Google Lighthouse is an invaluable tool for developers, SEO specialists, and website owners who want to improve their site’s performance, accessibility, and best practices. It provides insights into what’s slowing down a webpage and offers actionable recommendations. However, many people make mistakes when using Lighthouse, leading to misinterpretations and ineffective optimizations.
If you’ve been using Lighthouse and not seeing the improvements you expected, you might be falling into one of these common traps.
1. Running Lighthouse Tests in an Uncontrolled Environment
The Mistake
Many developers run Google Lighthouse audits directly in their main browser session while other applications are running in the background. This can lead to inconsistent or misleading results because the audit depends on real-time system conditions.
For example:
- If you have multiple browser tabs open, your system’s CPU and memory usage might fluctuate, affecting the audit’s performance metrics.
- Running Lighthouse over an unstable internet connection can result in slower page loads, causing a low Performance Score.
How to Avoid It
To get accurate and reliable results, you should:
✅ Use Chrome in Incognito Mode – This ensures no extensions interfere with the audit.
✅ Close Unnecessary Applications – Keep your system resources focused on the test.
✅ Use Lighthouse via Google PageSpeed Insights – This runs the audit on Google’s servers, eliminating local machine variations.
✅ Throttle CPU and Network Speed – Use Lighthouse’s built-in throttling to simulate real-world conditions.
By testing in a controlled environment, your results will be much more accurate and actionable.
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2. Only Checking the Home Page
The Mistake
A common misconception is that optimizing the homepage alone will drastically improve your entire website’s Lighthouse score. However, Google Lighthouse evaluates individual pages, not the entire site.
Your homepage might score well, but other crucial pages—such as product pages, blog posts, or checkout pages—could still have performance issues.
How to Avoid It
✅ Audit Multiple Pages – Run Lighthouse tests on landing pages, blog posts, and high-traffic areas of your website.
✅ Focus on Core User Journeys – Optimize the pages where users interact the most, such as sign-up forms and checkout pages.
✅ Use Crawlers to Identify Slow Pages – Tools like Screaming Frog can help you detect underperforming pages across your site.
Remember: Every page is different, and optimizing only the homepage won’t necessarily improve your site’s overall performance.
3. Ignoring Mobile Performance Scores
The Mistake
Many developers focus solely on the Desktop Lighthouse score, assuming that if a website loads fast on desktop, it will perform just as well on mobile. This is a critical mistake because mobile users typically experience slower network conditions, less powerful processors, and different interaction patterns.
Google’s Mobile-First Indexing means that your mobile performance matters more than your desktop score for SEO rankings.
How to Avoid It
✅ Always Run Lighthouse Audits in Mobile Mode – Use the mobile tab in Lighthouse to simulate a real-world mobile experience.
✅ Optimize for Slow Networks – Test on 3G or 4G throttling instead of high-speed broadband.
✅ Reduce JavaScript Execution Time – Mobile devices struggle with heavy JS files; minimize unnecessary scripts.
✅ Enable Responsive Images (srcset, WebP) – Large images are a major bottleneck on mobile. Use modern image formats and responsive images.
Focusing on mobile performance ensures that your site loads quickly for the majority of your users and ranks better on Google.
4. Chasing a Perfect 100 Lighthouse Score
The Mistake
While a 100/100 Lighthouse score might look impressive, it doesn’t necessarily mean your website is fully optimized. Many developers obsess over hitting a perfect score, often at the expense of actual user experience.
For example:
- You might disable certain features (like animations or third-party scripts) just to boost your score, making the site less engaging.
- You could over-optimize images to the point where they lose quality.
- A “perfect” score today doesn’t mean the site will perform the same way next month as content changes.
How to Avoid It
✅ Focus on Meaningful Metrics – Instead of chasing 100, aim for a balance between performance and functionality.
✅ Prioritize Core Web Vitals – Google’s ranking algorithm emphasizes Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS) more than a raw Lighthouse score.
✅ Test on Real Devices – Even if Lighthouse says your site is fast, real-world users may experience delays due to hardware and network variations.
Aiming for a fast and smooth user experience is more important than a perfect Lighthouse score.
5. Not Fixing Render-Blocking Resources
The Mistake
Many developers overlook render-blocking resources, such as large CSS or JavaScript files that delay the first paint of a webpage. These files prevent the browser from rendering the page quickly, leading to poor user experience and lower Lighthouse scores.
How to Avoid It
✅ Minify and Defer JavaScript – Use defer or async attributes for non-essential scripts.
✅ Use Critical CSS – Inline the most important styles for above-the-fold content while lazy-loading the rest.
✅ Implement Lazy Loading for Images and Videos – This prevents unnecessary resources from loading too early.
✅ Use a Content Delivery Network (CDN) – CDNs help distribute static files efficiently, reducing load times.
By addressing render-blocking issues, your site will load significantly faster, improving both user experience and SEO rankings.
6. Ignoring Third-Party Scripts and Ads
The Mistake
Third-party scripts—such as Google Analytics, Facebook Pixel, chat widgets, and ad networks—can heavily impact page load speed. Many site owners blindly add external scripts without considering their performance impact.
Excessive third-party requests can:
- Increase Total Blocking Time (TBT) and First Contentful Paint (FCP) delays.
- Cause Layout Shifts, which negatively affect user experience.
- Reduce Lighthouse Performance Scores significantly.
How to Avoid It
✅ Audit Third-Party Scripts – Remove or delay unnecessary tracking scripts, widgets, and ads.
✅ Use a Tag Manager – Google Tag Manager allows you to load scripts only when needed, preventing unnecessary slowdowns.
✅ Self-Host Critical Scripts – Hosting key scripts on your server can sometimes be faster than relying on third-party CDNs.
✅ Load Ads Responsibly – Use lazy loading for ads so they don’t impact initial page speed.
Reducing reliance on third-party scripts ensures a faster, more stable website.
Final Thoughts
Google Lighthouse is a powerful tool, but using it incorrectly can lead to misleading insights and wasted effort. By avoiding these six common mistakes, you can use Lighthouse effectively to improve your website’s speed, usability, and SEO.
Key Takeaways
→ Run tests in a controlled environment.
→ Audit multiple pages, not just the homepage.
→ Prioritize mobile performance over desktop.
→ Don’t chase a perfect score—focus on user experience.
→ Fix render-blocking resources to speed up page load times.
→ Reduce third-party scripts to keep your site lightweight.
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