Performance

CLS (Cumulative Layout Shift)

A Core Web Vital metric that measures the visual stability of a page.

Cumulative Layout Shift (CLS) measures how much the content on your page moves around as it loads. Have you ever gone to click a button, but suddenly an ad loads and pushes the button down, causing you to click the wrong thing? That is a layout shift.

Why It Matters

  • User Frustration: It is one of the most annoying user experiences.
  • SEO Penalty: Google penalizes sites with high CLS scores.

Common Causes

  • Images without dimensions (width/height attributes).
  • Ads, embeds, and iframes without reserved space.
  • Web fonts causing “Flash of Invisible Text” (FOIT).
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Related Concepts

Performance

Core Web Vitals (CWV)

A set of specific factors that Google considers important in a webpage's overall user experience.

Performance

LCP (Largest Contentful Paint)

A Core Web Vital that measures when the largest content element on a page becomes visible. Learn what causes slow LCP and how to fix it.

Performance

Bounce Rate

The percentage of visitors to a particular website who navigate away from the site after viewing only one page.

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