Incorporating Lighthouse Performance Metrics Into Selenium Automation

Website performance optimization is imperative in the present era of the digital age, where users expect a very fast loading speed and seamless working of the websites. Slow or poorly performing websites result in poor user experience, high bounce rates and loss of trust in your brand. It is, therefore, the reason to improve the website’s performance, not a best practice but necessary.

Next comes Lighthouse performance metrics, great indicators of your website’s quality. It is evident in its robustness as a tool developed by Google called Lighthouse, which can be used to assess multiple aspects such as loading speed, interactivity, and visual stability of your website. These metrics penetrate beyond the surface and plunge deep down the user experience to provide the developers, as well as the business owners, with vital insights.

However, Selenium automation is a popularly used testing tool and web browser automation framework. It is a useful tool for testing a website by allowing the testers and the developers to simulate different user interactions with the site in order to make sure that the web application works well. What if you could merge the power of selenium automation with the accuracy of lighthouse performance metrics?

This blog will teach you how to integrate Lighthouse performance metrics into your Selenium automation workflow.

Understanding Lighthouse Performance Metrics

Lighthouse is a reliable compass for optimizing website performance. However, before we delve into the issue of Lighthouse and its place in web performance testing, let us first ask – what is Lighthouse? So, let’s go deeper into the Lighthouse’s soul and unravel its mission.

Web Performance Testing Using Lighthouse.

Lighthouse is a multi-purpose instrument built by Google that acts as an indicator of how good a website is. It is not just a tool but your window that showcases how the user perceives the functionality of your site. Lighthouse takes into account multiple aspects of your website, thus providing an overall picture of your page’s performance, accessibility, SEO techniques, best practices, usability and more.

Key Lighthouse Metrics

Lighthouse’s magic lies in its ability to quantify web performance through a set of key metrics:

  1. First Contentful Paint (FCP): At this point, the user sees any content for the first time – it’s FCP. It means your site is functioning and ‘loading’ for the first time.
  2. Largest Contentful Paint (LCP): LCP is the metric of the biggest visual component. It is a vital signal for perceived loading time.
  3. Cumulative Layout Shift (CLS): Your webpage’s stability is measured in terms of CLS. The second measure assesses how much of the content moves when loading is in progress.
  4. Time to Interactive (TTI): When a person enters the scene, TTI warns you. It is exactly that moment when users are able to act on your site by pressing buttons or getting involved in some other way.
  5. Total Blocking Time (TBT): For example, the TBT shows the period of the user blocking while your page is being executed in JavaScript. The reduction of TBT brings about a quick user experience.

Impact on UX and SEO

The Lighthouse metrics are not only numerals but actually influence user experience and SEO. A swift-loading website gives users an enjoyable experience, thereby keeping them engaged on the page. On the other hand, low-speed and content-shifted pages with poor interactivity cause high bounce rates and loss of potential revenues.

In regard to SEO, Google includes page speed and user experience among ranking factors. Websites with high Lighthouse metrics tend to get better positions in Google’s ranking and thus have more organic traffic.

Setting Up Selenium Automation

In order to understand the integration of Lighthouse with Selenium automation, let us first set up the Selenium framework and get conversant in its basics. Here, we will take you through the first steps in automated web testing using Selenium.

About Selenium in Automated Testing.

Selenium is an exceedingly powerful framework and has essentially become the basis of all automated web testing. It enables testers and developers to automate interaction between web applications and different browsers/ platforms. Likewise, selenium offers the flexibility that makes it indispensable in testing the functionality, performance, and reliability of web applications.

Prerequisites for Using Selenium

First, we have to organize our environment before we can exploit the benefits of selenium. Here are the key prerequisites:

  • Installing Selenium WebDriver: Selenium comes with a core WebDriver component that facilitates interaction between your scripts and web browsers. You can install the WebDriver for the browser of your liking, which could be any of the following: Chrome, Firefox, or Safari, based on your preferred programming language.
  • Configuring a Browser Driver: For automating web interactions, you will require specific browser drivers such as ChromeDriver or GeckoDriver (for Firefox). The drivers are intermediaries that help in passing instructions from the Selenium script to the browser. For this, you’ll have to save the right driver and include its path into your path.

