The only three performance metrics we track religiously
LCP, INP, CLS. Everything else is noise until these are green.
Every new client site we take over is haunted by the same pattern: a dashboard full of vanity metrics, and a homepage that takes four seconds to render on a mid-range Android.
We only care about three numbers.
1. LCP — Largest Contentful Paint
Target: under 2.5s on 4G, mid-tier device.
The usual suspects: un-optimized hero images, blocking fonts, render-blocking scripts
dropped in <head>. Fix those three and you'll ship 80% of LCP wins.
2. INP — Interaction to Next Paint
Target: under 200ms.
The metric that replaced FID in 2024. Catches the jank users actually feel — slow tap responses, laggy dropdowns, the kind of stuff that makes a site feel "cheap" without anyone being able to articulate why.
3. CLS — Cumulative Layout Shift
Target: under 0.1.
Reserve space for images and ads. Ship web fonts with size-adjust. Don't insert content
above the fold after first paint. That's most of CLS.
What we ignore
- Page weight in KB — it's a proxy, not a metric.
- TTFB — matters, but mostly a hosting / SSR problem, which is solved for us on Amazon Web Services (AWS).
- Lighthouse scores — useful during dev, not worth chasing in prod.
Three numbers. One dashboard. Green or not green.