CLS measures visual stability – how much page content shifts during loading. Keep it under 0.1 by specifying image dimensions, avoiding injected content, and using CSS transforms instead of property changes.
What is Cumulative Layout Shift (CLS)?
CLS is one of Google’s Core Web Vitals, designed to quantify visual stability on a page. It tracks instances where content shifts unexpectedly while a page is loading, like text, images, or buttons moving suddenly.
For example, if you’re about to click a button and an ad loads above it, causing the button to move, that counts as a layout shift. Pages with high CLS lead to poor user experience, higher bounce rates, and can lower rankings in search results.
By monitoring and improving CLS, you create a smoother, more predictable browsing experience that benefits both users and SEO performance.
CLS in Different CMS Platforms
WordPress
WordPress sites often face CLS issues from heavy plugins, slow-loading images, or unoptimized themes. Optimizing image sizes, lazy-loading, and using lightweight themes reduces layout shifts.
Shopify
Shopify stores can experience CLS due to dynamic product images, popups, or promotional banners. Implementing proper image dimensions and minimizing third-party scripts helps stabilize layouts.
Wix
Wix users should focus on resizing images, avoiding auto-loaded banners, and checking responsive design to minimize layout shifts.
Webflow
Webflow allows precise control over element positioning and sizing, making it easier to prevent CLS. Consistent spacing, static dimensions, and controlled animations are key.
Custom CMS
Large custom CMS platforms require rigorous testing, CSS optimization, and careful script management to ensure low CLS across all pages, especially high-traffic landing pages.
CLS Across Industries
Ecommerce
High CLS can frustrate shoppers, especially on product pages. Ensuring images, price tags, and call-to-action buttons remain stable improves conversions.
Local Businesses
Even small service websites benefit from low CLS, as unpredictable layout shifts can deter users from contacting or navigating the site.
SaaS
For SaaS platforms, stable dashboards, feature descriptions, and signup forms prevent user frustration and improve onboarding experiences.
Blogs & Publishers
Bloggers need to ensure images, ads, and embedded media don’t move unexpectedly, keeping readers engaged and reducing bounce rates.
Do’s and Don’ts of CLS
Do’s
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Do set explicit width and height for images and videos.
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Do reserve space for ads, banners, and dynamic content.
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Do test pages with tools like Google PageSpeed Insights or Lighthouse.
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Do implement stable fonts and avoid layout shifts during page load.
Don’ts
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Don’t allow content to load asynchronously without reserved space.
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Don’t rely solely on plugins to fix CLS.
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Don’t add popups or banners that appear suddenly.
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Don’t ignore mobile responsiveness CLS issues are often worse on mobile.
Common Mistakes to Avoid
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Failing to define dimensions for images, videos, or embeds.
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Loading third-party scripts late without reserved space.
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Overlooking animations that trigger layout shifts.
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Ignoring mobile optimization for content-heavy pages.
FAQs
What is Cumulative Layout Shift (CLS)?
Cumulative Layout Shift (CLS) is a metric that quantifies unexpected layout shifts during the loading phase of a webpage. It measures the visual stability of a page by calculating how much visible content shifts in the viewport as the page loads.
Why is CLS important for SEO?
CLS is a Core Web Vitals metric used by Google to assess user experience. A high CLS score can lead to poor user experience, which may negatively impact search engine rankings.
What causes high CLS scores?
Common causes include:
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Images or videos without specified dimensions
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Ads, embeds, or iframes without reserved space
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Dynamically injected content
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Web fonts causing invisible text during loading
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Third-party scripts that modify the DOM
What is considered a good CLS score?
A CLS score of 0.1 or less is considered good, indicating minimal unexpected layout shifts. Scores between 0.1 and 0.25 need improvement, and scores above 0.25 are poor and should be addressed.
How can you improve CLS?
To improve CLS:
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Specify width and height for all images and videos
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Reserve space for ads and embeds
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Avoid inserting content above existing content
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Use font-display: swap for web fonts
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Ensure third-party scripts load asynchronously
