PageSpeed Insights

A Google tool combining Lighthouse lab data with CrUX field data for any public URL. Shows both diagnostic scores and real-user metrics.

Category: Performance (also: Devops, SEO)

Author: Atomic Glue Performance Team

## Definition

PSI at pagespeed.web.dev provides a dual view: lab data from Lighthouse (performance score, diagnostics) and field data from CrUX (real-user LCP, INP, CLS, FCP, TTFB). It is the official tool Google recommends for evaluating CWV pass/fail.

## Dual-Data Approach

Lab Data: Lighthouse scores from a simulated run. Field Data: CrUX data from real Chrome users over 28 days. If a URL has under ~1,000 visits, field data is empty.

## Common Misunderstandings

Many developers look only at the Lighthouse score and ignore field data. Field data is the authoritative source for CWV pass/fail. PSI showing Good field LCP but Poor lab LCP is common and means real users have faster connections than the Lighthouse simulation.

## Origin vs URL

PSI shows data at origin (entire domain) or URL level. Origin aggregates all pages. URL reports are more actionable.

## Note

Public data. Anyone can look up any URL. 28-day rolling window for field data. Recent optimizations may not appear immediately.

## Common questions

Q: Why no field data?

A: URL needs at least ~1,000 visits in CrUX dataset.

Q: Can I use PSI for auth pages?

A: No. Only publicly accessible URLs. Use RUM or Lighthouse CLI.

## Key takeaways

• Combines Lighthouse (lab) and CrUX (field).
• Field data is authoritative for CWV.
• Needs ~1,000 visits for field data.
• 28-day rolling window.

## Related entries

• [Lighthouse](atomicglue.co/glossary/lighthouse)
• [CrUX Report](atomicglue.co/glossary/crux-report)
• [Core Web Vitals](atomicglue.co/glossary/core-web-vitals)

Last updated July 2026. Permalink: atomicglue.co/glossary/pagespeed-insights