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What are Core Web Vitals?

This post looks at Core Web Vitals, essential metrics by Google that assess a webpage's user experience focusing on loading, interactivity, and visual stability.

Updated: 06/06/2024

Core Web Vitals are a set of specific factors that Google considers important in a webpage’s overall user experience. Core Web Vitals are measured as part of Google’s “page experience” score.

Imagine it as the web equivalent of a body’s vital signs, when a doctor does a check up to see how healthy you are. This is a “check up” to see how healthy your website is.

Why are Core Web Vitals important?

Core Web Vitals are important because page experience is an official ranking factor [1] (that’s how Google determines if you are number one on a search page).

What are the factors of Core Web Vitals?  

Loading SpeedThe time it takes for a website host to send the website data to your browser.
Time to InteractivityThe time it takes for a website to become usable.
Visual StabilityHow much of the website shifts around on the page as it loads.  

Website Speed

You may have noticed two out three of the Core Web vitals are about speed. Users (and search engines) want Websites that are fast like an olympic sprinter, not a slow sluggish website that takes a long time to get to the point. 

Largest Contentful Paint (LCP)

Google measures loading speed as a “content paint” as if your web browser is ‘colouring’ in the website. The best practice here is for a page to load within 2.5 seconds.

Time to Interactivity or First Input Delay (FID)   

Time to Interactivity is measured in the delay to the first input (eg click, scroll, etc). Having a website loaded quickly as described above, is good. However, if you can’t click anything or move around the page, it’s technically still loading and not a good user experience. The best user experience means your webpage should be interactive (usable) in 100 milliseconds or less (that’s 0.1 second, scary huh?).

Fast websites sprinting to the #1 finish

Fast websites sprinting to the #1 finish

Slow websites need a performance boost

Let’s reiterate the point again with a little more stress, the Speed of your Website is Very Important. 

Visual Stability 

It’s very frustrating to use a website where elements move about as you’re using it. Imagine a sudden pop-up pushing down the cancel button you were trying to click and you accept something you didn’t want to. 

Cumulative Layout Shift (CLS)

Google measures visual stability as Cumulative Layout Shift (CLS) and ideally there should be minimal movement in website elements. A score of 0.1 (or less) is the bar to pass.

An example of a late loading button that pushes content further down. 

 Are there Secondary Web Vitals?

Mobile FriendlinessHow usable is the website on a smartphone
Safe BrowsingNo malware on your website
HTTPS Website data is sent securely (encrypted)
No Intrusive InterstitialsNo pop-ups that block the whole page and stop user interaction

Mobile Friendliness

Website mobile friendliness is a term used to describe how well a website functions and looks on a variety of mobile devices, such as phones, tablets, and eReaders. Being mobile friendly means that websites can adjust their content and layout to accommodate the needs of users on mobile devices.

If a website is not mobile friendly, text and images might be unreadable, too small. The layout might be awkward or buttons might be difficult to click with your finger because they are too close together.   

Safe Browsing

One of the worst things you can do is put malware on your website. This is unlikely to happen to you unless you are a victim of a cyber attack. However sometimes legitimate software can be flagged as Malware so it’s worth checking.


Websites secured over HTTPS provide better security and privacy. HTTPS websites use SSL (Secure Socket Layer) encryption, which encrypts the data that is sent between the server and the user’s browser. This means that the data is secure and cannot be intercepted by third parties. Additionally, HTTPS websites provide authentication, which ensures that the user is connected to the correct server and not a malicious one. This is a clear sign that the website owner is actively trying to run a reputable website and a necessary indicator of website health.

No Intrusive Interstitials

Intrusive Interstitials are web page pop-ups that block most or all of a page, leading to a bad user experience for both desktop and mobile users, because they make it difficult for the user to access the content that they want. Intrusive interstitials are often used as advertisements and can be quite annoying for the user.

A pop up blocking a users onward journey is not healthy for your website

Click me

Running a Core Web Vital test 

Google’s Core Web Vitals Tester is a powerful tool that can help users measure the performance of website pages. The tool measures the Core Web Vitals (and secondary web vitals listed above), providing detailed feedback and insights into how your website is performing.

It’s as simple as copy / pasting your web address into the checker and clicking analyze! 

Core Web Vitals test example

Search Console

You can also find your site’s Core Web Vitals data in the “experience” section of your Google Search Console account.

Channel: Search Marketing

Digital Project Manager
Digital project manager for Lighthouse and a Lecturer at Harper Adams University . He can be contacted through LinkedIn or the Lighthouse contact page

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