Google Lighthouse is a free, automated tool designed to improve the quality of web pages. It is built directly into the Google Chrome browser and provides a comprehensive "health report" for any page, scoring it in five key areas.
Using it is the fastest way to identify technical issues and receive specific suggestions for improving your website's speed, accessibility, and overall performance.
Step-by-Step: How to Run a Report
The process is simple and requires no technical expertise. The easiest method is through Chrome's Developer Tools (DevTools).
1. Open an "Incognito" Window
- It is very important to run the test in an incognito window. This ensures that your own Chrome extensions or cached files do not interfere with the measurement results.
- How: Ctrl+Shift+N (on Windows) or Cmd+Shift+N (on Mac).
2. Navigate to Your Website
In the Incognito window, type the URL of the page you want to audit (e.g., your homepage, a product page, etc.).
3. Open Developer Tools (DevTools)
Right-click anywhere on the page and select "Inspect".
Alternatively: Press the F12 key (on Windows) or Cmd+Option+I (on Mac).
4. Find the "Lighthouse" Tab
In the DevTools window that just opened (usually on the right or bottom of the screen), you will see various tabs (Elements, Console, etc.). Click on the tab that says "Lighthouse". (If you don't see it, it might be hidden behind the >> arrow icon).
5. Configure the Report
Mode: Leave the "Navigation" option selected.
Device: Select "Mobile". This is the most critical setting. Google now primarily evaluates websites based on their mobile version (Mobile-First Indexing). Auditing on "Desktop" is useful, but the mobile audit is essential.
Categories: Ensure all five are checked: Performance, Accessibility, Best Practices, SEO.
6. Generate the Report
Click the blue "Analyze page load" or "Generate report" button.
Lighthouse will begin the process, simulating a visit from a mobile device. After about 30-60 seconds, it will present you with a detailed report.
What to Look For in the Results
You will see five (or four) scores, from 0 to 100. Your goal is to get as close to 100 as possible in every category, with a special focus on the following:
1. Performance
This is the most important (and usually the hardest) metric. It shows how quickly your page loads and becomes interactive for the user.
What to watch for:
- Largest Contentful Paint (LCP): How quickly does the largest element (usually the main image or a large block of text) appear on the screen? This measures perceived loading speed.
- Interaction to Next Paint (INP) / First Input Delay (FID): How quickly does the page "respond" when a user tries to do something (e.g., click a button)? This measures interactivity.
- Cumulative Layout Shift (CLS): Do elements on the page (like buttons or images) "jump" around as it loads? This measures visual stability and is very annoying for users.
- How to improve it: The Lighthouse report gives you specific "Opportunities". The most common ones are:
- "Optimize images" (e.g., use modern formats like WebP).
- "Reduce unused JavaScript".
- "Enable text compression" or "Leverage browser caching".
2. Accessibility
This metric shows how easily your website can be used by people with disabilities (e.g., with visual, hearing, or motor impairments).
What to watch for:
- Color Contrast: Is your text easily readable against its background?
- Alt Text: Do your images have alt descriptions for people using screen readers?
- Button Names: Do buttons have clear, descriptive labels?
3. Best Practices
This audit checks for modern web development standards and site security.
What to watch for:
- Uses HTTPS: Is your page secure?
- Browser Errors: Does the page log errors to the Console that the user can't see, but Google can?
- Proper Image Usage: Are images served with the correct aspect ratio?
4. SEO (Search Engine Optimization)
Lighthouse does not judge the quality of your content here, but it performs a basic technical SEO check.
What to watch for:
- Title and Meta Description: Does your page have a unique title and description?
- Crawlable Links: Are your links easy for Google to "read"?
- Mobile-Friendly: Although you're already testing for this, this confirms the page is set up correctly (has a viewport tag).
Using Lighthouse regularly (e.g., once a month or after major changes) is the best way to ensure your website remains fast, accessible, and friendly to search engines.
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