Cumulative Layout Shift

Definition: One of the three core web vitals, Cumulative Layout Shift, seeks to quantify the stability of the page. As a non-page load metric, we understand how much the core of the page shifts as the page loads and as the customer interacts.

Why it's good: CLS answers a few questions. First, customers won't be frustrated that the site is moving as they try to interact. But the less considered is that continued movement of the page appears to customers as perceived slowness.

What to consider: CLS is not a standard metric about performance but more a user experience metric to understand the stability of the page for our customers. For some pages, the more interaction, the higher the CLS. We expect an inverse relationship where a high CLS means higher conversion in these cases. This is not because a high CLS converts better. This is because a highly engaged customer will tend to have a higher CLS but still convert better than a low-engagement customer. Now imagine what happens when you improve CLS for highly engaged customers!