How to Use Google Lighthouse for Testing Website Performance

Follow the light that propels your website into the fast lane!

When it comes to ranking your website higher in search engine results, website speed is a factor that cannot be ignored. Not only does it delight users, but also translates into increased visibility. After all, nobody wants to click on a page and wait forever for it to load. You see TechCult for example, our blogs load pretty fast, doesn’t it? Hah, jokes aside, If you’re worried that your website isn’t able to rank because of low speed, Google Lighthouse is here to help you out. In today’s article, we will show you how to use Google Lighthouse for performance testing.

How to Use Google Lighthouse for Testing Website Performance

What is Google Lighthouse & How to Use It for Performance Testing?

It’s a commonly said proverb that the first impression is the last. On that note, often a website that loads quickly stands tall in terms of better user experience, which can ultimately result in increased conversion rates. Even search engines like Google rank faster-loading websites higher in search results.

Google Lighthouse is an open-source automated tool that helps website developers and owners, evaluate & improve the quality of web pages. It has audits for performance, accessibility, best practices, and SEO for both mobile and desktop. Based on its detailed reports and recommendations, users can optimize the performance of the site for better user engagement. Lighthouse can be run against any web page, publicly or privately accessible. Let’s see how it works and how you can use it.

Method 1: Directly Add and Run Lighthouse

Lighthouse is also available for users in the form of a Google extension, that you can download to run audits for you on Chrome browser. Follow the steps below:

1. Visit the Chrome Web Store page for the Lighthouse extension on any web browser.

2. Click on Add to Chrome.

Click on Add to Chrome for Google Lighthouse

3. Select Add extension to confirm.

4. Once added, launch the website on the browser that you would like to analyze.

5. Click on the Extension (Puzzle) icon next to the address bar and select Lighthouse.

6. Click on Generate report.

Click on Generate report. | lighthouse performance testing

That’s it! In a few seconds, Lighthouse will generate a detailed report analyzing the website you ran the test for.

Method 2: Use PageSpeed Insights

Google PageSpeed Insights is also a web performance testing tool that uses Lighthouse as its analysis engine. You can hence use it to generate reports for your website. Follow the steps:

1. Visit the PageSpeed Insights website.

2. Enter the website URL in the text field and click on Analyse.

Enter the website URL in the text field and click on Analyse.

Once the testing is done, you’ll receive the Chrome User Experience Report that shows results experienced by real users.

PageSpped Insights results | lighthouse performance testing

The Diagnose performance issues section represents the Lighthouse score. You can check results for both Mobile and Desktop.

Lighthouse results - Diagnose performance issues

Method 3: Run Lighthouse in DevTools

Lighthouse has its panel in Google Chrome DevTools that you can also use for testing the performance if your website runs on a local server or also for sites that require login. Here’s how to do it:

1. Visit the website you want to audit.

2. Right-click anywhere on the page and select Inspect from the menu.

Right-click anywhere on the page and select Inspect from the menu. | lighthouse performance testing

3. Click on the >> icon (More tabs) and select Lighthouse from the context menu.

Click on the (More tabs) and select Lighthouse from the context menu.

4. Click on the Analyze page load button at the top-right and wait until the results are ready.

Note: Select the Device appropriately and keep all the Categories enabled. 

Click on the Analyze page load button at the top-right and wait until the results are ready.

You can also change the mode. Lighthouse in DevTools provides three testing modes:

  • Navigation: Displays overall results including Performance, Accessibility, and SEO.

Navigation results Lighthouse in DevTools | lighthouse performance testing

  • Timespan: Shows results based on how long a page takes to load and interact with the surfer. You would need to interact with the page while the test is running.

Timespan Lightshouse Score DevTools

  • Snapshot: Computes score for the current page

Snapshot Lighthouse score DevTools | lighthouse performance testing

Also Read: 31 Best Web Scraping Tools

Method 4: Use Lighthouse Module with Command Line

 Lighthouse is also available as a Node module that you can integrate into your continuous integration systems and use as a command line or programmatically. All it requires is a version of the node. If you have Node.js installed on the PC, follow the steps below:

1. Login to your server and run the following command to install the Lighthouse global module on the device:

npm install -g lighthouse

2. Once installed, run the following command to perform a Lighthouse test:

lighthouse -- view <url>

You can view all the available options using the following command.

lighthouse --help

How Does Lighthouse Calculate Score

Google Lighthouse combines and evaluates various aspects of a website’s performance metrics, such as Performance, Accessibility, Best Practices, SEO, and PWA. Once the audit is successful, it then generates a report that includes a score for each aspect, as well as recommendations for necessary improvements to improve the performance and user interaction of your website. Websites are typically rated on a scale of 0 to 100. 

