What are Core Web Vitals and why do they matter?


What are Core Web Vitals and why do they matter?

Catena Media currently maintains hundreds of brands globally and publishes 1,000s of new pages every month. Most of our readers find our content through organic search results, so SEO is a fundamental component of our business. 

Producing content that people think is relevant and valuable will always be the driving force behind our content strategy, but the quality of user experience, particularly on mobile, and how that matters to search engines, is an increasingly important factor. Our content must be usable, and the success of our clients’ acquisition strategies, and therefore our own success as a lead generator, depends on it.  

But tracking key performance indicators is nothing new in the content marketing world. On the face of it, measuring factors like page speed is simple. But because search engines keep the make-up of algorithms and the detail around periodic changes close to their chests, there is still a degree of guesswork, trial and error.  

So when Google releases new guidance or tools, it pays to take notice. Enter Core Web Vitals (CWV), a set of metrics introduced by Google in 2021 to assist website owners in improving user experience. 

At Catena Media, we have always asked the question ‘what makes for a bad user experience?’, but with CWV, Google has given us their latest answer. With over 5 million visitors to our brands every month, these insights could have a significant impact on our performance. 

What are Core Web Vitals?

The ultimate goal for any search engine is to highlight content that is well-matched to a search query, which is why Google has historically favoured high quality, relevant content for its users. But as its algorithm and the internet evolve, Google has begun to fold more user experience metrics into the mix. Many publishers still view these as a tiresome box-ticking exercise – just ‘web hygiene’ – but use them right and Google’s guidance is an opportunity to boost your performance and gain ground on your rivals. 


So what does Google now think is ‘vital’?

High speed internet and 4G/5G have finally given us the infrastructure we need, so the onus is on publishers to provide a fast, stable user experience. Page load times have always been an easy target, but now unstable layouts, delays in loading on-screen elements and delays in site response are the latest culprits.

Core Web Vitals are a set of specific factors that Google considers important in a webpage’s overall user experience. These metrics are made up of three specific page speed and user interaction measurements: First Input Delay, Cumulative Layout Shift and Largest Contentful Paint.


Largest Contentful Paint (LCP) measures perceived load speed and marks the point in the page load timeline when the page’s main content has likely loaded. This means LCP measures the time from when a page begins loading to when its largest text block or image element is displayed on the screen. We know that users have little patience for long load times, and that for every additional second, we lose thousands of prospective leads. Sub-optimal LCP scores can be caused not just by heavy files, but also CCS and server-side factors, so diagnosis isn’t just about careful selection of your largest page element. The lower the LCP, the better, with 2.5 seconds a good benchmark to aim for.


First Input Delay (FID) measures responsiveness and quantifies the experience users feel when trying to first interact with the page. This means that FID measures the time it takes for a user to get the ability to interact with the page, such as clicking an option from the navigation bar or checking a checkbox. Interestingly, Google themselves appear to be reacting to the fact that FID is virtually obsolete (as most web platforms now score highly for FID) by developing a new responsiveness metric which judges latency across a group of user interactions, not just the first, and over a longer time period. This is a good example of how CWV should be seen as a moving target, rather than a one-shot silver bullet.

Cumulative Layout Shift (CLS) measures visual stability and quantifies the amount of unexpected layout shift of visible page content. In other words, how the various elements on the page move around in the viewport as the page finishes loading. Poor CLS is distracting for your users, and can be caused by images or elements such as ads or iframes that lack proper dimensions. Because CLS is about distance of shift and impact on other elements of your content, it is not measured in seconds like the other CWV metrics. A score of 0.1 or less is considered good. 


Core Web Vital Factor

Core Web Vitals metrics.

So in essence, Core Web Vitals are a set of user-centric performance metrics related to speed, responsiveness, and visual stability that help you measure the level of UX your website renders. Although Google has raised the profile of CWV this year, other core metrics are still important in the fight for better user experience:

Mobile friendly;  Compatible plugins, defined viewport properties, use of a responsive viewport that matches device-width, size content to that viewport & size clickable elements appropriately.

Safe Browsing; Sites that do not use Malware, deceptive pages, harmful downloads, uncommon downloads, deceptive sites & unwanted software.

HTTPSUses encryption, data integrity & authentication. 

No Intrusive Interstitials - (Pop Ups); Covering most or all of the content of a page, difficult to close & popping up without prompt (some pop ups are a requirement - i.e. cookie policy).

You’d think that, with so much guidance to leverage, businesses would be ahead of the curve. But according to one study, around half of the 100 most visible websites on Google are still failing Core Web Vitals assessments. There are many reasons for this, but it’s good news for publishers who are already investing in user experience.  


Knowing what benchmarks to aim for is one piece of the puzzle. But what tools should you use? Can you predict how a page will perform before it’s out in the wild? And what happens when you have conflicting data? In part 2 of this series on Core Web Vitals, we will look at lab data versus field data and explain why both matter in the quest for content that keeps users and search engines happy.