What are Core Web Vitals and Why are They Important?

As Google continues to make numerous updates, businesses and users are constantly wondering how their core web vitals are performing. Yet even more users do not even know what core vitals are.


Let’s Start from the Beginning: What are Web Vitals?

Web Vitals were started by Google to improve user experience. It allows businesses and developers to see how their website measures and compares to other websites by zeroing in on core metrics. Google has various amount of resources and ways to view data to see how their website is performing. However, all these resources can sometimes be complicated and overwhelming. That’s why streamlining the information into three key metrics allows the website owner to see what to prioritize in terms of improvement. Plus, at the end of the day, the goal is always to improve user experience, so wouldn’t it make sense for Google to focus on metrics that do just that?

The Core Web Vitals

These key metrics, or core web vitals, are applicable to all pages on a website.  Since the whole goal of having core web vitals is to better the user experience, they are measured using data from real human experience, not robots. Each website is tested and receives a score for each web vital. The scores have certain levels, so if the website receives a low score it fails for that vital. If it receives the required score or higher, it passes. As of May 2021, Google updated what the core web vitals are and their required scores, as developers prepare to ensure that their sites will all pass. In order to have a functioning website that is prosperous in Google’s eyes, it is very important to analyze the three core web vitals, which are centered around the metrics of loading, interactivity, and visual stability.


The Largest Contentful Paint, or LCP, is the metric that measures loading time. Therefore, Google measures this based on the largest component on the page, which tends to be a banner image or a large block of text. However, it is important to note that Google does not measure LCP using anything “behind the fold” or far enough down the page where it would require the user to scroll. So, whether the user is on a mobile device or a desktop, Google will take the largest image viewable without the user scrolling. In order to receive a passing LCP score, the largest component must load in 2 seconds or less 75% of the time.

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The final core web vital is the Cumulative Layout Shift (CLS). This measures the visual stability of a website. To test a website’s visual stability, Google examines its layout when absolutely nothing has moved on the page. CLS tests this to determine if the site moves unexpectedly when no events occurred. Let’s look at it this way: have you ever been on a website, maybe shopping or filling out a form, and right when you are about to click “send” or “confirm payment” the site glitches, the page jumps down, and you hit the wrong button? If so, then you know how important visual stability is because that is beyond frustrating! So, to improve user experience, Google tests make sure that the layout of the site does not have these random shifts. To score, Google calculates the total percentage of the page affected by the percentage of the page it moves (area x distance moved).

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FID, or First Input Delay, measures a web page’s activity. This response time metric is measured from the time a user clicks, searches, or requests data from a page, to the time it takes for the requested action to be acknowledged. However, let’s clarify that Google is not measuring when the user visually sees the change. Rather, it is measuring the time between the event (when you input the data) and how long it takes for the web page to begin processing the requested event.

In order to pass, Google requires that it take 100 milliseconds or less between the time of the event and when it begins processing. FID is typically the least problematic of the three core web vitals and most web pages pass without any issues. The only time there may be an issue is if there is too much on the backend, such as a variety of plugins. Sometimes too many unnecessary plugins can slow down the response time. Therefore, if you do fail this goal (or are close to failing), start by checking the amount of plugins and their functions, because odds are that is the source of the problem.

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The Goal to pass is to have a CLS of 0.1 or less. Now if your website has one or two minor shifts, then you should be fine. However, if 100% of your page moves 25% down, then that would be a fail. Additionally, it is important to note that CLS measures percentages – not pixels which means the results can differ drastically on a mobile device. With all of these web vital goals, it is important to examine the impact of a mobile device because not only can it differ from a desktop experience, but many users will be accessing your website through mobile devices, which is why it is incorporated into the web vitals score.

How To Check Your Core Web Vitals’ Data

So, all of this information is great, but how can it actually be tested? The best way to check your core web vitals’ data is by using Google Search Console. Unlike other platforms, it measures the real “human” data. This data was not created using robots and since all of these core web vitals are dependent on real-life user experience, this is perfect. Though if the site is not live or is lacking traffic to the point where you can’t access real-life data, you can go to Google’s Page Speed Insights Tool. This isn’t as accurate because it’s artificial data, but it will give you a good representation of the metrics. (Note that you cannot obtain FID data from Page Speed Insights because it must be measured using real-world data. However, you can look at the Blocking Time in Page Speed Insights, as that data correlates with FID and can give you an idea of how your FID is performing). If you want more technical, in-depth data, you can also go to Chrome’s Dev Tools. This is source can be beneficial for web developers.

As stated previously, there have been a lot of new changes and implementations to Google core web vitals, so it is important now more than ever to make sure that your website is performing adequately.