Skip to main content
Performance

PageSpeed Insights

PSI | Google PageSpeed

Portrait of Robert Klimant, co-founder of Roelu Studio
Robert KlimantCo-founder

What is PageSpeed Insights?

PageSpeed Insights (PSI) is a free Google tool that analyses how a page performs on mobile and desktop. It combines two data sources: field data from real Chrome visitors over the past 28 days, and lab data from a simulated Lighthouse run. The tool reports Core Web Vitals — LCP, INP, CLS — alongside diagnostics and opportunities for improvement. It is the standard reference for measuring web performance against Google's thresholds.

Why it matters

PageSpeed Insights is the closest thing to a definitive scorecard for web performance because Google built it and Google ranks pages with it. If PSI shows red, your SEO team is fighting an uphill battle. The lab data tells you what is theoretically wrong. The field data tells you what real visitors are actually experiencing — which matters far more. Most teams look at the lab score and stop there. The field data, marked as the Core Web Vitals Assessment at the top, is the one Google uses for ranking. If you check one metric a month on your site, make it that one.

How it works

You paste a URL into pagespeed.web.dev and PSI runs the analysis in about 20 seconds. The report opens with the Core Web Vitals Assessment — pass or fail — based on real-user field data. Below that, a Lighthouse audit shows lab metrics and a list of specific opportunities: unused JavaScript to remove, images to compress, render-blocking resources to defer. Each opportunity shows the estimated time savings. The workflow most teams use: run PSI, fix the top three opportunities, deploy, run PSI again, repeat. Field data updates on a 28-day rolling window, so improvements take a few weeks to fully reflect.

Related terms

  • Lighthouse Score

    Performance

    A 0–100 grade from Google's Lighthouse tool measuring a page's performance, accessibility, SEO, and best practices — used as a quick technical health check by…

  • Core Web Vitals

    Performance

    Google's three benchmark metrics that measure how fast a page loads, how quickly it responds to clicks, and how stable the layout feels as it renders — used in…

  • Page Speed

    Performance

    How quickly a web page loads and becomes usable for a visitor — measured in seconds and milliseconds, and treated by Google as a confirmed ranking signal…

  • Largest Contentful Paint

    Performance

    The Core Web Vital that measures how long it takes for the biggest visible element on a page — usually the hero image or main headline — to finish loading in…

  • Interaction to Next Paint

    Performance

    The Core Web Vital that measures how quickly a page responds when a visitor clicks, taps, or types — Google's official replacement for the older First Input…

  • Cumulative Layout Shift

    Performance

    The Core Web Vital that measures how much a page jumps around visually as it loads — penalising sites where buttons, ads, or content shift unexpectedly under…

  • Image Optimization

    Performance

    Compressing, resizing, and serving images in modern formats so pages load faster without losing visible quality — usually the single biggest performance win…