What is Cumulative Layout Shift?
We’ve all experienced seeing a link we want to click on a website while it’s still loading, and going to click it but then the website “shifts” and you click the wrong link (or worse, start a loud video!). This is layout shift, and cumulative layout shift is the total time it takes for your website to load so that no further shifts happen.
Large images and video are the most common cause of layout shift. Because eCommerce sites can have a lot of images, this score can be hard to improve on. Having set size attributes for images and videos, or ensuring your theme uses “transform” to set image parameters will minimize shift.
To provide a good user experience, sites should strive to have a CLS score of 0.1 or less.