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Core Web Vitals: out with the old, in with the new?

This spring, Google’s Chrome team revealed the new page experience metrics it was defining. Three new Core Web Vitals will carry weight in the Google search algorithm in 2021. But will other web performance metrics become obsolete? And what about browser APIs like Navigation Timing?

Core Web Vitals: new page experience metrics

May 2020 looked like spring cleaning time for web performance metrics. In recent years, the focus has been on devising ways to evaluate user experience, above and beyond measuring milliseconds between variously defined starting and ending points. Nowadays the catchword is page experience.

The first set of ‘Core’ Web Vitals (i.e. Web Vitals that are central to all web experiences) are LCP (largest contentful paint), FID (first input delay), and CLS (cumulative layout shift). Respectively they measure the user’s experience of page loading, page interactivity, and page stability.

New algorithm for Google SERP

As regards its search engine results pages (SERP), Google will add these three new Core Web Vitals as inputs into its new page ranking algorithm, while demoting the AMP mobile experience metric. The change will be official when the Google Page Experience Update is rolled out in 2021.

This is why it is important to measure how your pages perform in terms of LCP, CLS, and FID right away, so you can optimize them accordingly.

What about traditional timings and other Web Vitals?

Page speed measures and other technical metrics (including DOM Ready, Page Load time, DNS Lookup, TTFB, and others), were never intended to be measurements of real-world user experience. The different timings (navigation, server, resource, etc.) gathered in the lab will continue to play a ‘vital’ role in delivering the information that is needed to understand and improve page performance. When technical teams drill down through Core Web Vitals and new page experience signals, they will still home in on the timings represented in waterfalls.

Furthermore, metrics that represent mobile-friendliness are valuable indicators of how things are going for mobile users. Just because AMP will have less weight in Google’s new algorithm doesn’t make mobile page performance any less important!

Field and lab measurements: RUM and synthetic monitoring

Metrics are sourced in two ways: in the field and in the lab. Ideally these two sources are combined to bring performance into sharpest focus. This is why we have real-user monitoring (RUM) to capture real-world page experience in the field, and synthetic monitoring to perform batteries of reproducible tests in the lab. Lab tests (synthetic or active monitoring) are associated with technical metrics like timings and so forth. Similarly, real-user monitoring goes with page experience indicators.

Measuring on both fronts doesn’t have to be complicated. All you need is the right tool, namely, one that can source metrics:

  • in the field on real devices and
  • in the lab with a high degree of representativeness.

The table below shows what you get using some tools that are commonly available in the market.


Ask our web performance specialists what Ekara can do for you. They will show you how to measure the new Core Web Vitals and more in any technical environment and real user context.

LCP, FID, CLS: an evolution, not a revolution

So does Google’s Web Vitals program mean the end of web performance metrics as we know them?

The answer is no.

Core Web Vitals and the Google Page Experience Update set value on how satisfying an experience a page delivers to visitors. The new signals are a work in progress, and are intended to evolve over time. They’re not out to erase the metrics we have been using to improve technical performance, nor will the pertinence of page content be neglected in search results.

Google is the market-leading giant, uncontestably, but it’s not the only search engine out there. Other engines have their own values and approaches that they continue to defend and refine. Furthermore, even if Chromium browsers, which natively support Web Vitals, account for a hefty chunk of the market, they are not alone in the wide world of browsers. In 2021 it will be just as important as ever to measure all page experience via all search engines, on desktop and mobile devices using any browser – let’s not forget Safari – and browser version, whether or not (or until) they integrate APIs to report Google’s Web Vitals.