CLS (Cumulative Layout Shift)
CLS (Cumulative Layout Shift)
Cumulative Layout Shift tracks every unexpected layout shift that occurs on the page.
Out of all the metrics, it is probably easiest to identify a site with poor CLS; they 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. If content is constantly popping up or moving around the page, this can be annoying for users.
An example of a website with lots of pop-ups. This could make the experience annoying for users and result in a low CLS score.
A good CLS score should be 0.1 or less, with 0.25 or under classed as needs improvement and any higher classed as poor.