What Is CLS?
Cumulative Layout Shift (CLS) quantifies how much visible content shifts unexpectedly as a page loads. It measures the sum of all individual layout shift scores throughout the page's lifecycle. A good CLS score is under 0.1; poor is over 0.25. Layout shifts are caused by images without dimensions, dynamically injected content, web fonts, and ads loading above the fold.
Why CLS Matters
Layout shifts frustrate users — clicking a button only to have the page jump and accidentally clicking something else is a terrible experience. CLS is a Core Web Vital and a Google ranking factor. Pages with high CLS provide poor user experiences and may rank lower.
How to Improve CLS
Always set width and height attributes on images and videos. Reserve space for ads and dynamic content with CSS. Use font-display: swap for web fonts. Avoid inserting content above existing content after page load. Test with Chrome DevTools Performance panel.
📖 Related Article: Core Web Vitals Guide — Read our in-depth guide for practical examples and advanced techniques.
Professional SEO & DevOps Tools
Analyze server logs and crawl websites with GetBeast's professional desktop tools.