PERFORMANCE · SEO GLOSSARY
CLS (Cumulative Layout Shift)
A Core Web Vital that measures unexpected visual shifts in page layout during load. Should be 0.1 or lower.
Definition
Cumulative Layout Shift (CLS) measures how much visible page content unexpectedly moves during the loading phase. A score of 0 means nothing moved. Google's threshold is ≤0.1 for "good", 0.1–0.25 for "needs improvement", and >0.25 for "poor". CLS is part of Core Web Vitals and is a direct Google ranking signal measured from real Chrome user data via CrUX.
Why it matters for SEO
Layout shifts cause users to misclick — you try to tap a button, an ad loads above it, and you accidentally open the wrong link. This is frustrating enough that Google includes it as a ranking factor. The most common causes are images without declared dimensions (browser doesn't reserve space), web fonts that render with different metrics than the fallback font (FOUT causes a shift), and dynamically injected content like banners and cookie notices inserted above existing content.
How DeepSEOAnalysis checks this
The audit checks CLS from CrUX field data for the submitted domain. Field data CLS > 0.1 is flagged as a warning; > 0.25 is critical. Common causes are surfaced from PageSpeed Insights lab data as supplementary recommendations. The most common fix is declaring explicit `width` and `height` on all `<img>` elements so the browser reserves space before the image loads.
Useful tools and resources
GLOSSARY
Related terms
performance
Core Web Vitals
Three Google metrics — LCP, INP, and CLS — that measure real-user loading, interactivity, and visual stability.
Read definition →performance
LCP (Largest Contentful Paint)
The time from page load start until the largest visible content element finishes rendering. Should be under 2.5 seconds.
Read definition →See how your site scores on CLS (Cumulative Layout Shift).
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