Lighthouse is the audit built into Chrome DevTools and PageSpeed Insights: it loads a page on a throttled simulated device and reports scores plus the specific opportunities behind them — unoptimized images, render-blocking scripts, missing alt attributes, bad contrast. The scores are a lab measurement, which makes them reproducible but not identical to what users experience — that is the field data CrUX collects and what the ranking systems actually consult.
The right reading: use the lab score as a regression test and diagnostics list, not as the goal. A 100 is achievable on a page that still feels slow on a real phone, and a 92 with clean field data is the better outcome. The opportunities list is the value — the number is just the summary.
Related terms
Core Web Vitals
Google's three field metrics for loading, responsiveness and visual stability, measured on real visits rather than in a lab.
LCP (Largest Contentful Paint)
The moment the biggest piece of content in the viewport finishes rendering — in practice, when the page looks loaded.
INP
Interaction to Next Paint — the Core Web Vital that measures how fast a page responds to taps and clicks, replacing FID since 2024.
CLS
Cumulative Layout Shift — the Core Web Vital measuring how much the page jumps around while loading.
The bench this belongs to
Web performanceA rebuild that loads on a phone on mobile data, in the country your customers are actually in. Core Web Vitals are the measurement, revenue is the point.
