CLS (Cumulative Layout Shift)

A Core Web Vital that measures how much the page layout shifts while loading.

Cumulative Layout Shift (CLS) is a Core Web Vital that measures visual stability — how much the layout unexpectedly shifts during page load. Each shift is scored by its impact fraction and distance fraction. Google's "Good" threshold is a CLS score below 0.1. Common causes of high CLS include images without defined dimensions, ads that load dynamically, and web fonts causing FOIT/FOUT.