Lighthouse
Lighthouse is “an open-source, automated tool to help you improve the quality of web pages” (Google) — the measurement instrument beneath much of this wiki’s performance discussion, which had the metrics (core-web-vitals) but not the tool that audits them. Source: Chrome for Developers.
How it works
Point it at a URL; it “runs a series of audits against the page, then generates a report” with 0–100 scores across performance, accessibility, SEO, best practices. Runs from Chrome DevTools, a Node CLI, the web UI (PageSpeed Insights), or a browser extension. Performance metrics reported: FCP, Speed Index, LCP, TBT, CLS.
Lab vs. field — the key caveat
Lighthouse is lab data: a controlled, single synthetic run — not real-user field data (the CrUX dataset behind core-web-vitals-wordpress-astro‘s rankings and Google’s actual ranking signal). The two routinely disagree, which matters for this wiki’s recurring tension: a great lab score and a poor field score can coexist. Use Lighthouse to diagnose (budgets can be enforced via Lighthouse-CI), CrUX to judge.
Related
core-web-vitals · performance-budget · page-weight · core-web-vitals-wordpress-astro · web-almanac