Performance

CLS Checker

Cumulative Layout Shift measures how much the page visually jumps around as it loads — late-loading ads, web fonts, and images without dimensions are the usual culprits. Google's target is under 0.1.

Uses Google PageSpeed Insights — typically 10–30 seconds. Results are lab data; real-user numbers may differ.

What is a CLS checker?

A CLS checker measures Cumulative Layout Shift — how much content unexpectedly moves while the page loads. This free CLS test runs Google PageSpeed Insights so you can check CLS on any URL.

Diagnose & fix layout shifts

The most common causes of a high cumulative layout shift are images and embeds without dimensions, ads/banners with no reserved space, and late web-font swaps. Set explicit sizes (or aspect-ratio), reserve space, and preload fonts, then re-test.

What's a good CLS?

Aim for 0.1 or less. 0.1–0.25 needs improvement; above 0.25 is poor. CLS is a Core Web Vital, so reducing it helps users and rankings.

More Core Web Vitals tools

Check the rest: LCP Checker, INP Checker, TTFB Checker, and the full Page Speed Test.

Frequently asked questions

A CLS checker measures Cumulative Layout Shift — how much the page unexpectedly jumps around as it loads. This free CLS test runs Google PageSpeed Insights on any URL and reports your CLS score so you can check visual stability.
Google considers CLS good at 0.1 or less, needs-improvement up to 0.25, and poor above 0.25. Lower is better — aim for under 0.1.
Always set width and height (or aspect-ratio) on images and embeds, reserve space for ads and banners, preload web fonts to avoid swap, and never insert content above existing content. These eliminate most layout shifts.
Completely free and online, with no account required. It's part of WebsiteAuditTools' free suite of Core Web Vitals tools.