How to read PageSpeed Insights

This is Chrome UX Report field data: 28 days of real Chrome visits, at the 75th percentile. The pass/fail “Core Web Vitals Assessment” is here, based on LCP, INP and CLS. The toggle switches between “This URL” and “Origin” (the whole domain). If the URL has too little traffic, PSI shows origin data or nothing at all.

This is a fresh Lighthouse run from a Google data centre: a simulated Moto G Power on throttled 4G for mobile, or a desktop on a fast connection. It produces the 0–100 performance score (see how it’s weighted), five lab metrics, a filmstrip, and a list of opportunities and diagnostics with estimated savings. Filter the audits by metric (LCP, TBT, CLS…) to see only what affects the number you care about.

• Server response time varies from request to request.
• Ads, A/B tests and third-party tags load different content each time.
• Google may route your test to a different data centre.
• Lighthouse versions change the audits and occasionally the scoring.

Swings of 5–10 points are normal. Run the test two or three times and take the median, or keep a history and watch the trend.

CoreVitals uses the same PSI API, so the numbers match, but runs mobile and desktop together, keeps your history, compares up to five sites and writes an AI fix plan. For request-level waterfalls from specific locations, WebPageTest is the standard. For monitoring real users continuously, add the web-vitals library to your analytics.