Use Google Lighthouse
Run a free website audit and find out exactly what to fix.
What this covers: Running Lighthouse audits via PageSpeed Insights or Chrome DevTools, interpreting scores across performance, SEO, accessibility, and best practices, and prioritizing fixes by impact.
Who it’s for: Site owners and developers who want a concrete, prioritized list of what to improve on their website using a free tool.
Key outcome: You’ll have Lighthouse scores for your key pages, understand what each metric means, and know which high-impact fixes (image optimization, render-blocking resources, contrast) to tackle first.
Time to read: 7 minutes
Part of: Technical Performance series
Google Lighthouse scores your website on performance, SEO, accessibility, and security. It’s like a report card that shows what’s slowing you down or hurting your rankings.
This guide covers: How to run a Lighthouse test, understand your scores, and prioritize fixes.
Run Your First Test
The easiest method (no installation):
- Go to PageSpeed Insights
- Enter your website URL
- Click Analyze
- Wait 30-60 seconds
You’ll get scores from 0-100 in four categories.
Alternative: Chrome DevTools
- Open your site in Chrome
- Press F12 (or right-click → Inspect)
- Go to the Lighthouse tab
- Click Analyze page load
This runs locally and gives you the same report.
Understanding Your Scores
| Score | What It Means |
|---|---|
| 90-100 (Green) | Good. No urgent action needed. |
| 50-89 (Orange) | Needs improvement. Address when time allows. |
| 0-49 (Red) | Poor. This is hurting your site. Fix soon. |
The Four Categories
Performance (Priority 1)
How fast your site loads. This directly affects:
- Bounce rate (slow sites lose visitors)
- Conversions (every second costs sales)
- Google rankings (Core Web Vitals are ranking factors)
Key metrics to watch:
- LCP (Largest Contentful Paint) – When your main content appears. Target: under 2.5 seconds.
- CLS (Cumulative Layout Shift) – Does content jump around? Target: under 0.1.
- TBT (Total Blocking Time) – How long before users can interact. Target: under 200ms.
SEO (Priority 2)
Basic technical SEO checks. A low score here means Google may have trouble reading your site.
Common issues: Missing meta descriptions, images without alt text, unindexable pages.
Accessibility (Priority 3)
Can everyone use your site? This checks color contrast, button sizes, screen reader compatibility.
Beyond compliance, accessibility issues often overlap with usability issues for all users.
Best Practices (Priority 4)
Security and web standards. HTTPS, avoiding deprecated APIs, console errors.
What to Fix First
Lighthouse shows a list of “Opportunities” and “Diagnostics” below each score. They’re sorted by impact.
High-Impact Performance Fixes
| Issue | Fix |
|---|---|
| “Serve images in next-gen formats” | Convert to WebP. WordPress: use Imagify or ShortPixel |
| “Properly size images” | Don’t upload 4000px images for 800px displays. Resize before uploading. |
| “Eliminate render-blocking resources” | WordPress: use Autoptimize or WP Rocket |
| “Enable text compression” | Enable GZIP on your server. Most hosts do this automatically. |
| “Reduce unused JavaScript/CSS” | Often from unused plugins. Audit and remove what you don’t need. |
Quick SEO Wins
- Missing meta description: Add one in your SEO plugin (Yoast, RankMath)
- Images missing alt text: Go to Media Library, add descriptive alt text
- Document doesn’t have a title: Every page needs a unique
<title>tag
Test Multiple Pages
Don’t just test your homepage. Different pages often have different issues:
- Homepage (usually optimized)
- A blog post (may have unoptimized images)
- Product page (may have heavy scripts)
- Contact page (may have embedded maps/forms)
Sources
Google Lighthouse Questions Answered
What is a good Lighthouse score?
A score of 90-100 is considered good, 50-89 needs improvement, and below 50 is poor. Aim for 90+ on Performance and Accessibility. Most production sites score between 60-80 on Performance due to third-party scripts and dynamic content.
Why do Lighthouse scores vary between runs?
Scores fluctuate due to network conditions, CPU load, browser extensions, and server response variability. Run Lighthouse in Incognito mode with extensions disabled, and average at least 3-5 runs for a reliable baseline. Use PageSpeed Insights for more stable results since it tests from Google’s servers.
What is the difference between Lighthouse and PageSpeed Insights?
Lighthouse is an open-source auditing tool that runs locally in your browser or CI pipeline. PageSpeed Insights runs Lighthouse on Google’s servers and combines it with real-world Chrome User Experience Report (CrUX) data from actual visitors, giving you both lab and field metrics.
How do you run Lighthouse in CI/CD?
Use the Lighthouse CI package (@lhci/cli) in your build pipeline. Configure it to run against a staging URL after deployment and set performance budgets that fail the build if scores drop below your thresholds. This prevents performance regressions from reaching production.
✓ Running Your First Lighthouse Audit
- Performance score is 50+ (ideally 90+)
- SEO score is 90+ (usually easy to achieve)
- No red items in “Opportunities” remain
Note: Scores vary between tests. Run 3 times and look at the average. Mobile scores are typically lower than desktop.
Lighthouse Scoring Questions
Is Lighthouse the same as PageSpeed Insights?
Almost. PageSpeed Insights runs Lighthouse in the cloud and adds real-user data (Core Web Vitals from actual visitors). Running Lighthouse in Chrome DevTools only shows lab data—what the tool measured, not what real users experience.
Why do my Lighthouse scores change each time?
Lighthouse runs in your browser, so your computer’s resources affect results. Network variability, browser extensions, and even other tabs impact scores. For consistent results, use Incognito mode and close other applications.
What score should I aim for?
Performance 70+, Accessibility 90+, Best Practices 90+, SEO 90+. Perfect 100s aren’t necessary—above 90 shows diminishing returns. Focus on Core Web Vitals (LCP, INP, CLS) rather than the overall performance number.
Should I follow every Lighthouse recommendation?
No. Some recommendations conflict with business needs (removing analytics to save milliseconds, for example). Prioritize high-impact items: image optimization, caching, reducing unused JavaScript. Ignore suggestions that break functionality.