Anil

Posted on Jul 12 • Edited on Sep 10

How I Achieved a 100% Lighthouse Score with Next.js 15

Description: I built Format JSON Online using Next.js 15, Web Workers, and modern frontend optimizations to achieve a perfect Lighthouse score. Here's the full breakdown.

Tags: nextjs, performance, seo, webdev, lighthouse

👉 Live Demo: Format JSON Online

As a frontend developer obsessed with speed and SEO, I set out to answer:

Can I build a real-world developer tool that scores a perfect 100/100/100/100 on Google Lighthouse?

Spoiler: Yes, I did it.

Lighthouse Scores:

Performance: 100
Accessibility: 100
Best Practices: 100
SEO: 100 Tool: Format JSON Online

🔧 Tech Stack

Framework: Next.js 15 (App Router + Server Components)
Deployment: Vercel
Threading: Web Workers (for large JSON processing)
Styling: TailwindCSS (JIT mode)
Analytics: Plausible (privacy-friendly, lightweight)
Meta & SEO: Canonical URLs, OpenGraph, JSON-LD schema
Extras: TypeScript, Prettier, ESLint, SWC

🛠️ Optimization Techniques

1. 🧵 Web Workers for Heavy Lifting

JSON formatting, validation, and conversion are CPU-intensive. I offloaded these to Web Workers to keep the main UI thread free.

// jsonWorker.ts
self.onmessage = (e) => {
  const formatted = formatJSON(e.data);
  postMessage(formatted);
};

✅ No UI freezes

✅ Improved responsiveness on large files

2. ⚡ Next.js 15 + App Router

I used App Router, React Server Components, and Edge rendering:

Minimal client-side JS

Fast cold start performance

Route-level layouts and loading states

3. 🖋️ Fonts & Styling

Used system fonts — no Google Fonts

Zero-blocking CSS

TailwindCSS JIT purged all unused styles

4. 📸 Images & SVGs

Direct use of inline SVGs — no image bloat

Lazy-loaded icons and screenshots

No unoptimized external assets

5. 🚦 Lighthouse Checks in CI/CD

Before every deploy:

✅ Lighthouse score checked

✅ a11y rules enforced

✅ Bundle size thresholds monitored

Any score < 100 breaks the build.

6. 🔐 Smart Headers & Caching

Security Headers via Vercel + next.config.js

Cache-Control tuned per route

Static assets served with long-term caching

Minimal hydration — less JS shipped

🌟 Why It Matters

🟢 Blazing fast experience

🧠 Users stay longer & bounce less

🤖 Googlebot loves it (SEO++)

🔍 Better Core Web Vitals = Better Rankings

It's not just about dev bragging rights — performance directly impacts usability, conversion, and discoverability.

🧪 Try These Tools (All 100/100/100/100!)

📢 Final Thoughts

Reaching a perfect Lighthouse score isn’t just for static marketing pages — it's achievable on real-world apps with:

Next.js 15

Web Workers

Strong performance discipline

If you're building something similar, I hope this helps!
Got questions or want to share your setup? Drop a comment below.

🤝 Let’s Connect
🌐 Visit: https://formatjsononline.com

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