How to Test Your Website Speed With Google Lighthouse

8-minute read
Apr 1, 2024

Elevate website speed with Google Lighthouse! Discover expert tips for top-notch performance!

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In the digital age, where users demand instant access and seamless experiences, your website's speed plays a pivotal role in its success. A swift-loading site enhances user satisfaction and influences its search engine ranking, making it a crucial aspect of effective SEO strategies. In pursuing optimal website performance, Google Lighthouse emerges as a beacon, offering a comprehensive and automated analysis of your web pages.

We internet users have all experienced the frustration of slow-loading websites. Research indicates that users tend to abandon pages that take more than a few seconds to load. Beyond user experience, website speed is a crucial factor search engines consider in determining rankings. Being at the forefront of search engines, Google has introduced tools like Google Lighthouse to empower website owners, developers, and SEO professionals in their quest for speed optimization.

At the heart of this guide lies Google Lighthouse, a versatile and accessible tool developed by Google. This tool goes beyond just evaluating speed; it delves into four critical categories—Performance, Accessibility, Best Practices, and SEO—providing a holistic assessment of your website. Each category contributes to an overall score, offering actionable insights and suggestions for improvement. Moreover, Google Lighthouse's examination extends to Progressive Web App (PWA) features, ensuring your website aligns with modern web capabilities.

Whether you're a web developer aiming for optimal performance, an SEO professional strategizing for higher rankings, or a website owner dedicated to delivering an exceptional user experience, mastering Google Lighthouse is a game-changer. This guide will navigate you through the intricacies of Google Lighthouse, from understanding its metrics to implementing strategies for continuous improvement. Let's embark on a journey to unlock the full potential of your website's speed with Google Lighthouse.

Understanding Google Lighthouse: Decoding the Metrics and Categories

Google Lighthouse is not just a tool; it's your website's performance auditor, meticulously evaluating various aspects that contribute to an optimal user experience. To harness its power effectively, let's delve into the core metrics and categories that define the Google Lighthouse analysis.

Performance: Speeding into Success

At the forefront of Google Lighthouse's evaluation is the Performance category. This metric assesses how swiftly your website loads and how quickly users can interact with it. Through a set of crucial speed metrics, including First Contentful Paint (FCP), Largest Contentful Paint (LCP), Total Blocking Time (TBT), Cumulative Layout Shift (CLS), and Speed Index (SI), Lighthouse assigns a performance score ranging from 0 to 100. A higher score signifies a well-optimized user experience, while lower scores indicate potential performance issues. Understanding these metrics empowers you to enhance your website's loading speed systematically.

Accessibility: Ensuring Inclusivity

Lighthouse's Accessibility category focuses on making your website inclusive for users of all abilities. Analyzing elements such as buttons, links, and image alt text gauges how well assistive technologies can navigate and interpret your site. The score, ranging to 100, reflects the website's accessibility, with higher scores indicating better inclusivity. Leveraging this insight, you can enhance your website's accessibility and cater to a broader audience.

Best Practices: Building on Solid Foundations

The Best Practices category examines whether your website adheres to modern web development standards. From secure server connections (HTTPS) to valid HTML doctype and protection against cross-site scripting (XSS) attacks, Lighthouse evaluates various factors. A score out of 100 indicates how well your website aligns with best practices. Addressing the highlighted elements for improvement can elevate your website's foundation in the digital landscape.

SEO: Navigating the Search Landscape

For those seeking higher search engine rankings, the SEO category in Google Lighthouse is a valuable guide. It assesses technical SEO aspects, including mobile-friendliness, valid structured data, crawlable internal links, and more. The score, up to 100, provides insights into your website's SEO health. While the Lighthouse score doesn't directly impact SEO, addressing the identified issues can contribute to an SEO-friendly website.

Progressive Web App (PWA): Embracing Modern Capabilities

The PWA category validates whether your web application utilizes modern web capabilities and provides an optimal user experience. Lighthouse checks factors such as speed on mobile networks, offline functionality, and adherence to PWA best practices. Unlike other categories, PWA receives badges instead of scores, emphasizing the importance of embracing progressive web app features.

Understanding these categories and the associated metrics equips you with the knowledge to interpret your Google Lighthouse reports effectively.

A Step-by-Step Guide to Testing Your Website Speed with Google Lighthouse

Now that we've unraveled the intricacies of Google Lighthouse metrics let's test your website's speed and performance using this powerful tool. Follow this step-by-step guide to ensure a thorough analysis of your website's critical aspects.

Step 1. Choose Your Testing Platform

Google Lighthouse offers multiple testing platforms, each with its unique advantages. Consider the following options:

  • PageSpeed Insights: This is Google's official page speed tool, built on top of Lighthouse. It provides user data from the Chrome User Experience Report (CrUX) and Lighthouse reports.
  • Chrome DevTools: Integrated directly into Chrome's developer tools, this option offers more configuration choices. It's ideal for users familiar with Chrome's development environment.
  • Node Module: For advanced users with Node.js installed, the command-line interface allows for scriptable and customizable testing.

