Free Core Web Vitals checker
Enter a URL to get its Core Web Vitals from Google's own measurement — LCP, INP and CLS, mobile and desktop separately. Where Google has real-user data for the URL, that is what you see, and the tool says plainly when it is falling back to a lab test.
Field data and lab data are not the same number
This is the distinction most speed tools blur, and it changes how much the result is worth. Field data comes from the Chrome UX Report: actual visits from actual people over a rolling 28 days, reported at the 75th percentile — meaning three quarters of your visitors had an experience at least this good. That is the data Google uses when Core Web Vitals influences ranking.
Lab data is one Lighthouse run on Google’s hardware with a simulated connection. It is repeatable and useful for comparing before and after a change, and it is not what anyone experienced. Field data only exists for URLs with enough traffic to report, so a new or quiet page will always fall back to lab. The tool labels which one you are reading rather than presenting them as interchangeable.
What each metric is telling you
LCP is when the biggest visible thing finished rendering, usually the hero image or the headline. A slow LCP is nearly always one of four things: a slow server response, a render-blocking stylesheet or script, an unoptimized image, or a font that holds text invisible while it loads. Good is under 2.5 seconds.
INP is how long the page takes to respond visibly after a tap or click, measured across the whole visit rather than just the first interaction. It is a JavaScript problem almost every time — long tasks on the main thread that leave the browser unable to paint. Good is under 200 ms.
CLS is how much the layout jumps around while loading. Images without width and height, ads that expand on arrival, and fonts that swap to a different size are the usual causes. It is the cheapest of the three to fix and the most irritating to experience. Good is under 0.1.
Mobile is the number that counts
Google indexes with a mobile crawler, and mobile results are usually substantially worse than desktop — slower CPU, slower network, smaller viewport that changes which element is the largest. A page that passes on desktop and fails on mobile is failing, which is why both are shown here and why the mobile column is the one to fix first.
Where speed actually sits
Core Web Vitals are a genuine ranking signal and a small one. They mostly break ties between pages that are otherwise comparable — a fast page will not outrank a better answer. The stronger argument for fixing them is that people leave slow pages before any of this matters.
Speed is also only one layer of what determines whether people reach a site. The free website audit measures Core Web Vitals alongside crawlability, metadata, structured data, security headers, accessibility and AI search visibility, then scores the result — and what counts as a good score explains how to read that number.
Core Web Vitals questions
- What are Core Web Vitals?
- Three measurements Google uses to describe page experience: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness, and Cumulative Layout Shift for visual stability. They are a small part of ranking, and a large part of whether a visitor stays.
- What is a good LCP score?
- Under 2.5 seconds is good, 2.5 to 4 needs improvement, and over 4 seconds is poor. LCP measures when the largest visible element finishes rendering — usually the hero image or the main heading. It is the closest single number to 'how long until this page looks loaded'.
- What is INP and what replaced FID?
- Interaction to Next Paint replaced First Input Delay as a Core Web Vital in March 2024. FID only measured the delay before the first interaction started processing. INP measures the full time from an interaction to the next frame being painted, across the whole visit, which is much closer to what a user actually experiences. Good is under 200 ms.
- What is the difference between field data and lab data?
- Field data comes from the Chrome UX Report — real visits from real people over the last 28 days, reported at the 75th percentile. Lab data is one synthetic test on Google's hardware. Field data is what Google uses for ranking, and it is only available for URLs with enough traffic to report. This tool tells you which one you are looking at.
- Why does the tool show TBT instead of INP?
- INP cannot be measured in a lab, because it requires real people interacting with the page. When field data is unavailable, Total Blocking Time is reported instead — it measures how long the main thread was blocked during load and is the best available proxy for how sluggish interactions will feel.
- Do Core Web Vitals affect rankings?
- Yes, as a real but small factor. They function mostly as a tiebreaker between pages of comparable relevance — no amount of speed will outrank a genuinely better answer. The larger effect is on conversion: slow pages lose visitors before ranking ever enters into it.
- How do I improve Core Web Vitals on WordPress?
- On WordPress the biggest wins usually come from a caching plugin, an image optimizer that serves properly sized modern formats, and removing render-blocking scripts from heavy page builders and unused plugins. Measure before and after with field data, since a fast-looking admin preview does not reflect what real visitors experience.
- How do I improve INP?
- Interaction to Next Paint improves when you reduce the amount of JavaScript that runs in response to a tap or click, so break up long tasks, defer non-essential scripts, and avoid heavy work on the main thread during interactions. INP measures real responsiveness, so third-party tags and unused code are common culprits.
- What causes a poor CLS score?
- Cumulative Layout Shift is caused by elements moving after the page starts rendering — typically images and ads without reserved space, web fonts that swap late, or content injected above what the user is already reading. Setting explicit width and height on images and reserving space for embeds fixes most of it.
- How do I improve my LCP?
- Largest Contentful Paint improves when the main image or heading block loads quickly, so serve a compressed, correctly sized hero image, avoid lazy-loading it, and cut the server response time that delays everything after it. Removing render-blocking CSS and JavaScript before the main element also helps.
- How long does it take for Core Web Vitals changes to show in Google?
- Google's Core Web Vitals report uses field data from the CrUX dataset, which is a 28-day rolling average, so improvements take up to about a month to fully appear. Lab tools like this one show the effect of a fix immediately, which is why you use lab data to iterate and field data to confirm.
- Do Core Web Vitals matter for mobile and desktop separately?
- Yes — Google evaluates mobile and desktop as separate experiences and reports their field data separately, and mobile usually scores lower because phones have slower processors and networks. Since Google indexes the mobile version first, the mobile scores are the ones to prioritise.