CLS

Cumulative Layout Shift (CLS) is a Core Web Vital that measures the total amount of unexpected layout movement that occurs during the lifespan of a page. A high CLS means elements shift around as the page loads, creating a frustrating user experience.

Google considers a CLS score below 0.1 good. Common causes include images without defined width and height attributes, ads or embeds loaded without reserved space, and web fonts that swap during load and push text around.