Where Web Vitals Leaderboard Gets Its Data and How Often It Updates

Web Vitals Leaderboard pulls its numbers from the Chrome UX Report (CrUX) API, which reflects how real Chrome users actually experience sites on the web. The data is a 28-day rolling average, so any result you see represents the past 28 days of aggregated metrics rather than a live snapshot. This matters if you're using the leaderboard to judge whether your site is genuinely faster or slower than competitors: you're comparing a recent monthly trend, not a single test run.

The data source: Chrome UX Report (CrUX)

The leaderboard doesn't run its own synthetic tests. Instead, it queries the CrUX API, a Google dataset built from real-world Chrome users.

• Real user data, not lab data. CrUX captures field metrics from actual browsing sessions, so it reflects real devices, networks, and conditions rather than a controlled test environment.
• Aggregated by origin and URL. CrUX groups user experience metrics by origin (e.g., example.com) and by specific URL, for all websites known to Google's crawlers.
• Coverage depends on Google's crawlers. A site only appears if Google's crawlers know about it and enough real users visit it to produce reportable data.

Why you might see "Chrome UX report data not found!"

If the leaderboard returns that message, it means CrUX has no reportable data for the origin or URL you entered. Common reasons:

• The site is too new or gets too little Chrome traffic to meet CrUX's reporting thresholds.
• The origin isn't recognized by Google's crawlers.
• You entered a URL or origin that doesn't have aggregated data.

In that case, the leaderboard has nothing to rank — it isn't a bug in the tool so much as a gap in the underlying dataset.

How often the data updates

CrUX data is a 28-day rolling average of aggregated metrics. In practice:

• At any given moment, the numbers represent the past 28 days combined, not the last hour or day.
• The window slides forward over time, so results gradually change as older data drops out and newer data comes in.
• Because it's an average, a single slow day won't swing your score dramatically, and a single fast day won't either.

This is useful for trend comparison but means the leaderboard won't show the effect of a change you deployed minutes ago. If you just shipped a performance fix, expect the rolling average to reflect it only gradually.

How rankings are determined

The leaderboard ranks sites using Web Vitals metrics, with Largest Contentful Paint (LCP) as the most important for representing speed.

• LCP measures when a user perceives that the largest content of a page is visible — the time between the page load starting and the primary content rendering.
• Based on real website data, top-performing sites render LCP in about 1.2 seconds, which is the benchmark the ranking leans on.
• Other metrics shown alongside LCP include FCP, CLS, and INP, giving a fuller picture of loading, stability, and interactivity.

What this means for interpreting results

Use the leaderboard when you want an industry-relative, real-user view of performance over roughly the last month. Don't use it to validate a change you made today, and don't treat a missing result as a failing grade — it usually just means CrUX lacks enough data for that origin or URL.