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Core Web Vitals: Common myths.

March 18th 2021



Last year, Google announced that Core Web Vitals will form part of the Search algorithm starting in May 2021, along with other known page experience signals.

Along with this announcement back in May 2020, Google also stated that they would be rolling out a test to provide a visual indicator in SERPs to highlight pages with a ‘great experience’.

Since this announcement, it’s clear that SEOs, web developers, marketing managers and business owners have become increasingly concerned that their websites aren’t up to scratch. It’s rare for Google to announce algorithm updates so far in advance, so industry experts have predicted that this could be a significant ranking update.

What are Core Web Vitals?

Google themselves describe Core Web Vitals as “a set of metrics related to speed, responsiveness and visual stability, to help site owners measure user experience on the web.”

These metrics are calculated based on things like:

  • How fast does a page load?
  • How quickly does it take for the page to be interactive?
  • How long does it take for the web page to be stable?

Essentially, core web vitals focus on the experience visitors have when on a web page from a mobile or desktop device.

The Core Web Vitals themselves are three metrics which are all unique from each other. These are as follows:

Largest Contentful Paint (LCP)

The time interval between the start of a page load to when the largest image or text block in a user’s viewport is fully rendered. Please note that this is different from ‘first contentful paint’, a metric which focuses on the first element that’s loaded rather than the biggest one.

First Input Delay (FID)

This metric measures how long it takes for a page to be ready for user interactivity. FID focuses on the time between clicks, scrolls, or keyboard input and the processing of that interaction. User interaction is often delayed by main thread-blocking script tasks.

Cumulative Layout Shift (CLS)

This final metric measures page stability. CLS is an algorithm which looks at unexpected layout shifts as a page loads. When the dimensions of a hero image are not defined, for instance, text on the page first appears and is then displaced, causing a disruptive content layout “shift” for the user.


This highly anticipated update has caused a lot of chatter in SEO blogs and forums online, meaning there is a lot of confusion around the subject. So, what’s true and what’s not?


Myth #1: There is only one way to measure Core Web Vitals scores.

False. Analysing a wide variety of data sources to measure your Core Web Vitals is super important. A combination of lab data (using website crawlers like DeepCrawl and/or Google’s Page Speed Insights tool), and Chrome User Experience Report data is your best bet.


Myth #2: If Google deems a site as ‘mobile friendly’ it’ll be fine for the CWV update.

False. Google sees mobile-friendliness and Core Web Vitals as two separate search signals. Although there is some crossover, they remain two very different things in the eyes of Google. If a page is mobile-friendly it has been optimised for mobile browsing, but Core Web Vitals goes further than that, looking at whether a page loads quickly and focussing on elements of interactivity and visual stability.


Myth #3: Core Web Vitals will be the most important ranking factor.

False. Unfortunately, Google never has and never will reveal the “most important ranking factor”. Page experience is one of many signals Google uses to rank pages.

Matching the user intent is still a very strong signal; the quality and relevancy of your content will help you rank well in organic search. Google themselves say: “a page with a subpar page experience may still rank highly if it has great, relevant content.”


Myth #4: If a page loads quickly on one device, it will be fine on all devices.

False. Many factors impact how a page will load on different users’ devices. Network connections, geography and device type may contribute to how fast a page loads for a particular user. Unfortunately, if one user has a great experience on your site, this may not be indicative of another user’s experience. Google’s Core Web Vitals look at the full body of user visits and its thresholds are assessed at the 75th percentile across the body of users.

Google states:

“Depending on how you’re evaluating ‘Fast’, remember that Core Web Vitals is looking at more than speed. For instance, Cumulative Layout Shift describes users annoyances like content moving around. Additionally, you may also use synthetic-based testing tools that try to emulate a user, but that representation may differ from your real users.”


Myth #5: If my site is scoring well for ⅔ of the metrics, there’s no need to worry.

False. Last month, it came out that all Core Web Vitals may need to be met for a site to receive a ranking boost. Although this one hasn’t been 100% confirmed, it seems that the general consensus is that a site should be scoring fairly well in all three areas to be ‘off the hook’ in May. John Mueller, a leading Search Advocate at Google has said that:

“There are a number of factors that come together and I think the general idea is if we can recognize that a page matches all of these criteria then we would like to use that appropriately in search ranking.”

See the full discussion in the video below:

This is a typical elusive response from Google, but we would recommend a site in the ‘Green’ zone on tools which measure CWV wherever possible.

We hope this helps you to ignore all the ‘noise’ and prepare your site for the search algorithm update in May. If you have any questions, please do not hesitate to get in touch.

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