Cumulative Layout Shift within Core Web Vitals threshold

Questions about this rule

Does PERF_CLS affect my score?

Yes. It is an importance 6 rule at SPECIFICATION confidence, so a failure costs 6 × 1 points of impact in the Performance category before that category is normalised to 100.

What does SPECIFICATION confidence mean?

A standard says so: HTML, WCAG, an RFC or Google's own documentation. Confidence is a declared tier rather than a per-rule number, so every rule backed by the same class of evidence carries the same weight - which is what makes the score reproducible instead of hand-tuned.

How do I check PERF_CLS on my own site?

Paste your URL into the box above and it runs only this rule, usually in a couple of seconds. It is also included in the Performance checker and in a full scan.