Google Lighthouse: Everything You Need To Know

Google Lighthouse is one of our go-to tools for analysing website performance. Although we use the platform daily, we can appreciate that Lighthouse is still relatively new for people working in and out of the industry.

So, we’ve put together this blog post to tell you more about it, how its scoring system works, and most importantly how to use the data and insights to improve your website performance.

What is Google Lighthouse and why is it so useful?

Google describes Lighthouse as an open-source, automated tool that helps to improve the quality of web pages. The audit system features various criteria and is quantified into an overall score across five key categories: performance, accessibility, progressive web apps, best practices and SEO.

Improving these scores brings many benefits for a website owner; it’s worth remembering that Google has picked out the key metrics that they believe are fundamental to website performance. In other words, if Google thinks it’s important, it’s safe to assume that these metrics will impact your search rankings and user experience.

How to use Lighthouse

One of the best things about Lighthouse is how easy it is to use. Although the powerful tool offers detailed analysis, you don’t have to be a web dev expert or a coding genius to run an audit of your website.

• Directly from Chrome DevTools or as a Chrome extension.
• As a Node package.
• From the PageSpeed Insights website.
• Through the web.dev/measure web page.
• Popular website analytics tools such as GTmetrix have updated their algorithms to support Lighthouse.

Once you’ve picked your favourite method you can enter (or copy and paste) the URL of the page that you want to analyse. Lighthouse will then audit the chosen page and compile reports highlighting the key areas for improvement.

We’ll apologise in advance as from this point onwards we start to delve into the technical details about Lighthouse - (cue the heavy use of acronyms and buzzwords). If you come across anything you’re unsure about, drop us a line and we’ll be happy to discuss it in more detail.

Metrics used by Lighthouse

As mentioned above, Lighthouse uses a wide range of metrics that determine performance, accessibility, progressive web apps, best practices and SEO scores.

Here’s a sample of the most useful metrics in the performance and SEO categories:

Performance metrics

• First Contentful Paint - Is commonly referred to as FCP and measures the amount of time it takes for the browser to render the first Document Object Model (DOM) content on the page.
  DOM content includes images, SVGs and non-white canvas elements. Lighthouse displays FCP in seconds.
  
• Speed Index - Is also measured in seconds and this score is used to evaluate how quickly content is visually displayed during page load.
  
• Cumulative Layout Shift - Is often abbreviated to CLS and measures the number of layout shifts that occur during a full page load.

SEO checks

In addition to website performance, you can also use Lighthouse to complete basic SEO checks. Lighthouse is effective for assessing the following SEO criteria:

• Is the web page mobile friendly?
• Does the page have a meta description?
• Is the page blocked from indexing?
• Do the images have alt attributes?

Whilst Lighthouse doesn’t offer comprehensive SEO analysis, the tool will still make you aware of any SEO problems that need to be fixed. Check out this handy blog post to learn more about SEO.

Making sense of the Lighthouse report

Like most analytical tools, Lighthouse provides a detailed report which can be overwhelming if you’re not entirely sure on what you’re supposed to be looking for.

Thankfully, Google’s Core Web Vitals announcement has helped to point us in the right direction. Google revealed that page speed and experience will be used to determine search rankings. With this in mind, we recommend that your first priority should be to ensure your content loads as fast as possible, across all web pages.

Ready to try Lighthouse?

Lighthouse isn’t an all-encompassing tool for measuring website performance. Instead, it should be viewed as a valuable addition to your toolkit. And used in tandem with other analytical platforms like PageSpeed Insights and GT Metrix.

Are you ready to try Lighthouse and improve your website performance, speed and usability? Get in touch to request a free, no-obligation audit from our expert team.