CLS ↔ Cumulative Layout Shift to measure visual stability 👍<0.1 arb

aka Cumulative-Layout-Shift

Layout Shift

when Element in Viewport changes position - any jitter between frames - indicate visual instability, usually unintentional - measure by CLS

CLS should NOT measure user triggered Layout Shift - any lag to user input contributes to FID

CLS should exclude animations & transitions - which are obviously intentional/expected Layout Shift

font load will delay LCP & then add to CLS for 2X kick in the $&#!

fonts.googleapis.com went down! unreliable!

References

1. Web Vitals ↔ metrics to QA test Web Page UX as LCP, FID & CLS vs 75th percentile page loads

2. Layout Shift ↔ when Element in Viewport changes position - any jitter between frames - indicate visual instability, usually unintentional - measure by CLS