A Practical Selenium Script Sample.

As an example of Selenium automation, let’s take something very simple. In this script, we’ll use Selenium to open a web page and interact with it:

# Import the Selenium WebDriver
from selenium import webdriver
# Initialize the WebDriver (in this case, using Chrome)
driver = webdriver.Chrome()
# Navigate to a webpage
# Find an element (e.g., a search bar) and interact with it
search_box = driver.find_element_by_name("q")
search_box.send_keys("Selenium automation")
# Submit the form
# Capture the page title
page_title = driver.title
print("Page Title:", page_title)
# Close the browser

Integrating Lighthouse with Selenium

Having set the scene for automation with Selenium, let us now turn up the heat on web testing even further by incorporating Lighthouse performance measurements. This potent pairing brings along many advantages in terms of accuracy and quality.

Advantages of Merging Lighthouse and Selenium Automation.

The synergy between Lighthouse and Selenium automation brings several advantages:

  • Comprehensive Performance Insights: Aside from Selenium’s functional testing, Lighthouse offers comprehensive metrics providing a glimpse of web performance and user experience.
  • Data-Driven Optimization: Automation of Lighthouse tests will allow the gathering of data from within the app and enable data-driven decision-making in performance improvements.
  • Real User Experience Simulation: The lighthouse metrics indicate how real users perceive your website and, therefore, make your testing methodology user-centered.
  • Early Issue Detection: By integrating at various stages of development, you can detect problems early enough, preventing waste of resources and time. Why stop there, though?

Get Started with LambdaTest for Cross-Browser Testing.

By integrating LambdaTest with Selenium and Lighthouse, you can expect tremendous improvements in your overall testing and performance optimization strategies. LambdaTest is an AI-powered test orchestration and test execution platform used as a solution for browser testing. Using LambdaTest for executing your automatic tests on real browsers provides an opportunity to see how your website works on many different browser platforms. It is significant, especially given that different browsers can provide radically different user experiences. With LambdaTest’s cloud infrastructure, you can execute test scripts simultaneously, thus saving time and energy.

Integrating Lighthouse into Selenium Automation

  1. Installing Lighthouse CLI (Command Line Interface):

– Install Lighthouse globally using npm (Node Package Manager) with the following command:


 npm install -g lighthouse

  1. Using Lighthouse as a Node.js Module:

– Alternatively, you can use Lighthouse programmatically in your Node.js project by installing it as a dependency:


 npm install lighthouse


– Incorporate Lighthouse into your Selenium script using Node.js, allowing seamless integration between performance testing and functional testing.

Running Lighthouse Tests with Selenium

Here’s an example of how you can integrate Lighthouse with Selenium in a Node.js script:


const { Builder, By, until } = require('selenium-webdriver');

const lighthouse = require('lighthouse');

const chromeLauncher = require('chrome-launcher');

(async () => {

 // Launch Chrome browser using Selenium WebDriver

 const chrome = await chromeLauncher.launch({ chromeFlags: ['--headless'] });

 const { port } = chrome;

 // Set up Lighthouse options

 const lighthouseOptions = {


 output: 'json',


 // Initialize Selenium WebDriver

 const driver = await new Builder().forBrowser('chrome').build();

 try {

 // Navigate to a webpage using Selenium

 await driver.get('');

 // Run Lighthouse audit on the current page

 const lighthouseResult = await lighthouse(driver.getCurrentUrl(), lighthouseOptions);

 // Access Lighthouse performance metrics

 const performanceMetrics = lighthouseResult.lhr.audits.metrics.details.items[0];

 // Print Lighthouse metrics

 console.log('Lighthouse Performance Metrics:');

 console.log('First Contentful Paint:', performanceMetrics.firstContentfulPaint);

 console.log('Largest Contentful Paint:', performanceMetrics.largestContentfulPaint);

 console.log('Cumulative Layout Shift:', performanceMetrics.cumulativeLayoutShift);

 console.log('Time to Interactive:', performanceMetrics.interactive);

 console.log('Total Blocking Time:', performanceMetrics.totalBlockingTime);

 } finally {

 // Close the browser and stop Lighthouse

 await driver.quit();

 await chrome.kill();




To test this, we use Selenium WebDriver to go to a webpage, and then we execute Lighthouse on it. The audit results, however, are used to get valuable insights, which are then extracted for lighthouse metrics. This integration indicates the smoothness by which Selenium and Lighthouse can be used in harmony, hence improving your testing strategy.

