You’re more than likely using Google Analytics to measure your website's performance. But are you utilising Core Web Vitals? If not, you should be.

What is Google Core Web Vitals?

Google Core Web Vitals is a powerful tool that provides important page speed insights. It gives valuable Core Web Vitals metrics about your web pages’ overall user interactive experience. It uses a specific set of factors that are part of Google’s Page Experience score that rate the overall UX.

Based on real world web usage data from the Chrome User Experience, the Core Web Vitals report displays page performance metrics. Google refers to this real-world data as ‘field data’ and uses it to also power the engine behind this feature.

The report is based on URL performance grouped by status. It's a ranking Google uses to classify which category of performance a group of URLs’ belong to.

  • Red = Poor
  • Green = Good
  • Yellow = Needs improvement

Google Core Web Vitals uses three main metrics in its report:

  1. Largest Contentful Paint (LCP)
  2. First Input Delay (FID)
  3. Cumulative Shift Layout (CSL)

1. Largest Contentful Paint (LCP)

Largest Contentful Paint is the amount of time it takes to render the largest page elements visible in the viewport, from when the user lands on your web page or requests the URL. These elements are typically an image or video, a large block of text etc.

One of the main contributors to a poor page experience is content load time. This is the amount of time it takes for content to render on a web page. The more content, the longer a web page takes to load, and that’s frustrating for visitors to your website.

The LCP measures how long it takes for the largest page element in the viewport to become visible. This helps Google understand when the main content of the page is rendered and is displayed on the screen. The optimum LCP speed is less than 4 seconds.

Some LCP flags to look out for are:

  • Slow server response times
  • Render-blocking JavaScript and CSS
  • Slow resource load times (<img>, <image> in side <svg>, <video> tags etc.)
  • Client-side rendering
LCP Image  

2. First Input Delay (FID)

First Input Delay  measures the amount of time it takes for a page to become interactive from the time a user visits it. For example, when a link is clicked, a button tapped, or a custom JavaScript-powered control is used.

FID measures the user's real time data to capture the first impressions of your website's interactivity and responsiveness. It tracks the time from the moment somebody interacts with a web page to the time when the browser responds to that interaction. The optimum FID speed should be less than 100 milliseconds.

Although there may be many reasons why FID might be slow, the main cause for poor interaction time is:

  • Heavy JavaScript execution
  • Unminified JavaScript
  • Polyfills
FLD image  
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3. Cumulative Layout Shift (CLS)

'Content jank' or Cumulative Layout Shift represents the time it takes page layouts to shift even after the page has loaded.

CLS measures the visual stability of your content by adding shift scores across layout shifts that don’t occur within 500ms of user input. It looks at how much visible content shifted in the viewport as well as the distance the elements impacted were shifted. The optimum CLS speed is less than 0.25 seconds.

Most common causes of a poor CLS are:

  • Images without dimensions
  • Ads, embeds and iframes without dimensions
  • Dynamically injected content
  • Web fonts causing FOIT/FOUT
  • Actions waiting for a network response before updating DOM

A June 2021 update of CLS now considers long-lived pages as well as pages that are open for a long time.

CLS image  

Where to find the Core Web Vitals report

Core Web Vitals can be measured using any of the tools listed below. Some of these above tools use field data (actual user data) whereas others use user simulation data to predict behaviour patterns.

How to optimise for Core Web Vitals

Google considers Core Web Vitals a key search engine ranking factor. It has a direct impact on your SEO.

It's important when implementing your content strategy to not only optimise your content for keywords, intent and authority etc., but to also consider the overall user experience. .

In an increasingly competitive digital space, you need to deliver a technically sound and balanced digital experience to your website visitors.

A bug free, lag free page experience that doesn't disrupt the user journey can dramatically increase engagement and conversions. The best way to do this is to improve Core Web Vitals by:

  • Optimising and compressing videos and images
  • Implementing lazy loading
  • Optimising for mobile
  • Reducing JavaScript (JS) execution
  • Providing better dimensions for images and embeds
  • Improving server response time

Working with Codehouse

Our Google certified team has helped many customers improve the page experience. To find out more about how our Analytics service can help with your website's performance, or if you need guidance on getting the best out of Google Analytics, get in touch. 

Source of images: Google Analytics

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