Google’s Core Web Vitals are the standard for measuring a website’s performance. However, not all browsers support these metrics. In this article, we clarify which metrics are available across the most popular browsers.
What browsers support the three Core Web Vitals metrics?
All Core Web Vital metrics are supported by Chromium browsers. Chromium is an open-source web browser project developed by Google. Some of the most popular browsers that are based on Chromium are: Chrome, Microsoft Edge, Samsung Internet, and Opera.
Chromium browsers on iOS will not report Core Web Vital data.
But what about other popular browsers, such as Safari and Firefox? These are non-Chromium browsers and support for metrics varies between them.
For example, Largest Contentful Paint is supported by Firefox but not by Safari.
There are a few metrics which are supported across all browsers:
From these 4 metrics, First Contentful Paint is the only one which measures a visitor's experience. The other three are technical metrics.
In the table below, you can see an overview of which metrics are available in each of the browsers mentioned in this article.
If you want to verify whether a metric is available in a browser not listed in the table, caniuse.com offers current information. In the example below we can see the current availability of LCP.
Can page weight be measured for real users?
Browsers do report page weight data for resources loaded from the current websites. DebugBear real user monitoring has a dedicated dashboard for first-party page weight.
However, third-party transfer size is not available as browsers withhold this information for security reasons.
Why am I seeing metrics reported in browsers that don’t support them?
Core Web Vitals data can appear in non-Chromium browsers when users use a Chromium based browser with a non-Chromium user agent.
In the screenshot below we can see website visitors using a user-agent in Safari, with Core Web Vital data being collected.
Conclusion
Understanding which browsers support Core Web Vital metrics will provide context when analyzing RUM data.
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