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Cumulative Layout Shift

A Core Web Vital that measures the sum total of all individual layout shift scores for every unexpected layout shift that occurs during the entire lifespan of the page.

AbbreviationCLS
Categoryweb

Overview

CLS measures visual stability. It helps quantify how often users experience unexpected layout shifts—for example, when a button moves just as you're about to click it because an image or ad finished loading above it.

Causes

  • Images without dimensions.
  • Ads, embeds, and iframes without dimensions.
  • Dynamically injected content.
  • Web fonts causing FOIT/FOUT.

Targets

  • Good: Under 0.1.
  • Needs Improvement: Between 0.1 and 0.25.
  • Poor: Over 0.25.

Related Terms

Core Web VitalsSEOLighthouse