What they are and how to optimize for SEO

Core web vitals are performance indicators related to three key aspects of the user experience: page loading speed, interactivity, and visual stability.

Announced a year ago, Google’s core web vitals have been significant ranking factors since May 2021 for website owners, as they impact organic placement in the SERP.

This means that if pages offer a faster, more interactive, and stable browsing experience, they have a greater chance of appearing high in search results.

If you’ve wondered how to rank first in search engines, delving into the content of this article will be helpful.

Here, you can understand the functioning of core web vitals, monitor them, and optimize them through tests to enhance user experience as a ranking factor.

If you want to rank high in organic search and expand your skills in the field, you can take advantage of the SEO Specialist Course and User Experience Course, where you can learn the secrets of Search Engine Optimization.

Guide to google web vitals

What are the essential signals for Google? This phrase literally translates the term core web vitals, which, as mentioned, are fundamental metrics for navigation quality and SEO.

Indeed, the introduction of Google web vitals rewards sites with good User Experience to ensure the user a smooth, fast, and responsive browsing experience, leaving them satisfied.

This standardized way of evaluating these aspects is based not only on statistics but also on real data related to user behavior.

This has led to a merger between SEO and UX, completing a cycle of updates initiated long ago by the search engine giant.

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Certainly, UX will never be more important than content, but its quality will reward resources competing for the same search query.

In other words, these new metrics will influence the SEO positioning of organic content searches.

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Core web vitals: 3 ranking factors useful for UX

Having understood, in general, what Core Web Vitals are for, it is necessary to delve into how they are useful for the qualitative measurement of pages and ranking evaluation.

Let’s take a step back. Every time Google launches essential updates, they identify them as core updates.

The web vitals, in detail, are the three metrics related to page loading speed, response time, and the stability of the web page layout.

So, what are the Core Web Vitals?

  1. LCP (Largest Contentful Paint) is related to loading speed.
  2. FID (First Input Delay) is related to page interactivity.
  3. CLS (Cumulative Layout Shift) is related to the visual stability of the site’s objects.

core web vitals metrics

LCP: Largest Contentful Paint

This parameter refers to the speed of loading the largest element visible to the user, assuming that this is also the most important content.

Consequently, intrusive elements, such as large titles and opening images, pop-ups, and the like, will be penalized.

In particular, the essential web signal LCP analyzes these elements:

  • File <img>;
  • Images of type <svg>;
  • File <video>;
  • CSS-loaded background images;
  • Text blocks within content.
lcp essential web signal


As you can see from the image above, in both situations, the largest element changes while the content is loading.

Google indicates that to provide a good UX and easy access to content, the Largest Contentful Paint (LCP) metric should be kept within 2.5 seconds.

Beyond this value, pages require optimization: if they exceed 4 seconds above the fold, i.e., in the top part of the website visible to the user without scrolling actions, the system is considered too slow.

essential web signal lcp


FID: First Input Delay

The FID is the core web vital according to Google, corresponding to the delay of the first interactivity, such as clicking on a link or touching on mobile.

It measures the time it takes for the browser to respond to that interactivity. It is the first input delay that determines the perception of site responsiveness.

Furthermore, Google has observed that the biggest interactivity issues occur during the page loading phase.

Consequently, the search engine giant suggests that improving users’ first interaction response times has a positive impact on the overall user experience.

first input delay


Typically, the main interactivity issues with the site occur during the loading of the first page, either because it happens in multiple stages or because JavaScript is loaded too early.

With a good browsing experience, users should interact with the page within the first 100 milliseconds (green zone).

Pages with FID over 100 milliseconds require optimization (yellow zone), while those exceeding 300 milliseconds are considered poor (red zone).


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CLS: Cumulative Layout Shift

CLS measures the visual stability of loading, specifically the changes in layout during the loading of page elements. You’ve likely encountered pages where elements load asynchronously.

This leads to sudden and unexpected changes in the page structure. For example, as you read an article, it might shift downward due to the loading of an image, or the link you intended to click on moves, making room for a banner.

These unexpected movements worsen the site’s usability and can create concrete issues for the user, leading them to leave the page. Among the Google web vitals, CLS tests the functionality of mixed content on sites.

