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Google Lighthouse: What It Is and How to Use It for Better Website Performance

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What Is Google Lighthouse?

Google Lighthouse is a free tool developed by Google that enables you to enhance the quality of webpages on your website.

The software performs an audit on your pages to evaluate their performance, accessibility, SEO, and other aspects, and provides recommendations for improvement.

Google Lighthouse is open-source, meaning that anyone can use it on any webpage.

Whether you are a web developer, SEO specialist, or website owner, Google Lighthouse can help you improve your website’s overall experience and performance.

This article will explain how Google Lighthouse operates and how you can use it to audit your webpages.

Without further ado, let’s get started.

How Does Google Lighthouse Work?

Google Lighthouse functions by conducting evaluations across five key categories of website optimization.

1. Performance

During its audit, Google Lighthouse assesses website speed and accessibility, evaluating how quickly users can access the website and its contents.

The tool reports on six speed metrics, each measuring a different aspect of page speed:

Six metrics tracked in the Performance section of the Lighthouse report
  • First Contentful Paint (FCP): Measures the time at which the first text or image becomes visible to users.
  • Largest Contentful Paint (LCP): Calculates the time a page takes to load its largest element for users.
  • Total Blocking Time (TBT): Measures the amount of time that a page is blocked from reacting to user input, like a mouse click.
  • Cumulative Layout Shift (CLS): Measures the layout shifts that occur as users access a page.
  • Speed Index (SI): Shows how quickly the content of a page is loaded.
  • Time to Interactive (TTI): Measures how long it takes a page to become fully interactive.

Lighthouse calculates an overall performance score for a page based on its performance across these metrics. The score ranges from 0 to 100.

A score between 90 and 100 indicates that the page is optimized for a positive user experience. Anything below 90 suggests that a significant number of resources on the page are slowing it down, negatively affecting the overall experience.

Lighthouse also provides suggestions for improving page performance.

2. Accessibility

The accessibility test of Google Lighthouse evaluates the usability of your website for users who rely on assistive technologies.

It examines elements like buttons and links to determine if they are well-described, and analyses images to see if alt text has been specified. This ensures that users with limited or no vision who use screen readers can comprehend the image’s content.

Like the performance audit report, the accessibility report provides a score out of 100, with a higher score indicating better accessibility.

The accessibility test of Google Lighthouse.

The tool also identifies potential areas for improving the website’s overall accessibility.

3. Best Practices

The best practices audit within Google Lighthouse evaluates whether your webpage conforms to modern web development standards.

Lighthouse examines various aspects of your page, including:

  • Whether resources load from secure servers with HTTPS.
  • If images display with the correct aspect ratio and resolution.
  • Whether JavaScript libraries are secure and free of vulnerabilities.
  • Whether the page has the HTML doctype.
  • If the Content Security Policy (CSP) effectively guards against cross-site scripting (XSS) attacks.
  • Whether the page is free of browser errors and deprecated frameworks and APIs.
  • If the page has valid source maps.
  • Whether the page is free of issues appearing in the Chrome DevTools panel, such as network request failures, insufficient security measures, and other browser issues.
  • Whether the page’s character encoding is set with the meta charset tag.
  • If the page allows users to paste passwords in the password field.
  • If the page blocks geolocation and notification permission requests on page load to create a better user experience.

Lighthouse generates a score out of 100 based on all these factors.

The report also highlights specific elements that require attention and can improve the overall score.

4. SEO

Google Lighthouse includes an SEO audit that examines various technical aspects of your webpage.

The tool checks whether:

  • Your webpage is mobile-friendly.
  • The page has valid structured data.
  • Internal links are crawlable.
  • The page has a valid hreflang attribute.
  • Title and meta description tags are set.
  • The page is indexable.
  • Robots.txt is valid.
  • The page is returning an HTTP 200 (OK) status response code.
  • The page has a valid “rel=canonical” tag set.
  • Page content is independent of plugins.
  • Links on the page are introduced with descriptive text.
  • Images on the page have image alt texts specified.
  • The page has a viewport meta tag with width or initial-scale set.

Lighthouse generates a score out of 100 based on all these factors and also highlights any SEO issues detected during the audit.

5. PWA (Progressive Web App)

Lighthouse’s PWA audit examines whether your web application is designed to provide an optimal user experience using modern web capabilities.

It verifies if your web app:

  • Offers a reliable and fast experience on mobile networks with offline functionality.
  • Can be installed on multiple device types and has features like push notifications and offline functionality.
  • Optimized for PWA by configuring a custom splash screen, redirecting HTTP traffic to HTTPS, resizing webpage content to fit on mobile screens, and implementing all other Lighthouse’s best practices.

After running the test, Lighthouse assigns one of the PWA badges to your web app.

PWA badges to your web app

Unlike the first four reports, the PWA audit report doesn’t assign a score out of 100, instead, you’ll receive a badge.

The report also includes suggestions for improving your overall PWA performance, including specific issues that require your attention.

How to Use Google Lighthouse

Now that you’re familiar with Google Lighthouse and how it functions, it’s time to explore the various ways you can utilize it to audit your website pages.

Using Lighthouse with Chrome Extension

You can use the Lighthouse Chrome extension to perform audits on your webpages.

  • First, install the Lighthouse Chrome extension on your browser.
  • Next, visit the webpage you want to test.
  • Then, open the Chrome extension menu and choose “Lighthouse.”
  • Click the cog icon to access the settings where you can select or deselect specific categories based on the reports you want to generate.
  • Finally, click the “Generate report” button to start the audit.
  • Lighthouse will generate a report for you in a new tab.

Using Lighthouse with Chrome DevTools

To run a Google Lighthouse audit with Chrome DevTools on your Chrome browser, follow these steps:

  • Open the webpage you want to audit.
  • Right-click anywhere on the page and select “Inspect.”
  • The Inspect feature will open a DevTools panel on the right side of the webpage.
  • Select “Lighthouse” from the panel’s toolbar. If you can’t find the Lighthouse option, click on the two arrows at the end of the toolbar, and you’ll find it there.
  • Choose one or more categories or select all categories based on which aspects of your website you want to analyze. Click “Analyze page load.”
  • The tool will generate a report for you. You’ll find your audit scores for each category at the top.
  • Click on a specific category to learn more. For instance, if you want to learn more about the “Performance” audit, click on it.

Using Lighthouse in PageSpeed Insights

You can also access Lighthouse through Google’s PageSpeed Insights tool.

To get started, open the tool and enter the URL of the page you want to analyze. Then click on the “Analyze” button.

Using Google Lighthouse via Node Module

To use Lighthouse audits through a Node JavaScript module, you need to follow these steps:

  • Install the latest version of Node.js on your system.
  • Install Lighthouse by running the following command line
npm install -g lighthouse
  • After Lighthouse is installed, use the following command line to generate reports:
lighthouse --output json --output-path

Replace ‘<url-to-audit>‘ with the URL of the webpage you want to audit, and ‘<path-to-save-the-report>‘ with the location where you want to save the report.

FAQs

How Is Lighthouse Different from PageSpeed Insights?

Lighthouse and PageSpeed Insights differ in how they measure the performance of your pages. Lighthouse uses lab data exclusively, while PageSpeed Insights uses a combination of lab and field data.

Lab data is simulated and reflects how hypothetical users may experience your site, while field data is gathered from actual users and reflects how real users experienced your website.

Why Are My Scores Different Each Time I Test?

The scores you receive from Lighthouse may vary each time you perform the audit. This is because factors such as network conditions, browser extensions that modify network requests, and ads displayed on the specific page can influence the results.

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