Google's free tool for measuring page performance and Core Web Vitals in the lab and the field.
Official siteGoogle PageSpeed Insights (PSI) is a free tool that analyses a URL and reports how fast it loads and how it performs, on both mobile and desktop. It combines two data types: lab data from a single Lighthouse run, and field data — real Chrome user measurements from the Chrome UX Report (CrUX) — for the site's actual Core Web Vitals.
The field data is what matters for SEO, because Core Web Vitals (LCP, INP and CLS) are a Google ranking signal, and PSI shows whether real users pass them. The catch: CrUX field data only appears for pages with enough Chrome traffic, and the lab score is a single snapshot that can vary run to run, so it is a guide, not a guarantee.
PSI runs Lighthouse and surfaces CrUX field data to score performance and diagnose what to fix.
PSI is the performance-diagnosis layer for technical SEO. It overlaps with the Core Web Vitals report in Search Console, but PSI works on any single URL and adds Lighthouse-level detail on how to fix it. In dev workflows the Lighthouse engine underneath PSI runs locally and in CI.
Strength: free, authoritative on Core Web Vitals (it uses the same CrUX data Google ranks on), and specific about fixes. Limit: lab scores fluctuate between runs and can mislead if over-weighted; field data is missing on low-traffic pages; and the score is not a direct ranking multiplier — passing Core Web Vitals is the goal, not chasing a perfect 100.
We use PSI field data to confirm whether real users pass Core Web Vitals, then work the lab diagnostics into our technical-SEO and web-dev backlogs. We validate against the Search Console Core Web Vitals report and CrUX rather than fixating on a single Lighthouse score.
PageSpeed Insights (PSI) is Google's free page-performance tool, and it is important because it reports both lab and field data for a URL in one place — including the real-user Core Web Vitals Google actually uses for ranking. It matters as the go-to first check on a page's speed and page-experience health, and crucially it distinguishes the two kinds of data most people conflate: the simulated Lighthouse lab score, and the 28-day real-user field data from the CrUX dataset. Reading both correctly is the difference between chasing a vanity lab number and fixing what Google actually measures.
PSI shows two datasets and they answer different questions. The field data (labelled as real-user experience, from the Chrome User Experience Report) is the 75th-percentile of actual Chrome users over 28 days — this is what determines whether a page passes Core Web Vitals for ranking. The lab data comes from a single Lighthouse run in a controlled environment and is useful for debugging and reproducing issues, but it is a simulation, not what Google ranks on. The classic mistake is optimising to make the Lighthouse score green while the field data still fails; PSI's value is showing you both so you optimise the right one.
Use PSI as a first diagnostic: enter a URL, read the field data to see whether it genuinely passes Core Web Vitals, then use the Lighthouse lab diagnostics and opportunities to identify what to fix — render-blocking resources, oversized images, main-thread blocking, layout shifts. Fix the underlying issues (often via development work on the rendering path, image pipeline and JavaScript), then re-verify. Because field data lags 28 days, confirm real-world improvement in Search Console's Core Web Vitals report over time rather than expecting the field number to move instantly. PSI diagnoses; the fixes usually live in the code.
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