Cumulative Layout Shift (CLS)

Cumulative Layout Shift (CLS)Cumulative Layout Shift (CLS) measures how much visible elements shift unexpectedly during loading and represents the visual stability of a page.Open glossary entry → is one of the Core Web VitalsCore Web Vitals are a set of Google metrics that measure real-world user experience in the areas of loading performance, interactivity and visual stability.Open glossary entry → and measures how much visible elements move unexpectedly while a page loads. Such jumps disrupt the user experience, for example when a button shifts at the last moment. A good CLS value is no more than 0.1.

A poor CLS is often caused by images without width and height attributes, ad slots without reserved space, embedded videos without placeholders, banners that load late, cookie banners or web fonts. You can improve CLS by:

• specifying width and height on images so the browser can reserve space,
• reserving space for ads and embeds,
• positioning cookie banners in a stable way,
• optimising font loading and using placeholders (skeletons),
• not inserting late-loading content above already visible content.