Why is my CLS value poor even though the page loads quickly?

CLS measures something entirely different from loading speed, namely visual stability. A page can load lightning-fast and still have a poor CLS value if elements keep jumping around after the first render. Typical culprits are: images and videos without a fixed width/height attribute, late-loaded web fonts that trigger a font swap, dynamically inserted banners or cookie consent layers that push content downward, and animations that modify layout properties instead of the GPU-friendly transform property.

The insidious part is that these shifts often only become visible on slower connections, exactly where you are not looking when testing your own site. In our performance analysis we track down every single layout shift, attribute it to the triggering element and fix the root cause in a targeted way, for example by reserving space for images and ads or preloading fonts.