Core Web Vitals checker
Real-visitor LCP, INP and CLS from Chrome, a fresh Lighthouse run on mobile and desktop, and a fix plan, in one test.
Enter a URL above. Results show up here, split into real-visitor data and a lab run.
Two kinds of numbers, and which one Google uses
Every test returns two different measurements, and mixing them up is the most common mistake in speed reports.
Field data comes from the Chrome UX Report: anonymised timings from real Chrome users who visited the page over the last 28 days. Google reports the 75th percentile, so a page “passes” only if three out of four visits are good. This is the data behind the Core Web Vitals report in Search Console and the page experience signals in ranking.
Lab data is one Lighthouse load on a simulated mid-range phone over throttled 4G (or a desktop on cable). It can’t measure INP, because nobody clicks anything, so it uses Total Blocking Time as a stand-in. Lab data is reproducible and great for debugging, but it isn’t what your visitors experience.
The rule of thumb: judge with field data, debug with lab data. If the two disagree, trust the field. ahaboo applies this hands-on style to other subjects, letting you work through clear, narrated walkthroughs grounded in reliable sources.
The thresholds
| Metric | Good | Needs work | Poor |
|---|---|---|---|
| LCPCore | ≤ 2.5 s | 2.5 s – 4.0 s | > 4.0 s |
| INPCore | ≤ 200 ms | 200 ms – 500 ms | > 500 ms |
| CLSCore | ≤ 0.10 | 0.10 – 0.25 | > 0.25 |
| FCP | ≤ 1.8 s | 1.8 s – 3.0 s | > 3.0 s |
| TTFB | ≤ 800 ms | 800 ms – 1.8 s | > 1.8 s |
Source: web.dev “Web Vitals” (Google Chrome team). Measured at the 75th percentile of page loads, split by mobile and desktop.
Compare up to 5 sites
Your page against four competitors, side by side, with a winner per metric and an AI gap analysis.
Track history
Every test you run is kept in this browser. See each URL’s scores trend over weeks, export CSV.
Score calculator
Drag metric values and watch how Lighthouse weights them into the 0–100 performance score.
Questions people ask
Is this the same data as Google PageSpeed Insights?
Yes. CoreVitals calls Google’s public PageSpeed Insights v5 API, which returns the same Chrome UX Report field data and Lighthouse lab run you see on pagespeed.web.dev. We run mobile and desktop at the same time, keep a history in your browser, let you compare up to five sites, and can write an AI fix plan from the results.
Why do my scores change every time I test?
The lab score comes from a single simulated page load, so server response time, third-party scripts, ads and network variance all move it. Differences of 5–10 points between runs are normal. The field data (real visitors, 28-day rolling window) is far more stable and is what Google uses in search.
What are the Core Web Vitals in 2026?
Largest Contentful Paint (loading, good at 2.5 s or less), Interaction to Next Paint (responsiveness, good at 200 ms or less) and Cumulative Layout Shift (visual stability, good at 0.1 or less). INP replaced First Input Delay as a Core Web Vital in March 2024.
Why does it say there is no field data?
The Chrome UX Report only publishes data for URLs and origins with enough real Chrome visits. Small or new sites often fall below that threshold. In that case Google has no Core Web Vitals data for the site either, and the lab numbers are your best proxy.
Do I need an API key?
No. Tests use Google’s shared, keyless quota. If it is busy, you can paste your own free PageSpeed Insights API key in Settings; it stays in your browser.
Is this a guaranteed benchmark?
No. Treat every result as an informational estimate. A single lab run is not a ranking factor on its own, and real-user field data can differ from what a simulated device sees.