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Core Web Vitals checker

Enter a URL to see how real Chrome users experience it (LCP, INP, CLS at the 75th percentile) and a fresh Lighthouse lab run. Powered by Google’s PageSpeed Insights API.

The three Core Web Vitals

LCP — Largest Contentful Paint. How long until the main content (hero image, headline) is visible. Good: up to 2.5 s; poor: over 4 s.
INP — Interaction to Next Paint. How quickly the page responds when someone taps, clicks or types. Good: up to 200 ms; poor: over 500 ms. It replaced FID in March 2024.
CLS — Cumulative Layout Shift. How much the layout jumps around while loading. Good: up to 0.1; poor: over 0.25.

Google looks at the 75th percentile of real visits: a page passes when at least 75% of experiences are “good” on all three.

Field data vs. lab data

Field data comes from the Chrome User Experience Report (CrUX): anonymized measurements from real Chrome users over the last 28 days. It is what Google uses for search, but it only exists for pages and sites with enough traffic.

Lab data is a Lighthouse run on Google’s servers with a simulated device and network. It is reproducible and great for debugging, but it can’t measure INP (there is no real user interacting) and it may differ a lot from what your visitors see.

Monitor your own visitors, every day

CrUX only covers Chrome users, updates over a 28-day window and skips smaller sites. Analisa’s script measures LCP, INP, CLS and FCP on every visit, in every browser that supports them, and shows them per page next to traffic, sources and conversions — so you can see whether a slow page is costing you signups. It works without cookies and the SDK is about 4 KB. See how to install it.

Frequently asked questions

Why is there no field data for my page?

CrUX only publishes data for URLs and origins with enough Chrome traffic in the last 28 days. Smaller or new sites often have none; measuring your own visitors with a real-user monitoring tool fills that gap.

Why is my Lighthouse score different every time?

Lab tests depend on server load, network conditions and third-party scripts at that moment. Variations of a few points are normal; look at trends and at field data instead of a single run.

Do Core Web Vitals affect Google rankings?

Yes, as part of Google’s page experience signals, based on field data. They act more as a tie-breaker than a dominant factor, but slow pages also convert worse, which matters regardless of rankings.

What replaced First Input Delay (FID)?

Interaction to Next Paint (INP) became a Core Web Vital in March 2024. It measures responsiveness across all interactions on the page, not just the first one.

Is there a limit to how many pages I can test?

To keep the tool free we limit checks per network and cache each result for an hour. For continuous monitoring of every page, use a real-user monitoring tool.

Web Vitals from every real visit

Analisa tracks LCP, INP and CLS per page alongside traffic and conversions — no cookies. Free up to 10K events a month.

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