🚀 Frontend Performance Optimization Checklist: A one-stop solution to master Core Web Vitals

✅ 1. First Contentful Paint (FCP)

Target: < 1.8s

📌 First visual feedback to the user

✅ Best Practices:

• ⏩ Use CDN for static assets
• 🎯 Inline critical CSS
• 🧼 Minify & defer non-critical CSS/JS
• 🖼️ Optimize above-the-fold images
• 🔍 Preload key resources (<link rel="preload">)
• 🌐 Reduce server response time (use cache, edge computing)

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✅ 2. Largest Contentful Paint (LCP)

Target: < 2.5s

📌 Render the largest visible content quickly

✅ Best Practices:

• 🖼️ Use next-gen image formats: WebP, AVIF
• 🧊 Compress & resize hero images
• 📥 Preload the LCP image/font/asset
• 🚫 Avoid lazy-loading above-the-fold content
• 💡 Serve HTML quickly (SSR or static HTML for first load)

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✅ 3. Total Blocking Time (TBT)

Target: < 200ms

📌 Main thread responsiveness during load

✅ Best Practices:

• 🧠 Break large JavaScript tasks into chunks
• 🧵 Offload heavy computation to Web Workers
• ✂️ Reduce third-party scripts and tracking pixels
• 📦 Use code-splitting to reduce bundle size
• 💤 Lazy-load non-critical JS modules

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✅ 4. Cumulative Layout Shift (CLS)

Target: < 0.1

📌 Avoid unexpected visual shifts

✅ Best Practices:

• 🔲 Always define width and height for images/videos
• 📏 Reserve space for dynamic content (ads, iframes)
• 🔠 Use font-display: swap to avoid FOIT (Flash of Invisible Text)
• 🚫 Don’t insert DOM elements above existing content after page load
• 🎞️ Use transform, not top/left, for animations

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✅ 5. Speed Index

Target: < 3.4s

📌 How fast your page visually completes

✅ Best Practices:

• ⚡ Prioritize visible content first
• 🔃 Defer offscreen and background content
• 🧩 Preload critical resources (fonts, hero images)
• 🌍 Minimize redirects & DNS lookups
• 🛠️ Reduce dependency size (lodash, moment.js, etc.)

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🛠️ Tools You Can Use:

Tool	Use Case
💡 PageSpeed Insights	Google's official performance audit
🔍 Lighthouse (Chrome DevTools)	Local performance & SEO audit
⚡ WebPageTest	Visual load progress and request waterfall
🧪 GTmetrix	Page load speed and suggestions
📦 Bundlephobia	Check size of npm packages

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