CLS (visual stability)

CLS stands for Cumulative Layout Shift. It does not measure how many seconds a page takes to load: it measures visual stability. An unexpected shift happens, for example, when a late-loading image pushes down a button someone was about to press.

Hypothetical example: you are completing a demo request and a banner moves the form. This is frustrating for people; an agent using visual positions may interact with the wrong element. Not every agent navigates in the same way.

To spot the problem, watch the journey during loading, including on a slow connection. Note which element moves and which content appears before the shift. A recording helps your team reproduce the user’s experience.

Reserving space for images, ads and later-loading content helps prevent movement. These are practical priorities: ask your team to measure behaviour before and after under comparable conditions, rather than only changing appearance.

Chrome’s documentation connects layout shifts with agents identifying an element before clicking it. Reducing CLS alone does not prove that a form is understandable, that data was saved or that conversions improved: check each outcome separately.