Capturing Lighthouse Performance Metrics

Once you have successfully integrated Lighthouse with Selenium, it is important to capture and interpret Lighthouse performance metrics meaningfully. Below is a step-by-step guide on how to extract, understand and put them into practice when they become available.

Analyzing test results into Lighthouse metrics.

After a Lighthouse audit on Selenium automation, get the metrics from the Lighthouse report. The audit result can be taken in JSON format that can be parsed to get specific performance metrics programmatically.

Lighthouse Reports in JSON Format

Lighthouse also provides very detailed reports in JSON format, so it is easy to extract any required metric. These are reports containing a lot of useful data, comprising scores and metric values specific to each individual. Here’s a brief overview of the structure:



 "lhr": {

 "requestedUrl": "",

 "finalUrl": "",

 "categories": {

 "performance": {

 "score": 0.92


 // Other categories (e.g., accessibility, best practices, SEO)


 "audits": {

 "first-contentful-paint": {

 "score": 0.94,

 // More data related to FCP


 "largest-contentful-paint": {

 "score": 0.85,

 // More data related to LCP


 // Other audits for various metrics





As in this example, the report contains some categories (e.g. performance, accessibility) and separate audits for every metric (e.g. first-contentful-paint, largest-contentful-paint). Under “score”, there are categories and metrics that correspond with a specific score.

Selenium to Parse and Interpret Lighthouse Reports.

Here’s a sample code snippet to demonstrate how to parse and interpret Lighthouse reports within your Selenium script:


const lighthouse = require('lighthouse');

const chromeLauncher = require('chrome-launcher');

(async () => {

 // Launch Chrome browser using Selenium WebDriver

 // ... (Selenium setup code)

 try {

 // Navigate to a webpage using Selenium

 // ... (Selenium navigation code)

 // Run Lighthouse audit on the current page

 const lighthouseResult = await lighthouse(driver.getCurrentUrl(), lighthouseOptions);

 // Access Lighthouse performance metrics from the report

 const performanceMetrics = lighthouseResult.lhr.audits.metrics.details.items[0];

 // Extract and interpret specific metrics

 const firstContentfulPaint = performanceMetrics.firstContentfulPaint;

 const largestContentfulPaint = performanceMetrics.largestContentfulPaint;

 const cumulativeLayoutShift = performanceMetrics.cumulativeLayoutShift;

 const timeToInteractive = performanceMetrics.interactive;

 const totalBlockingTime = performanceMetrics.totalBlockingTime;

 // Use these metrics for analysis or reporting

 console.log('First Contentful Paint:', firstContentfulPaint);

 console.log('Largest Contentful Paint:', largestContentfulPaint);

 console.log('Cumulative Layout Shift:', cumulativeLayoutShift);

 console.log('Time to Interactive:', timeToInteractive);

 console.log('Total Blocking Time:', totalBlockingTime);

 } finally {

 // Close the browser and stop Lighthouse

 // ... (Selenium cleanup code)




Here we go and execute Lighthouse, then go and read out of a Lighthouse report some specific performance metrics. The metrics collected during your Selenium tests can be used for data analysis and reporting or for making performance optimization decisions.


With this knowledge in hand, the reader is ready to improve their web testing strategy. You can automate not just the operational aspects but also the performance evaluation for your Web-based applications. With Lighthouse metrics, you can base your data-driven decisions on boosting website speed, interactivity, visual stability, rankings of search engines and user satisfaction.

Incorporating Lighthouse Performance Metrics Into Selenium Automation was last updated October 18th, 2023 by Tanveer