Page Speed Test (Lighthouse via PageSpeed Insights)
Lighthouse scores, Core Web Vitals and what to fix first — from Google PageSpeed Insights.
Test a page
API key
- Open Google Cloud Console → APIs & Services → Credentials (sign in with a Google account and create a project if asked).
- Enable the PageSpeed Insights API for that project.
- Choose Create credentials → API key, and restrict the key to the PageSpeed Insights API.
- Paste the key here.
Report
Real users (Chrome UX Report, last 28 days)
Google has no real-user (Chrome UX Report) data for this page or site — usually because it has too little traffic. The lab test below still applies.
Lab test (Lighthouse)
Insights — what to fix first
Sorted by the estimated time saved. Open one for details and the files involved.
Diagnostics
Accessibility, best practices and SEO
About the Page Speed Test (Lighthouse via PageSpeed Insights)
Enter a page address and the tool runs Google's PageSpeed Insights on it — the same Lighthouse test as pagespeed.web.dev — for a mobile or desktop visitor. You get the Performance, Accessibility, Best Practices and SEO scores, the five lab metrics that make up the performance score (First Contentful Paint, Largest Contentful Paint, Total Blocking Time, Cumulative Layout Shift, Speed Index), the insights that would save the most time with the files involved, diagnostics and failed audits for the other categories.
When Google has enough visits to the page or site, the report also shows real-user data from the Chrome UX Report: the 75th percentile of LCP, INP, CLS, FCP and TTFB, how many page loads were good, and whether the Core Web Vitals assessment passes. The request goes from your browser straight to Google; download the full JSON or copy a summary for a ticket.
How to use it
- Enter the page URL (a public address — Google's servers load it).
- Choose Mobile or Desktop and the categories to test, then press Run test. A test usually takes 10–60 seconds.
- Start with Real users: if the Core Web Vitals assessment fails, that is what visitors experience. Then read the lab scores and metrics.
- Open the Insights at the top of the list first — they are sorted by the estimated time saved — and check the files each one names.
- Use Copy summary, JSON or Open on pagespeed.web.dev to share the result. If the shared quota is used up, add your own free API key under API key.
How the performance score is calculated
Lighthouse's performance score (0–100) is a weighted average of five lab metrics: Total Blocking Time 30%, Largest Contentful Paint 25%, Cumulative Layout Shift 25%, First Contentful Paint 10% and Speed Index 10%. Scores of 90–100 are good, 50–89 need improvement and 0–49 are poor (Lighthouse performance scoring). The lab test is one simulated load on Google's servers — mobile tests use a slow network and a slower CPU — so the score varies from run to run.
Core Web Vitals thresholds (real users)
Google measures each metric at the 75th percentile of page loads, separately for mobile and desktop. A page passes the Core Web Vitals assessment when all three are good (web.dev: Web Vitals):
- LCP (loading): good ≤ 2.5 s, poor > 4 s.
- INP (responsiveness): good ≤ 200 ms, poor > 500 ms.
- CLS (visual stability): good ≤ 0.1, poor > 0.25.
Two supporting metrics: FCP good ≤ 1.8 s, poor > 3 s, and TTFB good ≤ 0.8 s, poor > 1.8 s (a rough guide, not a Core Web Vital). Lab tests cannot measure INP, because no real visitor interacts with the page; Total Blocking Time is the lab metric that tracks it best.
About the API key and the quota
PageSpeed Insights is called directly from your browser. Google says the API "can be used with or without an API key", but requests without a key were refused with HTTP 429 and a daily quota of 0, so in practice a key is needed. MySmartCoPilot can use its own free key (shared by all visitors, so it can run out); you can also paste your own key, created in Google Cloud Console in a few minutes. Your key is sent only to Google with each test and is stored on this device only if you tick Remember. Google has also said it plans to stop including Chrome UX Report data in this API; when that happens, the real-user section will be empty (PageSpeed Insights API).
Limitations
- Only public pages can be tested: pages behind a login, on localhost or on a private network are not reachable for Google's servers.
- Lab results vary between runs (network, A/B tests, ads, server load); compare several runs before drawing conclusions.
- Real-user data exists only for pages and sites with enough Chrome traffic; many small sites have none.
- When the shared quota is used up, tests need your own API key or must wait.
Privacy
The address you test (and the API key in use) is sent from your browser to Google's PageSpeed Insights API, which loads that page; Google's terms and privacy policy apply to that request. MySmartCoPilot does not receive or store the address or the results. A key you choose to remember is kept in this browser's local storage only.
Frequently asked questions
Why is my score different every time I test?
Most of the variation does not come from Lighthouse but from changing conditions: network routes, server load, A/B tests, rotating ads and third-party scripts. Lighthouse's documentation suggests thinking of the score as a range; run the test a few times and look at the trend.
Which matters for Google rankings: the lab score or real-user data?
Core Web Vitals are judged on real-user (field) data — the Chrome UX Report section. The lab score is a diagnostic: it explains why a page is slow and what to fix, but it is not a ranking number.
Why is there no real-user data for my page?
The Chrome UX Report only covers pages and sites with enough visits from Chrome users who share usage statistics. When a URL has too little data, Google may show the whole site's data instead; for small sites there may be none at all.
Is this the same as pagespeed.web.dev?
It uses the same PageSpeed Insights API and Lighthouse engine, so results are comparable — but every run is a new test, so numbers differ slightly between runs and tools.
Do I need an API key?
Only when the shared quota is used up (or if this site has no key configured). Creating a key is free: open Google Cloud Console, enable the PageSpeed Insights API, create an API key and restrict it to that API.