The causes can vary images or videos with unset dimensions, fonts that load slowly and whose final sizes don’t match the default font, and third-party elements that behave differently in production than in development.

The CLS web signal assigns a score to each abnormal layout shift if it causes unexpected movements of text, images, or boxes.

Calculating this metric is perhaps the most complex among the core vitals. The formula for the layout shift score is impacted fraction * distance fraction.

  • The impact fraction, or impact space, is the sum of the space occupied by the unstable element before and after the shift, calculated as a percentage of the visible screen.
  • The distance fraction is determined by the length of the maximum movement made by the mobile element, divided by the larger dimension of the window.
cls web signal


The score results from multiplying these two factors. The hypothetical optimal value should be below 0.1 (green), from 0.1 to 0.25 needs optimization, while any value above 0.25 indicates a negative UX.

Core web vitals test

Web Core Vitals allow measuring the browsing experience, but how to assess the quality of a website?

Over the years, Google has provided various tools to perform website analysis to improve its usability and provide clear and quick responses to users.

Currently, several tools are available to measure site performance and obtain a web report, including:

  • Google Search Console analyzes all pages of a site and organizes them for results, distinguishing between desktop and mobile navigation.
  • Chrome UX Report provides a summary of the site visitor’s experience.
  • Web Vitals Extension allows creating real-time reports on web vitals directly from the page being browsed.
  • Page Speed Insight records navigation speed on mobile and desktop devices, providing data on how users utilize that resource. Unfortunately, this tool works on individual pages and cannot provide an overall view of the site’s performance.
  • Lighthouse provides insights on SEO, accessibility, and UX.
  • Chrome Dev Tools is a set of web developer tools that allow examining HTML and resolving ad publishing issues.

These tools use measurements collected from the Chrome User Experience Report (CrUX), a set of public data and metrics derived from real browsing statistics.

It should be noted, however, that these tools provide data limited to users who have consented to certain conditions, a sample, and not the totality of browsing experiences.

This is why Google encourages site owners and developers to directly collect real data on their core vitals using a dedicated open-source library for Web Core Vitals and JavaScript API, which through Google Tag Manager, will allow transferring metrics to Google Analytics and exporting them to Google Data Studio.

A web analyst is a professional specializing in online data analysis, with the goal of understanding and optimizing the functioning of websites and web applications.

Their work involves collecting, processing, and analyzing data related to visits and user interactions with a website, aiming to identify areas for improvement and suggest solutions to increase conversions and user engagement.

The web analytics specialist uses tools like Google Analytics to collect and analyze data and is knowledgeable about data mining and data visualization techniques to represent them clearly and meaningfully.

Additionally, they must be able to manage A/B testing to evaluate the effectiveness of different design and content solutions.

Learn to analyze the effects of Google Core Web Vitals!


How to improve core web vitals?

After explaining what Core Web Vitals are, you will better understand how measuring and monitoring the key web signals are crucial for having SEO-optimized web pages and providing a good user experience.

Google provides some guidance on how to optimize Core Web Vitals, considering that the algorithm analyzes UX and influences the positioning of various content in the SERP.

  • Optimizing sites for mobile;
  • Structuring lightweight pages to facilitate quick loading;
  • Using the HTTPS security protocol;
  • Structuring ad spaces with interstitials (JavaScript or Flash) to avoid layout loading issues.

good user experience

Google suggests monitoring Core Web Vitals and correcting anything that doesn’t perform optimally. Corrections should include:

  • Page weight below 500 KB;
  • The number of page resources is limited to 50;
  • Use of AMP pages.


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The Google Core Web Vitals updates promote and reward well-structured, reassuring, and user-friendly sites with a good position in the SERP.

Despite this, the importance of content – content is king – is emphasized, confirming the value of the information contained on the page when the site’s navigation meets low-performance standards.

The Google Web Vitals assessment will confirm whether a resource is adequately fast, functional, easy to use, and free of layout errors that could disorient the user and lead them to abandon the page.

It is therefore all these indicators that, when optimized, create positive browsing experiences for users and contribute to improving search engine optimization (SEO).

Underestimating their effects inevitably means being relegated to lower positions in search engines and consequently a drastic reduction in conversions.

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