Web Vitals land in Cloudflare Browser Insights

Cloudflare has been pushing the idea that performance work has to start with real measurement. Last year the company launched Browser Insights to give its customers that visibility from the end user's perspective. Now, in partnership with the Google Chrome team, Browser Insights can collect the three Core Web Vitals metrics that Google has been advocating as the essential gauge of user experience.

The core argument behind Web Vitals is that traditional performance metrics don't capture what users actually experience. Time to First Byte (TTFB) and similar network-level measurements are useful, but they only tell part of the story. Google's Web Vitals framework breaks user experience into three components:

  • Loading: How long until content is available?
  • Interactivity: How responsive is the page when the user interacts with it?
  • Visual stability: How much does the page shift around while loading?

The three corresponding Core Web Vitals metrics are Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS).

From high-level signals to root causes

Web Vitals are designed as a starting point, not the final answer. They tell you what is going wrong at a high level, but you still need more granular data to understand why. The narrative works like this: if LCP looks bad, you dig into navigation timing metrics like DNS lookup time and TTFB. From there you might adjust cache hit rates, tune the origin server, or change the order in which JavaScript and CSS resources load.

Browser Insights continues to measure those underlying navigation timing metrics alongside the new Core Web Vitals, keeping the full diagnostic chain intact. For guidance on fixing specific problems, Google has published optimization guides for LCP, FID, and CLS.

Why Browser Insights for RUM data

Real User Measurement (RUM) complements synthetic testing in an important way. Loading a page from a dev machine tells you little about how it behaves on varied devices and network connections. RUM captures that real-world variation by reporting from actual visitors.

Google's own Chrome User Experience Report (CrUX) aggregates data for the whole web and feeds tools like Page Speed Insights. But CrUX data is a 28-day rolling average, so changes take weeks to show up. Cloudflare positions Browser Insights as a complementary alternative for three reasons:

  • Freshness: New data points appear shortly after a request from an end user.
  • Browser coverage: Browser Insights measures any browser, not just Chromium. The APIs needed to report Web Vitals are currently supported only in Chromium browsers, but Safari and Firefox support will follow when those APIs land.
  • Cost: Browser Insights is free, including for high-traffic sites, with analytics built for speed.

The tool also supports slicing and grouping by URL, browser, OS, and country, with more dimensions planned.

Enabling and what's next

Web Vitals metrics are available immediately to all Browser Insights users. To turn it on, go to the Speed tab in the Cloudflare dashboard. The service injects a JavaScript beacon into HTML pages; you can restrict which pages or hostnames it loads on. For CSP version 3 deployments, Cloudflare automatically detects and applies the nonce when one is present.

Cloudflare says work is underway to extend Browser Insights to all Web Analytics customers, including those who don't use Cloudflare at all. Upcoming features include client-side error reporting and diagnostic tools aimed at making the fix-it step more direct. The company has also spent the past year reworking the dashboard's analytics to stay responsive even for its largest customers, and it remains free.