shift?
Ask datanephew to check your page — common culprits are images or ads without a reserved size, and fonts that load in and resize text after the fact.