Core Web Vitals

Google uses CWV as a ranking signal, bad scores can hurt rankings, especially on mobile. They're measured in field data (real users) not lab data, so synthetic Lighthouse scores aren't enough on their own.

Targets: LCP under 2.5s, INP under 200ms, CLS under 0.1. Hitting all three on mobile is harder than it sounds because the mobile field-data percentile sees real-world phones and networks, not your developer machine.

The biggest wins come from image optimisation, fewer render-blocking scripts, and avoiding layout shift on font loading. We measure CWV before and after every build.