Definition
CLS
A measure of unexpected layout movement while a page loads.
Definition
Cumulative Layout Shift, or CLS, measures how much visible content unexpectedly shifts position during the page lifecycle.
Meaning
It captures the frustrating experience where text, buttons, forms, or images move after a visitor starts reading or clicking.
Why It Matters
Poor CLS can cause misclicks, reduce trust, and make a page feel unstable. It is one of Google's Core Web Vitals.
History And Context
Google introduced CLS as part of Core Web Vitals in 2020 to make visual stability a mainstream web quality metric.