Track the Core Web Vitals history of a site

How to use the tool

Enter the address of a site or a page, with or without “https://”, pick the scope and the device, then run it. With “whole site”, the tool queries the origin, meaning all the pages of the domain. With “single page”, it queries the exact address you entered.¹

The result has three blocks, one per metric. Each gives the latest value at the 75th percentile with its badge, a 25-week curve drawn against the “good” threshold, the split of visits into three classes for the latest period, and a week-by-week table of values.

What the history contains

For each metric, the CrUX History API returns a series of periods. Each period covers a 28-day window, and periods are spaced one week apart, so they overlap, a bit like a moving average.¹ A fix you ship therefore shows up fully in the curve only after four weeks, once the older visits have left the window.

The default series has 25 periods, and the API accepts up to 40 per request. Google updates it on Mondays around 04:00 UTC with data up to the previous Saturday, with no service level agreement on timing.¹ The tool requests the 25 periods, from oldest to newest.

The three metrics and their thresholds

There are three Core Web Vitals. Largest Contentful Paint (LCP) measures when the largest visible element appears, with a “good” threshold of 2.5 seconds. Interaction to Next Paint (INP) measures responsiveness to clicks, taps and key presses, with a threshold of 200 milliseconds. Cumulative Layout Shift (CLS) measures unexpected movement of content, with a threshold of 0.1.²

Google recommends looking at the 75th percentile of page loads, separately for mobile and desktop.² That is why the tool makes you pick a device: an average of the two would blend two different experiences. The dashed green line on each curve marks the “good” threshold. The limits of the “needs improvement” and “poor” classes (4 seconds, 500 milliseconds and 0.25) are those of the histogram the API returns.¹

Reading the curves and the split

The curve follows the 75th percentile week after week: when it sits under the green line, three quarters of visits do better than the threshold. Google specifies that these values are computed from the full set of available data rather than from the histogram classes.¹ Each point is coloured by its class, so the weeks where the site slipped stand out at a glance.

The split bar shows, for the latest period, the share of good, moderate and poor visits. It complements the percentile: a site that passes the threshold has at least 75% of good visits, and up to a quarter of moderate or poor ones. When a week has too little data, Google returns an empty value, and the tool leaves a gap in the curve instead of joining the neighbouring points.¹

Why Google sometimes has no data

CrUX data comes from real Chrome users on desktop and Android who have turned on usage statistics reporting and synced their history. Chrome on iOS, Android WebView apps and other browsers, Edge included, do not contribute.³

A page or a site must also be public and popular enough. Pages that return errors or are noindex are excluded, and Google does not publish the visit threshold.³ A small local site therefore often has no data, and the tool says so. In that case lab testing is the only benchmark left, and it is done with the PageSpeed test.

Does speed matter for rankings?

Google writes that Core Web Vitals are used by its ranking systems, and that there is no single signal: several page experience signals come into play. Good scores do not guarantee a first place.⁴

Google adds that Search always seeks to show the most relevant content, even when the page experience is sub-par. Experience matters most when many helpful pages answer the same query.⁴ For a brochure site, the curve mainly serves visitors: tracking the history lets you check that a fix held and that an update broke nothing.

What the tool does, and its limits

The tool calls the queryHistoryRecord method of the CrUX API with the three metrics, 25 periods and the chosen device type. A site below the visit threshold is not in the dataset: the API then answers that it has no data, and the tool says so.³ It only handles LCP, INP and CLS; the other CrUX metrics, such as First Contentful Paint, are not shown.

Local, private and credentialed addresses are refused. No address you enter is kept beyond the 6-hour cache, which only holds public measurements from Google. The data does not cover your page alone when you pick the whole site: it aggregates every page of the origin.

After the history

A curve that drops calls for a diagnosis. The PageSpeed test gives lab measurements and fixes to try, and the on-page SEO audit checks the rest of the page. Speed is also one of the points of the checklist for auditing your website. When the fixes need technical work, that is the frame of the SEO support I run for my clients.

Frequently asked questions