User experience and SEO optimization with Web Core Vitals

by | Nov 16, 2020 | Application Performance, Articles

Google introduced Web Vitals as new real user experience monitoring metrics in May 2020. They bring together user experience and SEO optimization.

Boris Rogier

Boris Rogier


Web Core Vitals to track user experience

Google introduced Web Vitals as new real user experience monitoring metrics in May 2020. They bring together user experience and SEO optimization. In 2021, it will be part of the metrics driving your SEO, so you’d better understand its impact on your digital performance. 

What does it mean from a digital experience monitoring standpoint? How can it help you improve your SEO performance?

End user experience is what really matters

For years, web performance has focused on metrics like Page Load Time (PLT), which measures how fast a web page loads.

Improving loading times has always been the utmost goal to achieve.

But one important question remained unanswered: “If a website seems slow according to the performance metrics, how does a real user experience this?” 

Browser metrics vs User Experience metrics

To provide an answer to this question, let’s take the example of a website that uses lot of Javascripts (like most websites these days). 

To start, Javascripts are “DOM blocking” components (except if you are deferring them or asynchronously loading them). This means they must be rendered to consider that the whole page has been loaded (which drives the PLT).

Techniques like asynchronous or deferred Javascripts allow the browser to load the Javascripts in a lazy way without impacting the DOM parsing process. This means that the scripts will be loaded at the end. Using these techniques can greatly improve the user experience.

Nevertheless, the PLT (Page Load Time) will not reflect it as the document load will not be complete until all Javascripts are loaded.

The problem with metrics like PLT (Page Load Time) is that they are “browser-centric”. As a conclusion, to measure the user experience, we need more “user-centric” metrics.

First step towards measuring user experience: loading speed

RUM (Real User Monitoring) is a common way to collect web performance metrics. As part of its evolution, metrics like First Contentful Paint (FCP) and First Meaningful Paint (FMP) came into play to complement PLT to improve the evaluation of user experience.

  • FCP measures the time when the first content (first text or image) is rendered on the user’s screen.
  • FMP measures the time for the first piece of content which is meaningful to a user.

Unfortunately, FMP has been overly sensitive to small differences in the page load, leading to inconsistent results. Even if FCP remains a good metric, the first content may not be meaningful for the end user.

We should use other metrics to evaluate how real users experience a page load speed.

Speed Index and Visually Complete are two good examples. Unfortunately, these metrics are only available through synthetic monitoring / synthetic testing.

Overall this left us with no practical way to measure user experience.

Integrating interactivity and visual stability in the user experience

Measuring page load speed is not enough: introducing Interactivity and Visual stability in your evaluation of the digital experience.

Interactivity (First Input Delay)

First, being able to quickly interact with a website (for example by clicking on links or buttons) is as important as rapidly getting useful information on the screen.

If you really want to measure how real users experience your website, measuring the speed of loading resources is not enough. This is only the first part of the story. Of course, getting useful content on the screen quickly is key, but how fast you can interact too. Interactivity is also a critical factor.

Visual stability (Cumulative Layout Shift)

Second, when a page loads, the loading of an image can potentially change the whole page structure, including text. Assume you begin to read an article while the page is still loading: the text structure will be altered and shifting around. This generates a bad experience. Visual Stability is a 3rd critical factor.

As a conclusion, if you are serious about optimizing user experience on your site, you have to take 3 major factors in account:

  1. Loading speed: How fast is the page loading and how fast does the user see meaningful content?
  2. Interactivity: How fast can the page react to user input?
  3. Visual stability: Does stuff move around while the page is loading?

Welcome Web Vitals

Early May 2020, Google announced Web Vitals: a thoroughly researched set of metrics to help quantify the experience of websites and identify opportunities to improve.

Within those new metrics introduced by Google Page Experience, there is a subset of metrics every site owner should focus on: Core Web Vitals. According to Google, “Site owners should not have to be performance gurus in order to understand the quality of experience they are delivering to their users. The Web Vitals initiative aims at simplifying the landscape, and help sites focus on the metrics that matter most, the Core Web Vitals.”

The current set of metrics focuses on the three aspects mentioned above:

A successor of FCP, LCP measures the time when the largest piece of content within the viewport is rendered. In fact, this metric helps answering multiple questions:

  1. First, is there any content on the screen?
  2. Second, is this content meaningful?
  3. Third, is this content rendered fast on the page?

It measures how long it takes for the site to react to the first interaction by a user.

It measures the shifts in layout while a page is loading.

Finally. What’s also cool about these new metrics is that Google provides corresponding baselines, as illustrated hereunder (picture from Google):

Using web core vitals to measure digital experience

Boost your SEO too!

So far, Google’s SEO ranking considered the following factors:

  • Mobile-friendliness: make sure your site is optimized for mobile users
  • HTTPS: ensure secure connections to you website
  • Interstitial use: stay away from annoying pop-ups
  • Safe browsing: make sure your site does not represent any risk for visitors

In 2021, Google’s SEO ranking calculation will take add the new Web Vitals metrics to the list and take them into consideration.

Combined, these metrics make up what’s Google calls the “page experience”, as illustrated hereafter (picture from Google).

Web core vitals within digital experience metrics

So, do not wait any longer and start measuring Web Vitals metrics right now so that you are ready to boost your SEO in 2021!

Recap and next steps

The web performance field is moving from pure browser-centric metrics to new types of user-centric metrics to better align with real user experience.

After first attempts with metrics like FCP and FMP, Google is now promoting Web Vitals; a new set of metrics that considers each step of a complete user experience.

Even if these new metrics are mainly supported by Chromium-based systems, there is no doubt other major players will align and adopt them in the near future.

These metrics will be taken into consideration for SEO rankings in 2021. Measuring them and taking corrective action to improve them right now will assure a good SEO ranking position in the future.

Start measuring Core Web Vitals with Kadiska Now!

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