Lighthouse is an open source automated analysis tool, developed by the Google team, that lets you evaluate the quality of a web page against several technical parameters. The analysis produces a score from 0 to 100 for each monitored category and generates a detailed report with actionable guidance on how to improve performance and user experience.
Although it was created for the web application context, Lighthouse can also be used on static pages, e-commerce sites and web applications. Its use is fully part of the technical audit activities that precede a search engine optimization effort.
What it analyzes and how it returns results
Lighthouse is an automated audit tool that analyzes a web page by simulating loading on a configurable device and network connection. At the end of processing it returns a report structured by category, each with a summary score and a list of detected issues.
The tool is built into Chromium-based browsers, especially Chrome, where it is accessible from the developer tools panel. There is also a command-line version and a Node.js module, which let you automate checks within continuous integration pipelines. Lighthouse is also the engine that PageSpeed Insights runs to show the “lab” part of its report.
The four audit areas
Since version 12 (May 2024) Lighthouse organizes checks into four categories: performance, accessibility, best practices and SEO. The category dedicated to progressive web apps (PWA), present in earlier versions, has been removed. Each category has an independent score from 0 to 100.
Loading speed and responsiveness
The performance category measures how quickly the page loads and becomes usable. The score is a weighted average of five metrics: First Contentful Paint, Speed Index, Largest Contentful Paint, Total Blocking Time and Cumulative Layout Shift. Interaction to Next Paint (INP), which replaced First Input Delay in Core Web Vitals, requires a real user interaction and is not measured in the lab: Lighthouse uses Total Blocking Time as an indirect indicator of responsiveness.
Contrast, labels and semantic structure
This section checks compliance with the web content accessibility guidelines, verifying aspects such as color contrast, the presence of alternative text for images and the correct semantic structure of elements.
Security and correct API usage
Best practices collect a series of cross-cutting checks related to security, correct use of browser APIs and the overall technical consistency of the page.
The SEO elements checked
The SEO category checks only basic requirements: title and meta description present, crawlable links, page not blocked by robots.txt or a noindex tag, viewport attribute for mobile, alternative text for images. An SEO score of 100 does not mean the page is optimized: it says nothing about content, search intent, authority or competition.
Lab data and field data
Lighthouse produces lab data: it simulates loading with a preset device and network, so it is repeatable and suitable for finding problems, but it does not describe the real experience of users. Field data, collected from users’ browsers and visible in the Core Web Vitals report in Search Console and in PageSpeed Insights, is what Google considers for ranking. For this reason a high Lighthouse score does not guarantee that Core Web Vitals thresholds are met in the field, and vice versa.
The steps to start an analysis
Using Lighthouse requires a few steps and does not need advanced programming skills. The result depends largely on network conditions and the simulated device, so it is advisable to repeat the analysis several times.
- Open the page to analyze in the Chromium-based browser.
- Access the developer tools via the menu or the keyboard shortcut.
- Select the Lighthouse tab within the panel.
- Choose the categories to include in the report.
- Configure the device type, mobile or desktop.
- Start the analysis and wait for it to complete.
- Review the report and identify the items with the lowest scores.
- Apply the suggested fixes and repeat the check.
Frequently asked questions
Does Lighthouse replace a manual SEO audit?
No, Lighthouse only checks technical aspects that can be measured automatically. A complete audit also requires analysis of content, link profile and competition.
Does the Lighthouse score directly influence ranking?
The score itself is not a ranking factor. However, the parameters that make it up, such as loading speed, are relevant to user experience and indirectly to ranking.
Why do scores change between one analysis and another?
Measurements depend on variable factors such as network latency, server load and external resources. For this reason it is advisable to calculate an average over several runs.
Does Lighthouse also work on pages protected by authentication?
Yes, it is possible to analyze pages that require login, as long as the session is already active in the browser. Alternatively, dedicated configurations can be used.
What are the main limitations of the tool?
Lighthouse does not evaluate content quality or site authority. Moreover, the results are simulated and may differ from the real browsing conditions of users.
Are there alternatives to Lighthouse?
Yes, there are other web performance analysis tools, both commercial and open source, that offer partially overlapping functionality. The choice depends on goals and technical context.
From the glossary to the projectDoes your site meet the Core Web Vitals thresholds?Performance optimization works on loading speed and Core Web Vitals for a better user experience.Discover Core Web Vitals optimization