Run a page through PageSpeed Insights and you will see a section called "field data", sometimes with a green tick and sometimes with a message saying there is not enough data. That section comes from the Chrome UX Report, usually shortened to CrUX.

It is one of the most useful and most misunderstood sources of website performance data, because it is Google's own.

The short answer: CrUX is Google's public dataset of how real Chrome users experience websites. It is where the "field data" in PageSpeed Insights comes from, and it is the real-visitor measure Google uses when it assesses Core Web Vitals.

What the Chrome UX Report is

CrUX is a dataset of real-world experience collected from Chrome browsers. It is not a test. Nobody loads your page on a simulated device. It records what actually happened when real people visited, on their own phones and laptops, over their own connections.

Google makes it available through its own tools and to third parties, which is why you meet it in PageSpeed Insights and in Search Console's Core Web Vitals report.

What it measures

CrUX reports the Core Web Vitals, plus a couple of supporting metrics:

LCP (Largest Contentful Paint): how quickly the main content appears. Google's "good" threshold is 2.5 seconds or less.
INP (Interaction to Next Paint): how quickly the page responds when someone taps or clicks. "Good" is under 200 milliseconds.
CLS (Cumulative Layout Shift): how much the page jumps around while loading. "Good" is under 0.1.
FCP and TTFB: when something first appears and how quickly the server responds.

A page or site passes the Core Web Vitals assessment when the 75th percentile of LCP, INP and CLS are all "good". In plain English: at least three out of four visits have to be good, not just the average one. If there is not enough INP data, the assessment uses LCP and CLS.

A rolling 28 days

PageSpeed Insights reports CrUX figures over the previous 28 days. That has two practical consequences:

It lags. If you fix a slow page today, the field data will not fully reflect it for weeks.
It smooths out bad days. One slow afternoon will not ruin your result, but a genuine problem will show up if it lasts.

What CrUX does not cover

CrUX is valuable, but it has limits you should know about:

Chrome only. It reflects Chrome users who have the relevant browser settings enabled. Visitors on other browsers, and Chrome users who have not opted in, are not in it. It is a sample, not a count of everyone.
It needs enough traffic. Google only includes pages and sites with enough visitors to produce a statistically meaningful result. Everything else simply is not represented.
It is not your data. You cannot split it by your own pages, campaigns or customer segments the way you can with measurements taken on your own site.

Why small sites often see "no data"

If your site is a local business, a charity or a new project, you may well see a message that there is not enough field data. That is normal, not a fault. It means your site does not yet receive enough Chrome traffic for Google to publish a result.

It also means PageSpeed Insights falls back to lab data only, which is a single simulated visit. That is useful for finding causes, but it cannot tell you whether real visitors have a good experience. (We cover the difference in why your PageSpeed score differs from what your visitors experience.)

Does CrUX matter for SEO?

Google says good Core Web Vitals align with what its ranking systems aim to reward, alongside other page experience factors. It does not say how much weight they carry compared with the relevance of your content, and it does not promise that a good score will improve your rankings.

So treat it as a foundation, not a trick. Fast, stable pages are better for visitors and are less likely to hold your search visibility back. They will not make up for content that does not answer what people are looking for.

Three sources, three jobs

CrUX (Google's field data): real Chrome users over a rolling 28 days. It is Google's own, independent measure, but it needs enough traffic, lags behind your changes and covers Chrome only.
Your own real-visitor data: real visitors on your site, on any browser, available as soon as they arrive and split by page and device. It only covers your own site.
A lab test (Lighthouse): one simulated visit. It finds specific, fixable causes, but it is not real experience.

They work best together. CrUX is the independent check, your own data fills in when CrUX is silent, and the lab test explains why.

What to do with this

Look at the field data first in PageSpeed Insights, and in Search Console's Core Web Vitals report if you use it.
If it says "not enough data", do not panic. Measure your own visitors instead, so you are not relying on a single lab run.
Give fixes time. Expect weeks, not days, before CrUX reflects a change.
Use the lab diagnostics for causes, such as oversized images or heavy scripts, and the real-visitor data to decide whether they matter.

For a plain-English guide to the metrics themselves, see what are Core Web Vitals.

How we use it

Web Vitals Collector measures your own visitors directly, and also shows Google's CrUX figures in your PageSpeed results where Google has enough data for your site. Where it does not, we say so plainly instead of leaving a gap. Our FAQ has a short version of this, and our sample report shows what a weekly report looks like.

PageSpeed, Lighthouse and CrUX results are automated estimates and are not a guarantee of search ranking.