Mastering Web App Speed with Lighthouse & Custom Audits

Users abandon slow websites. Google ranks fast ones higher. So how do you improve performance consistently? In this guide, we’ll go beyond basics — using Lighthouse to debug, fix, and even create custom audits for real performance gains.

🚀 Why Performance Matters

• Faster websites reduce bounce rate and increase conversion.
• Google’s Core Web Vitals are ranking factors.
• Mobile-first speed is crucial — especially for eCommerce and SaaS.

🔍 Step 1: Audit with Lighthouse in DevTools

Open your website in Chrome, open DevTools (F12), go to the Lighthouse tab, select 'Performance', and run an audit.

📊 Key Metrics to Watch

• **LCP (Largest Contentful Paint)** – Should be under 2.5s.
• **CLS (Cumulative Layout Shift)** – Keep below 0.1 for good UX.
• **TBT (Total Blocking Time)** – Affects responsiveness; aim under 300ms.

🧰 Step 2: Fix What Matters

npm install next-optimized-images react-lazyload

Examples of fixes:

• Use lazy loading: `<img loading='lazy' />`
• Compress images: WebP or AVIF formats
• Split long JS tasks using `requestIdleCallback()`

🧪 Step 3: Create a Custom Lighthouse Audit

Advanced teams can extend Lighthouse. For example, ensure every page includes structured data:

// Custom audit: Check for JSON-LD script tag
module.exports = class StructuredDataAudit {
  static get meta() {
    return { id: 'structured-data', title: 'Structured Data Audit', ... };
  }
  static audit(artifacts) {
    const hasLD = artifacts.SomePageHTML.includes('<script type="application/ld+json">');
    return { score: hasLD ? 1 : 0 };
  }
};

📘 Summary

• Use Lighthouse to find real performance bottlenecks
• Prioritize Core Web Vitals
• Implement smart lazy loading and optimization techniques
• Create custom audits for team-specific standards

Download custom audit templates