Core Web Vitals Checker (Real-User CrUX Data)

About the Core Web Vitals Checker (Real-User CrUX Data)

The Chrome UX Report (CrUX) is Google’s public dataset of how real Chrome users experience websites: how fast the main content appeared, how quickly the page responded to taps and clicks, and how much the layout jumped. It is the field data behind Search Console’s Core Web Vitals report and the real-user section of PageSpeed Insights.

Enter a page or a whole site (its origin) and the checker looks it up in the CrUX API for all devices, phones, desktops and tablets. For each of LCP, INP and CLS — the three Core Web Vitals — and for FCP and TTFB, it shows the 75th-percentile value, its rating and the share of good, needs-improvement and poor page loads, and whether the page passes the Core Web Vitals assessment. Weekly history draws up to 40 weekly periods, so you can see whether a fix worked, and Many URLs checks up to 25 pages or sites in one go. Requests go from your browser straight to Google.

Without a pass you see a free preview: the Core Web Vitals verdict for each device with its first metrics in full, the weekly charts watermarked with the first weeks of their table, and of many URLs the first ones. The full results, and copying or downloading them, unlock with a Pro pass.

The thresholds

Each metric is judged at the 75th percentile of page loads, so three in four visits are at least that good (web.dev: Web Vitals, Defining the Core Web Vitals thresholds):

• LCP (Largest Contentful Paint, loading): good ≤ 2.5 s, poor > 4 s.
• INP (Interaction to Next Paint, responsiveness): good ≤ 200 ms, poor > 500 ms.
• CLS (Cumulative Layout Shift, visual stability): good ≤ 0.1, poor > 0.25.
• FCP (First Contentful Paint): good ≤ 1.8 s, poor > 3 s (web.dev: FCP).
• TTFB (Time to First Byte): good ≤ 0.8 s, poor > 1.8 s — a rough guide, not a Core Web Vital (web.dev: TTFB).

A page passes the Core Web Vitals assessment when LCP, INP and CLS are all good. When one of the three has no data, the checker says so instead of guessing.

Where the data comes from

The CrUX API returns a rolling 28-day aggregate of real visits by Chrome users on desktop and Android who have opted in (usage statistics reporting and history sync turned on), updated once a day; the CrUX History API returns up to 40 weekly 28-day periods (about ten months), updated weekly. A page (URL) record covers that address only; an origin record covers every page of the site under that scheme and host — https://www.example.com and https://example.com are different origins. Only publicly discoverable pages (status 200, not marked noindex) with enough Chrome traffic have data (CrUX methodology). The values are statistics about visits, not a test: to find out why a page is slow, run a lab test with the Page Speed Test.

The diagnostics

• LCP image breakdown: for pages whose largest element is an image, the 75th percentile of each part of LCP — time to first byte, the delay before the image starts loading, its load time, and the delay before it is drawn. The parts are separate percentiles, so they don’t add up exactly to LCP.
• LCP element: how often the largest element was an image or text.
• Navigation types: how visits reached the page — a normal navigation, a reload, back/forward (from the back/forward cache or not), a prerender.
• Round-trip time: the 75th percentile of the network round-trip time of visitors, a sign of how fast their connections were.

About the API key and the quota

The CrUX API only answers requests that carry an API key, and allows 150 lookups a minute per Google Cloud project, at no charge. A check uses four lookups (all devices, phone, desktop, tablet) and the weekly history one more. If MySmartCoPilot’s shared key is not available or its quota is used up, you can use your own key: in Google Cloud Console, enable the Chrome UX Report API and create an API key (restrict it to that API). Your key is sent only to Google with each lookup, and kept on this device only if you tick Remember.

Limitations

• Only public pages and sites with enough Chrome traffic in the last 28 days have data; many small sites have none, and many pages only have data for the whole origin.
• The data is about real visits in the past 28 days, so a fix shows up gradually; the weekly history is the way to follow it.
• Opted-in Chrome users on desktop and Android only: Chrome on iPhone and iPad, other browsers (including other Chromium-based browsers) and in-app web views are not in the Chrome UX Report.
• The list mode checks up to 25 addresses at a time, for one device.

Privacy

Sends data to online services

The address you check (and the API key in use) is sent from your browser to Google’s Chrome UX Report API; Google’s terms and privacy policy apply to that request. MySmartCoPilot does not receive or store the address or the results. A key you choose to remember is kept in this browser’s local storage only.