Google Lightouse: The Web Page Audit Tool

A new Google auditing tool was released on February 5, 2018: the Google Lighthouse Chrome extension. It is an open-source software used by Search Console that allows you to perform a quick SEO audit of your web page and analyze its performance. This free plugin is downloadable on your web browser, and helps you identify the UX elements to be improved on your pages immediately. Read this article to know the features of this SXO tool and understand how it performs.
Google Lightouse

November 4, 2021


Google Lighthouse Features

Google Lighthouse is used to measure and analyze different points. It analyzes several criteria, with a score from 1 to 100, to guide the user on the improvements he can make to his website.

The Google Lighthouse extension is also used to analyze the satisfaction of website users, and the performance of Progressive Web Apps (PWA). Its functionalities therefore allow to improve a website’s SXO, from natural referencing to user experience.

Understanding Google Lighthouse Performance Score

There are 6 key elements to determine Google Lighthouse performance score of a website. Each of these 6 audit criteria has a weight in the score calculation, ranging from 5% to 25%. Let’s take a closer look at these performance criteria.

First Contentful Paint (FCP)

The FCP refers to the time it takes for the browser to display the first content element DOM (Document Object Model, programming interface) when loading a web page. The elements considered as DOM content are images, SVG or vector graphics, “canvas” or elements not blank.

To calculate the FCP score, the FCP time of your web page is compared with the FCP times of real websites from the HTTP archive database. The weight of this audit criterion is 15% in the calculation of the Lighthouse performance score.

Speed Index (SI)

The Speed Index shows the speed at which the visual content of a web page is displayed during its loading. A loading video is captured in the browser to measure the visual progress of the elements. To generate the score for this criterion, Google Lighthouse relies on the Speedline Node.js module.

The SI score is calculated by comparing the speed index of your web page with the speed indices of real websites based on the HTTP archive data. The weight of this audit criterion in the calculation of the Lighthouse score is 15%.

Largest Contentful Paint (LCP)

This criterion provides an indication of how quickly the user can see the content of the web page. It calculates the loading time needed to display the main content.

This completes the first audit criterion: the First Contentful Paint. The LCP is considered “good” by Google if it is below 2.5 seconds. In the Lighthouse score calculation, this criterion has a weight of 25%.

Time To Interactive (TTI)

For an optimal user experience, it is not enough to display the content: you must also measure the time required for the page to be fully interactive. This is what the TTI audit criterion measures.

A web page is considered interactive when it responds to user interactions within 50 milliseconds. The weight of this audit criterion in the Lighthouse score calculation is 15%.

Total Blocking Time (TBT)

The TBT is the total time during which a web page remains blocked when it must respond to the user’s inputs. Such inputs may include keyboard taps or mouse clicks. Tasks are considered “long” after a duration of 50 milliseconds to execute, and it is the time after this delay that will be considered.

The TBT score compares the TBT time of your web page with the TBT times of the top 10,000 sites on mobile devices. This audit criterion has a weight of 25% in the Lighthouse score calculation.

Cumulative Layout Shift (CLS)

The CLS criterion measures unexpected layout shifts that can affect user experience on your website. A layout shift occurs when an element changes position unexpectedly. These content movements are caused, for example, if the resources are not loaded synchronously.

The CLS score is measured when a user wants to click on a link but ends up clicking on another link due to a lag. Its weight in the Lighthouse score calculation is 5%.

How to use Google Lighthouse in the easiest way?

Perform the indicator audit in seconds via the Web UI

With the Google Page Speed Insights tool, you can find out the speed of your website in just a few moments and get recommendations for optimizing it. This web performance tool allows you to quickly identify ways to improve user experience and is based on the Lighthouse API.

All you have to do to use it is entering your site’s URL in the PageSpeed Insights analysis bar and click “Analyze”. The website performance results are then displayed, with an overall score at the top that represents the average of the various factors seen earlier.

Using browser extensions

You can also use the Lighthouse tool by downloading browser extensions. These use the PageSpeed Insights API to generate performance reports directly through your browser.

  • To download Lighthouse on Mozilla Firefox or Tor, click here.
  • To download Lighthouse on Google Chrome, Microsoft Edge or Brave, click here.

How to influence SXO indicators and improve performance?

Lighthouse’s various audit criteria and performance scores allow you to target improvements to optimize user experience.

In the report generated by Google Lighthouse for your website, refer to the “Opportunities” and “Diagnostics” sections: you will find detailed suggestions for actions you can take, as well as insights into what can be worked on and improved.

In the SEO game, Lighthouse is a must-have audit tool to optimize your website’s user experience. Not only is it free, but it also provides valuable information to improve your SEO and SXO performance.