Comparison
Cumulative layout shiftvsSkeleton screen
Cumulative layout shift
you went to click the button, an ad loaded above it, and you clicked something else entirely.
A score accumulating every unexpected movement of visible content, weighted by how much moved and how far. The usual causes are images without dimensions, webfonts swapping, and content injected above existing content. Shifts within 500 milliseconds of a user interaction are excluded, which is why opening an accordion does not count and an ad slot filling in does.
Full entry →Skeleton screen
you show grey blocks the shape of the content instead of a spinner while the data loads.
A placeholder that mimics the layout of the content that is coming. It improves perceived speed and, more usefully, reserves the space so nothing shifts when the real content lands. It becomes a liability when the skeleton's shape does not match the result, which turns one layout shift into two.
Full entry →