Short answer: PageSpeed Insights (free, by Google) reports real-user Core Web Vitals from Chrome users over the last 28 days plus a Lighthouse lab audit on one emulated phone. MobileCheck (free) renders the page on up to 51 phone and tablet profiles, iPhones in Safari's engine, and marks readability problems on screenshots. Use PageSpeed Insights for speed, MobileCheck for layout.
PageSpeed Insights and MobileCheck are both free and both start with a page address, so they are easy to confuse. They answer different questions. PageSpeed Insights asks "how fast is this page, for real visitors and in a lab test?" MobileCheck asks "how does this page look and read on phones, and what is hard to use?" If you only run one, you miss half the picture.
What PageSpeed Insights does
PageSpeed Insights is Google's free page speed tool. It shows two kinds of data:
- Field data from the Chrome User Experience Report (CrUX): Largest Contentful Paint, Interaction to Next Paint, Cumulative Layout Shift and First Contentful Paint, from real Chrome users over the previous 28 days, reported at the 75th percentile. When a single page has too little data, it falls back to the whole origin. Pages that are new, not public or not popular enough have no field data.
- Lab data from Lighthouse, which loads the page once on an emulated mobile device with throttled CPU and network (and once as desktop), and scores four categories: Performance, Accessibility, Best Practices and SEO.
The Lighthouse accessibility audits include color contrast and a check that the viewport tag doesn't block zoom. There is also a PageSpeed Insights API for automated checks. Lighthouse itself is open source and runs in Chrome DevTools, where it can audit local and logged-in pages.
One detail worth knowing: CrUX collects data from Chrome on desktop and Android only. Chrome on iOS is excluded, and so is Safari, so iPhone visitors are not in the field numbers.
That makes the two tools complementary rather than competing: PageSpeed Insights covers what Chrome visitors experienced over the past month, and MobileCheck covers what a visitor on a given screen sees today, iPhones included.
What MobileCheck does
MobileCheck loads your page on any or all of 51 device profiles — iPhones and iPads in WebKit, Safari's engine, Android devices in Chromium — and checks each one in normal view, dark mode, 150% text and with the mobile menu opened. The report shows full-page screenshots, a 0–100 score, and every problem marked where it is: text size, contrast, tap targets, content wider than the screen, the viewport tag, disabled zoom, clipped or overlapping text. It also measures LCP, CLS and page weight, but only as a lab reading from our server over a fast connection, not real-user data.
At a glance
| PageSpeed Insights | MobileCheck | |
|---|---|---|
| Main question | How fast is the page? | Does the page work on phones? |
| Real-user data | Yes, CrUX (Chrome users, 28 days) | No, lab only |
| Core Web Vitals | LCP, INP, CLS from the field, plus lab metrics | Lab LCP and CLS, no INP |
| Devices per run | One emulated phone, one desktop | Up to 51 phones and tablets |
| Browser engine | Chromium | WebKit for iPhones and iPads, Chromium for Android |
| Screenshots | Loading filmstrip and a final screenshot | Full-page screenshot per device with problems marked |
| Dark mode, 150% text, open menu | No | Yes |
| Accessibility | Broad audit (labels, ARIA, contrast and more) | Contrast, text size and tap targets as seen on each device |
| Cost | Free | Free |
When PageSpeed Insights is the better choice
- You care about Core Web Vitals as Google measures them. The field numbers come from the same CrUX data Google uses; no lab tool, ours included, replaces them.
- You need INP. Responsiveness to taps needs real interactions, which only field data captures.
- You are tuning performance. Lighthouse's diagnostics — render-blocking resources, unused JavaScript, image sizes — go far deeper than our three numbers.
- You want a broad accessibility and SEO audit, including form labels, ARIA and document structure, which MobileCheck doesn't cover.
- You want to automate it through the PageSpeed Insights API or Lighthouse in CI.
When MobileCheck is the better fit
- The page is fast but looks broken on some phones. PageSpeed Insights tests one screen size; a menu that overflows at 360px or a heading that wraps badly on an iPad won't show up there.
- Your visitors use iPhones. MobileCheck renders iPhones in Safari's engine, and our Safari vs Chrome comparison shows where the engines differ.
- You want to see dark mode and larger text. These are settings many people use every day; see our guides on dark mode and large text.
- You need to show someone the problem. A screenshot with the small text boxed is easier to act on than an audit name.
How to use both together
- Run PageSpeed Insights first to see whether real users are having a slow experience, and which Core Web Vitals fail.
- Run MobileCheck on the same page across the device range to catch layout and readability problems.
- Fix speed with Lighthouse's diagnostics and layout with the report's fixes, then re-check both. Field data updates over the following 28 days, so give it time.
Google retired its Mobile-Friendly Test in 2023 and pointed people to Lighthouse; read more in our note on the alternative.
Frequently asked questions
Does PageSpeed Insights check if a site is mobile friendly?
Partly. Its Lighthouse audit runs on one emulated phone and checks things like contrast and the viewport tag, but it doesn't show how the page looks across many screen sizes, in Safari's engine, in dark mode or with larger text.
Why do MobileCheck and PageSpeed Insights show different LCP?
They measure differently. PageSpeed Insights field data is the 75th percentile of real Chrome users, and its lab test throttles the CPU and network. MobileCheck measures once from our server over a fast connection, so its numbers are usually lower.
Is MobileCheck made by Google?
No. MobileCheck is an independent free tool and is not affiliated with Google. PageSpeed Insights and Lighthouse are Google products.