Lighthouse vs CrUX for Core Web Vitals:

Lighthouse vs CrUX for Core Web Vitals:
The mistake I see weekly: optimizing the wrong one. I checked both on a slow client page.

Lighthouse (lab)
➕ Repeatable, controlled — great for A/B testing a fix before you ship
➕ Tells you WHY (specific blocking scripts, unused CSS)
➖ Synthetic; my Lighthouse LCP was 1.8s while real users saw 3.4s

CrUX / field data
➕ Real Chrome users — this is literally what Google ranks on
➕ 75th-percentile is the number that counts for the ranking signal
➖ 28-day rolling, so fixes take weeks to show; no per-page "why"

Best for: diagnosing + testing a fix → Lighthouse. Knowing if you actually pass → CrUX.

Price-vs-value: both free. The trap is celebrating a green Lighthouse while CrUX stays red — only CrUX moves rankings.

Pick Lighthouse to debug. Skip it as your scoreboard — use CrUX field data for that.

Tested on a real, live page.