Choose the platform that aligns with your preferences and requirements.

Step 2. Enter Your Website URL

Once you've selected your testing platform, enter your website's URL to initiate the speed test, which initiates the Lighthouse analysis, scrutinizing your website's performance, accessibility, best practices, and SEO.

Step 3. Interpret the Results

Upon completing the test, you'll receive a comprehensive Lighthouse report. Focus on the following key elements:

  • Performance Score: A high-level score indicating overall performance. Scores between 90 and 100 suggest optimal user experience, while scores below 90 may signal areas for improvement.
  • Individual Metrics: Explore metrics such as First Contentful Paint (FCP), Largest Contentful Paint (LCP), Total Blocking Time (TBT), Cumulative Layout Shift (CLS), and Speed Index (SI). These offer granular insights into specific aspects of your website's speed.
  • Opportunities and Diagnostics: Lighthouse provides actionable opportunities for improvement and diagnostic information. Addressing these can lead to performance enhancements.

Step 4. Run Lighthouse on Different Configurations

Experiment with running Lighthouse tests on various configurations, such as mobile vs. desktop. Different configurations impact network conditions, latency, and CPU speed, providing a holistic view of your website's performance across devices.

Step 5. Utilize Chrome DevTools for In-Depth Analysis

If you opt for Chrome DevTools, use the advanced configuration options. Choose between simulated throttling or DevTools throttling, allowing you to tailor the testing environment for more accurate results.

Step 6. Monitor Your Scores Over Time

Website performance is dynamic. Regularly test your website with Google Lighthouse and monitor score changes over time. By following these steps, you can proactively manage and enhance your website's speed and performance.

Diving Deeper into Lighthouse Metrics

Understanding the nuances of Lighthouse metrics is crucial for unlocking the full potential of this powerful tool. Let's delve deeper into the critical performance indicators assessed by Lighthouse and how they contribute to your website's overall health.

Performance Metrics Explained

Lighthouse evaluates your website's performance through five core metrics:

  • Total Blocking Time (TBT): Measures the page's duration as unresponsive to user inputs due to excessive CPU processing.
  • Largest Contentful Paint (LCP): Quantifies the time it takes for the main page content to load, offering insights into user-perceived loading speed.
  • Cumulative Layout Shift (CLS): Assesses the stability of your page's layout by measuring unexpected shifts in content, preventing a disorienting user experience.
  • First Contentful Paint (FCP): Indicates how quickly users see the first content element on your page, providing an initial impression of loading speed.
  • Speed Index (SI): Measures the speed at which your page's content appears in front of the user. A lower score indicates faster loading speeds.

Understanding the contribution of each metric to your overall Lighthouse Performance score empowers you to pinpoint areas that require improvement.

Lighthouse Performance Score Breakdown

Unraveling the components that determine your Performance score:

  • Total Blocking Time (30%): Assessing the impact of CPU processing on user interactions.
  • Largest Contentful Paint (25%): Evaluating how quickly essential page content loads.
  • Cumulative Layout Shift (25%): Ensuring stability in page layout during user interaction.
  • First Contentful Paint (10%): Measuring the speed of the initial content appearance.
  • Speed Index (10%): Analyzing the time it takes for most page content to display.

By comprehending each metric's weight, you can strategically address areas with the most significant impact on your website's performance.

Calculating Lighthouse Performance Score

Unlocking the formula behind your website's Performance score:

  • Subscores: Each metric receives a subscore based on specific criteria and performance thresholds.
  • Weighted Contribution: Subscores are combined using assigned weights to form the overall Performance score.
  • Score Range (0-100): The final score ranges from 0 to 100, with higher scores signifying superior website optimization.

Click the "See Calculator" link in the Lighthouse report to explore the detailed score breakdown. This data provides a transparent view of how your website's Performance score is derived.

Running Lighthouse Tests in Various Modes

Leveraging different testing modes for tailored insights:

  • Navigation Mode: Reloads the page, grading performance, accessibility, and SEO.
  • Timespan Mode: Collects data on an open page, measuring the duration of page interactions.
  • Snapshot Mode: Analyzes accessibility and SEO based on the current page state.

Experimenting with these modes allows you to gather nuanced data and adapt Lighthouse testing to your needs.

With a deeper understanding of Lighthouse metrics, you can now interpret your website's performance reports and strategically enhance its speed and user experience.

Running Lighthouse Tests in Chrome DevTools

Google Chrome DevTools provides a convenient environment for conducting Lighthouse tests, offering valuable insights into your website's performance, accessibility, and SEO. Follow these steps to run Lighthouse tests seamlessly within the Chrome browser.

Begin by navigating to the webpage you intend to test. Right-click anywhere on the page and select "Inspect" from the context menu to open the DevTools panel. Once in the DevTools panel, locate and click on the "Lighthouse" tab. If you can't find it, clicking the two arrows at the end of the toolbar will reveal the option.

Within the Lighthouse tab, you can choose specific categories for analysis, including performance, accessibility, SEO, and more. Click on the "Analyze page load" button to kickstart the test.

