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When optimizing a website for better user experience and search engine rankings, one important metric to consider is Cumulative Layout Shift (CLS). A high CLS score indicates that elements on your page shift unexpectedly, which can frustrate users. Understanding the common causes of high CLS scores can help you implement effective solutions.
What Is CLS and Why Is It Important?
CLS measures the visual stability of a webpage. It quantifies how much content moves around as the page loads. A low CLS score results in a stable experience, while a high score can lead to accidental clicks and a poor user experience. Search engines like Google prioritize pages with low CLS scores in their rankings.
Common Causes of High CLS Scores
1. Images Without Dimensions
When images do not have specified width and height attributes, the browser cannot allocate space before the image loads. This causes content to shift once the image appears. Always include explicit dimensions or use CSS to reserve space.
2. Ads and Embeds
Advertisements and embedded content like videos can load asynchronously and push other elements around. To prevent this, reserve space for ads and embeds or load them asynchronously with placeholders.
3. Dynamic Content
Content that loads after the initial page load, such as user comments or product recommendations, can cause shifts. Use skeleton screens or reserve space to stabilize layout during load.
How to Address High CLS Scores
1. Specify Size Attributes
Always include width and height attributes for images and videos. This allows the browser to allocate the correct amount of space during page load.
2. Use CSS to Reserve Space
For dynamic or responsive content, use CSS aspect ratios or min-height properties to reserve space and prevent shifts.
3. Optimize Loading of Ads and Embeds
Implement lazy loading for ads and embedded content, and set fixed sizes where possible to maintain layout stability.
Conclusion
High CLS scores can negatively impact user experience and SEO. By specifying image sizes, reserving space for dynamic content, and optimizing ad loads, you can significantly reduce layout shifts. Regularly monitoring your CLS score helps ensure your website remains user-friendly and search engine optimized.