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
Core Web Vitals (CWV)
A set of specific factors that Google considers important in a webpage's overall user experience.
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.
Bounce Rate
The percentage of visitors to a particular website who navigate away from the site after viewing only one page.