Page Speed and Core Web Vitals Checker
Run a free website speed test on the same engine as Google PageSpeed Insights. Get your performance score, real-user LCP, INP and CLS, and a prioritized list of fixes, straight from your browser.
Calls the official Google PageSpeed Insights API directly from your browser. Free, no sign-up, and DevDome never sees or stores the results.
Google is loading and measuring the page, this takes 20 to 60 seconds.
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Core Web Vitals thresholds: what counts as good
Google grades every metric in three bands: good, needs improvement and poor. For the three Core Web Vitals it applies the thresholds at the 75th percentile of real Chrome visits over the last 28 days, meaning at least three out of four visitors must hit the good mark. This table is the reference this core web vitals checker uses to rate your results.
| Metric | Good | Needs improvement | Poor | What it measures |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | 2.5 s or less | 2.5 to 4 s | over 4 s | How quickly the largest visible element, usually the hero image or headline, finishes rendering. |
| INP (Interaction to Next Paint) | 200 ms or less | 200 to 500 ms | over 500 ms | How quickly the page responds when a visitor taps, clicks or types. |
| CLS (Cumulative Layout Shift) | 0.1 or less | 0.1 to 0.25 | over 0.25 | How much the layout jumps around while the page loads. |
| FCP (First Contentful Paint) | 1.8 s or less | 1.8 to 3 s | over 3 s | How quickly the first text or image appears on screen. |
| TTFB (Time to First Byte) | 0.8 s or less | 0.8 to 1.8 s | over 1.8 s | How quickly your server sends the first byte of the page. |
| TBT (Total Blocking Time, lab) | 200 ms or less | 200 to 600 ms | over 600 ms | Lab stand-in for INP: how long scripts block the main thread during load. |
LCP, INP and CLS are the three Core Web Vitals Google uses as a ranking signal. FCP and TTFB are supporting diagnostics, and TBT only exists in lab tests, where it stands in for INP because a robot cannot click your page the way a person does.
A one-off page speed test vs continuous monitoring
A speed test is a snapshot. It tells you how the page performed during one visit, on one network, at one moment. Real sites drift: a plugin update ships extra JavaScript, marketing adds a tag, a hero image gets swapped for a 4 MB original, and the score you screenshotted last month quietly stops being true. The sites that stay fast are the ones that keep measuring after the fix.
Speed is also only one axis of site health. A page that scores 95 but sits behind an expired SSL certificate or a down server is still losing every visitor. DevDome Site Health watches uptime and site health around the clock, probing your site every 15 minutes and running daily audits, so you find out about problems before your visitors do.
Page speed and Core Web Vitals FAQ
What is a good page speed score?
Google grades the performance score in three bands: 90 to 100 is good, 50 to 89 needs improvement, and 0 to 49 is poor. The score comes from a lab test, so treat it as a diagnostic, not a grade carved in stone. Aim for 90 plus on desktop and as high as you can get on mobile, where throttled hardware and network make every page slower.
What are Core Web Vitals?
Core Web Vitals are three user-experience metrics Google measures from real Chrome users: LCP (Largest Contentful Paint) for loading speed, INP (Interaction to Next Paint) for responsiveness, and CLS (Cumulative Layout Shift) for visual stability. Google uses them as a search ranking signal, evaluated at the 75th percentile of your real visitors over the last 28 days.
What is a good LCP, INP and CLS?
Good means LCP of 2.5 seconds or less, INP of 200 milliseconds or less, and CLS of 0.1 or less. Poor means LCP over 4 seconds, INP over 500 milliseconds, or CLS over 0.25. Anything between is rated needs improvement. Google applies these thresholds to the 75th percentile of real user visits, so most of your visitors need to hit them, not just the fastest ones.
What is the difference between field data and lab data?
Field data comes from the Chrome User Experience Report (CrUX): real visits by real Chrome users over the last 28 days. Lab data comes from a single simulated page load run by Lighthouse on Google servers. Field data is what Google actually ranks on, but it only exists for pages with enough traffic. Lab data is available for any public URL and is best for debugging, since it is repeatable and includes detailed diagnostics.
Why is my page speed score different every time I run the test?
Lab tests have natural variance: your server load, network routing, third-party scripts, ads and A/B tests all change between runs, and Lighthouse simulates a throttled connection on shared Google infrastructure. Swings of 5 to 10 points are normal. Run the test two or three times and watch the trend. The field data section does not have this problem because it aggregates 28 days of real visits.
Does page speed affect SEO?
Yes. Core Web Vitals are a confirmed Google ranking signal, measured from field data. The bigger effect is usually indirect: slow pages get abandoned before they load, which hurts conversions, ad quality scores and crawl efficiency. Fixing LCP and INP problems tends to pay for itself in revenue before it pays in rankings.
Is this the same as Google PageSpeed Insights?
It runs on the same engine. This tool calls the official PageSpeed Insights v5 API directly from your browser, so you get the identical Lighthouse lab test and the identical CrUX field data that pagespeed.web.dev shows, presented in a cleaner report with plain-English fixes. Nothing is proxied or stored by DevDome.
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