What Is Cumulative Layout Shift (CLS) and Why It’s Killing Your UX
Cumulative Layout Shift is one of the three Core Web Vitals Google uses to gauge user experience quality. It tracks unexpected shifts in webpage layout during the load phase that aren’t triggered by user interaction. These shifts can cause misclicks and frustration—like when you're about to tap a button and it suddenly moves. CLS is scored from 0 (perfect stability) to 1 (chaotic). A CLS score under 0.1 is considered good, while anything above 0.25 is poor. Common causes of high CLS include images without dimensions, dynamically injected content, and web fonts loading late.
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Use Cases
Sites with low CLS reduce user frustration, leading to smoother journeys—and more purchases.
Google uses CLS to rank pages. A better CLS score = stronger search visibility.
Mobile users feel layout shifts more dramatically. Optimizing CLS gives them a cleaner, touch-friendly experience.
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Frequently Asked Questions
What is a good CLS score?
A good CLS score is 0.1 or less. Scores between 0.1 and 0.25 need improvement, while anything above 0.25 is poor according to Google Web Vitals.
How do I check my site's CLS?
Use tools like Google PageSpeed Insights, Lighthouse in Chrome DevTools, or the Core Web Vitals report in Google Search Console to measure CLS in real-time or historically.
What causes high CLS?
Common culprits include images or videos without width and height attributes, late-loading ads or banners, and dynamically inserted content above existing elements.
Does CLS affect SEO directly?
Set fixed dimensions for images and videos, reserve space for ads and embeds, avoid inserting DOM elements above present content, and preload fonts to prevent late layout shifts.
How can I improve my CLS score?
Absolutely. Mobile responsiveness is critical, and high CLS on mobile can hurt user experience and search performance, especially with Google’s mobile-first indexing.
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