As the page reloads, Lighthouse will swiftly generate test results within approximately a minute. The comprehensive report provides scores for each category and specific recommendations for improvement.

Chrome DevTools offers three distinctive modes for Lighthouse tests. The "Navigation" mode reloads the page, assessing performance, accessibility, and SEO. The "Timespan" mode collects data on an already open page, measuring the duration of page interactions. Lastly, the "Snapshot" mode analyzes accessibility and SEO based on the current state of the page.

For a more realistic assessment, configure throttling by clicking on the gear icon at the top right corner to access advanced Lighthouse settings. Opt for the DevTools throttling option, which allows you to simulate network conditions closely mimicking real-world scenarios, which ensures more reliable data for comprehensively evaluating your website's performance.

Running Lighthouse tests in Chrome DevTools is particularly useful for scenarios where you need to test local servers and pages requiring login or analyze user interactions as part of the speed test. Experiment with different modes and configurations to tailor your Lighthouse tests to specific testing scenarios.

Evaluating Lighthouse Data Reliability

While Google Lighthouse is a powerful tool for assessing website performance, accessibility, and SEO, it's essential to understand the factors influencing the reliability of the data it provides. Here are vital considerations to keep in mind when evaluating Lighthouse data.

Lighthouse operates in different modes, with the default mode being simulated throttling. However, this mode may occasionally produce inaccurate data due to its inherent limitations. When running Lighthouse tests on the same website multiple times, variations in performance scores are normal as each test captures data from a single page load.

A notable difference arises when comparing simulated throttling with accurate user metrics. PageSpeed Insights often indicates metrics that appear worse than the actual user data gathered by Lighthouse. This discrepancy is attributed to Lighthouse using significantly inferior network conditions in its simulation compared to the more typical experiences of real users. While Lighthouse's simulated metrics represent the slowest 5-10% of user experiences, Google's user metrics consider the 75th percentile.

Lighthouse utilizes observed metrics collected on a fast connection during its initial test, followed by a simulation to estimate page loading on a slower network. Although this approach allows for quick testing, it may introduce inaccuracies. Tools like the Site Speed Chrome extension can provide insights by revealing simulated metrics and original observed data, offering a comprehensive perspective.

For more reliable and high-quality data, it is advisable to use dedicated website speed testing tools like DebugBear. DebugBear's tests collect metrics directly in a throttled environment, ensuring more accurate and trustworthy results. Additionally, DebugBear facilitates continuous monitoring of your website's performance, allowing you to track changes over time, receive alerts for score regressions, and comprehend the impact of optimizations.

By acknowledging the nuances in Lighthouse data collection and exploring alternative tools like DebugBear, you can enhance the reliability of your website speed test results.

Addressing Lighthouse Troubleshooting

While Google Lighthouse is a powerful tool for evaluating website performance, discrepancies and troubleshooting issues may arise. Understanding and addressing common challenges can ensure a more accurate representation of your website's speed. Here are vital considerations for troubleshooting Lighthouse-related concerns:

It's not uncommon to notice variations between Lighthouse metrics and the user data recorded by Core Web Vitals. These variations can be due to Lighthouse's simulated throttling with network conditions that may significantly differ from actual user experiences. Lighthouse metrics typically represent the slowest 5-10% of user interactions, while Core Web Vitals focus on the 75th percentile, leading to disparities in reported scores.

One key factor contributing to score differences is the network conditions simulated by Lighthouse, which might be more severe than what typical users experience. The tool often simulates higher latency and lower bandwidth, resulting in lower page speed scores. Awareness of these differences in network conditions and making adjustments during testing can provide a more accurate reflection of real user experiences.

Depending on the same website, lighthouse scores can exhibit variability between runs due to random resource loading times, content changes, and background activities during testing. Understand that Lighthouse scores offer insights based on individual page loads, so you should expect variations in Lighthouse test results. Therefore, continuous monitoring and trend analysis over time can provide a more comprehensive understanding of your website's performance.

Comparing Lighthouse scores across different environments, such as PageSpeed Insights and local computers, may yield different results. Discrepancies can arise from differences in CPU speed, server proximity, and other environmental factors. Recognizing that scores obtained from different environments serve distinct purposes, with local tests reflecting faster CPU speeds, is crucial. At the same time, PageSpeed Insights aims to provide insights into real-world user experiences.

Addressing these troubleshooting considerations allows you to navigate discrepancies and optimize your website based on a more accurate performance assessment.

Take it From Us

Ensuring your website delivers an exceptional user experience is paramount in the fast-paced digital landscape. Google Lighthouse emerges as a powerful ally, offering a comprehensive analysis of your website's performance, accessibility, SEO, and more.

As we conclude this guide, the journey doesn't end with a single test or optimization effort. Instead, it extends into a commitment to continuous monitoring, proactive troubleshooting, and a dedication to delivering a top-notch user experience. By integrating the insights gained from Google Lighthouse, you empower your team to adapt, optimize, and stay ahead in the ever-evolving landscape of web performance. May your website's journey be swift, seamless, and always user-centric.