Performance

Lighthouse analyzes how quickly a web page loads. The performance score is calculated by taking into account the following metrics –

  • First Contentful Paint (FCP): How quickly the first element from the content is painted on the screen
  • Largest Contentful Paint (LCP): Measures the time it takes for the largest content element to become visible
  • Cumulative Layout Shift (CLS): Measures the amount of unexpected layout shifts that occur during the page load to assess the visual stability of the page. Low CLS indicates that the website is stable. 
  • Total Blocking Time: Measures the time during which the main thread is blocked and unresponsive to user input.
  • Speed Index: Indicates how quickly all the content of the page is completely visible

These metrics gauge the website’s loading speed and visual stability. Several factors influence this report, like the size and number of images, the number of plugins used, and the efficiency of the website code.

Performance Score Lighthouse | lighthouse performance testing

Lighthouse calculates the score by taking the weighted average of the metric values. Naturally, measurements with a higher weighting have a greater impact on your total Performance score. The metric scores are not displayed in the report but are calculated behind the scenes. You can click on See calculator option to gain access to the detailed calculation of factors affecting your website.

Lighthouse Scoring Calculator for Performance

Accessibility

It is a user-centric score that measures how easy it is for users with disabilities to access your website. It is influenced by factors such as the presence of alt text on images, the use of ARIA attributes, and the keyboard accessibility of your website. Each accessibility audit is either a pass or a fail. A page does not receive points for partially passing an accessibility audit, unlike the Performance audits.

  • Alt Text for Images: All the images on the page should have appropriate and descriptive alt text, as it is needful for users with visual impairments who rely on screen readers to interpret images.
  • Semantic HTML: Proper use of semantic HTML elements such as the title, headings, lists, etc help screen readers and other assistive software understand the page’s structure
  • Color Contrast: Color Contrast between the text and its background should meet the standards set by Web Content Accessibility Guidelines. Sufficient color contrast ensures that the text is readable for individuals with poor vision or color blindness. 

Accessibility Score Google Lighthouse | lighthouse performance testing

Also Read: How to Build a Website Using ChatGPT

Best Practices

Lighthouse measures how well your website follows web development best practices & coding standards and provides a score based on it. It checks the use of modern JavaScript features and secure connections (HTTPS) and is influenced by factors such as the use of minification and compression, the presence of security headers, and the use of robots.txt files. Some of the common audits under it include:

  • Avoid Large JavaScript Libraries
  • Avoid Unused CSS
  • Enable Text Compression
  • Eliminate Render-blocking Resources
  • Leverage Browser Caching
  • Serve Static Assets with an Efficient Cache Policy

Best Practices Lighthouse Score

SEO

SEO measures how well the website is optimized for search engines. It is influenced by factors such as the presence of meta descriptions and title tags, the use of relevant keywords, and the structure of your website’s content. The score is calculated by averaging the scores for the following audits:

  • Document Title
  • Description
  • Headings
  • Images
  • Links
  • Meta Description
  • Robots.txt

SEO Google Lighthouse Score | lighthouse performance testing

Also Read: 27 Best Free Website Hosting Services

How to Interpret the Results

Lighthouse converts each raw metric value into a metric score of 0 to 100. The higher the score, the better it is. The metrics scores are colored according to these ranges:

  • 0 to 49 (Red Triangle): Poor
  • 50 to 89 (Orange Square): Needs Improvement
  • 90 to 100 (Green Circle): Good

When running it tests on the same website, it’s common to observe fluctuations in the overall scores. This variability can be attributed to several factors.

  • Each analysis only provides insights into the performance of a single page load. Since no two-page loads are identical, load times can naturally differ. 
  • Page speed can be influenced by the presence of dynamic content, such as ads or frequently changing elements, browser extensions that alter network requests and background activities on the PC.
  • Scores obtained in different environments, such as PageSpeed Insights and your local computer, may not be directly comparable due to differences in hardware and network conditions.

How to Improve Your Lighthouse Score

Lighthouse provides both lab data (simulated tests) and field data (real user data) to evaluate a web page’s performance. Field data offers insights into how actual users experience the site, while lab data is useful for testing changes and improvements.

Web designing

Begin by concentrating on the recommendations in the domain of performance. A faster-loading website will improve user experience and may boost your SEO ranking. Once your performance score has improved, you may begin to focus on the recommendations in the other areas. Because accessibility and SEO are essential components in the overall quality of your website, it is worthwhile to devote effort to enhancing these areas as well.

Also Read: Zyro vs Wix: Which Website Builder Should You Choose?

Bonus Tips for Beginners

If you have just designed and launched your website, here are some more pointers you should keep it might:

  • Don’t be overwhelmed by the Lighthouse report’s numerous suggestions. Begin with the most crucial advice and work your way down the list.
  • The Lighthouse report may be used to track your development over time. Your Lighthouse ratings should improve as you execute the recommendations.
  • Remember to test your website on many devices and browsers. Because the Lighthouse report is based on a single test, it is critical to test your website across several devices and browsers to ensure that it is operating well for all users.

We hope our guide helped you understand how to use Google Lighthouse for testing the performance of your website and thereby improving it. If you have any queries or suggestions for us, do let us know in the comments section. Stay tuned to TechCult for more such informative blogs.

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