PageSpeed Insights

What it measures

Paste a URL into PageSpeed Insights (PSI) and it returns two kinds of data, for mobile and desktop.

Field data comes from the Chrome User Experience Report: what real users experienced over the previous 28-day collection period, for First Contentful Paint, Largest Contentful Paint (LCP), Interaction to Next Paint (INP) and Cumulative Layout Shift (CLS). Small or new sites may not have enough traffic to show field data.

Lab data comes from Lighthouse running the page in a simulated device and network. It produces scores for Performance, Accessibility, Best Practices and SEO, plus a list of opportunities and diagnostics. According to Google's PSI documentation (checked 2026-09), the Performance score comes from this lab run: 90 and above is good, 50 to 89 needs improvement, below 50 is poor.

The Core Web Vitals thresholds

web.dev defines the "good" thresholds, measured at the 75th percentile of page loads (as of 2026-09):

• LCP: 2.5 seconds or less (how quickly the main content appears)
• INP: 200 milliseconds or less (how quickly the page responds to taps and clicks; INP replaced First Input Delay as a Core Web Vital in 2024)
• CLS: 0.1 or less (how much the layout jumps around)

How site builders use it

On WordPress, Shopify and Webflow sites, the usual culprits show up quickly in the report: huge hero images, too many apps or plugins injecting scripts, web fonts blocking text, sliders, and third-party chat or tracking widgets. A good workflow is to test the home page, a product or service page and a blog post before you change anything, save the results, make one change at a time and retest. Show the client the before and after; it is concrete evidence of the work.

Reading it sensibly

• Field data is what users actually felt; prefer it when it exists.
• Lab scores vary between runs, so test a few times and look at the trend.
• A score of 100 is not the goal. Passing Core Web Vitals and a site that feels fast on a mid-range phone on a mobile network is.
• Lighthouse suggestions are hints, not orders; some (such as removing a payment script) are not options for a store.

Prerequisites and time

None. Each test takes under a minute. Understanding the metrics well enough to fix them takes longer; web.dev's Core Web Vitals articles are the companion reading.

Common questions

Why does my site score differently in Chrome DevTools? DevTools Lighthouse runs on your machine and network; PSI runs on Google's servers with its own throttling.

Can I test a site behind a login or on localhost? No, PSI needs a public URL. Use Lighthouse in Chrome DevTools for local testing.