Out of all the metrics, it is probably easiest to identify a site with poor CLS as this signifies a very annoying customer experience! CLS is measuring the largest layout shift scores for every unexpected layout shift that occurs during the lifespan of a page.

Sites with poor CLS likely have pop-ups, text that shifts, ‘Click Me’ buttons and other fast-moving elements that a user will likely find frustrating. In particular, sites that are not optimised for mobile devices will likely fail on this metric

A good CLS score should be 0.1 or less, with 0.25 or under needing improvements and another above classed as poor.