PageSpeed Insights (PSI) is a free Google service at pagespeed.web.dev that analyzes a public URL and shows two kinds of data in one report: field data from real Chrome users, and a Lighthouse lab run with prioritized recommendations.
Why it matters
PSI is the quickest way to see both how real visitors experience a page and why. The field section comes from the Chrome User Experience Report (CrUX), covering the previous 28 days at the 75th percentile, and it is the data Google uses for Core Web Vitals assessment. The lab section is a single simulated load, so it is good for debugging but varies from run to run.
Example
How to read a report:
Field data (CrUX): LCP 2.3s INP 180ms CLS 0.05 -> Passed
Lab data (Lighthouse): Performance 64A page can pass in the field while scoring poorly in the lab, or the reverse. Passing the field assessment is the goal; the lab score guides fixes.
Common misconceptions
- Low-traffic pages always show field data. CrUX needs enough visits, otherwise PSI may show origin-level data or none.
- The lab score is the ranking signal. Field Core Web Vitals are.
- It tests behind a login. It only reaches public pages.
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