Page speed
Cumulative Layout Shift
CLS under 0.1; critical over 0.25
What we check
CLS under 0.1; critical over 0.25
Why it matters
Content jumping while it loads makes people tap the wrong thing.
How to fix it
Set width and height on images and reserve space for late content.
How it affects your score
This check sits in Page speed, which is worth 20% of the overall score. A critical result costs the full weight of the check; a warning costs half. If we can't measure it on your page, we leave it out of the score entirely.