Glossary · CLS (Cumulative Layout Shift)
CLS (Cumulative Layout Shift)
A Core Web Vitals metric measuring how much page content visually shifts during loading.
CLS quantifies unexpected layout shifts (text moving when an image loads, buttons jumping when an ad renders). Good CLS is under 0.1; needs improvement is 0.1–0.25; poor is over 0.25.
Common CLS fixes: reserve space for images and ads with width/height attributes, avoid inserting content above existing content, use CSS transforms for animations.