What Lighthouse checks
Lighthouse runs an automated audit of a page and reports categories including performance, accessibility, best practices, and search optimization. For performance it loads the page in a controlled environment, records timings, and combines several metrics into a single weighted score from zero to one hundred.
- It simulates a mid tier device and a throttled network by default.
- It measures real metrics like paint and interaction delay.
- It returns specific opportunities and diagnostics, not just a score.
Reading the result wisely
The headline number is a weighted blend, so two pages with the same score can have very different problems. Always open the opportunities and diagnostics sections, because those tell you which fix returns the most benefit. A lab audit runs once on one machine, so results vary between runs.
- Lab data comes from a single controlled run and is repeatable for debugging.
- Field data comes from real users and reflects actual conditions.
- Treat the score as a compass, then trust real user measurements for ground truth.
Run several audits and look at the median rather than reacting to one unlucky run.
Key idea
A Lighthouse audit gives a weighted lab score plus concrete opportunities, so use the breakdown for fixes and lean on field data for the real verdict.