🌐 Network Performance Optimization Checklist

Table of Contents

1. Asset Optimization
2. Loading Strategy
3. HTTP & Transport
4. Caching Strategy
5. Images & Media
6. JavaScript Performance
7. API & Data Fetching
8. Monitoring & Measurement
9. Mobile & Low-Network Users
10. Dev & Build Setup
11. Bonus (Advanced)
12. Additional Optimizations

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📦 Asset Optimization

• [ ] Minify JS, CSS, HTML
• [ ] Use Brotli (preferred) or Gzip compression
• [ ] Remove unused CSS (PurgeCSS)
• [ ] Tree-shake unused JS exports
• [ ] Split bundles (code splitting)
• [ ] Use modern formats: .webp, .avif
• [ ] Use SVG instead of PNG/JPG when possible
• [ ] Remove duplicate dependencies
• [ ] Use CSS sprites for small icons
• [ ] Inline small critical assets (< 4KB)

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🚀 Loading Strategy

• [ ] Use defer for non-critical scripts
• [ ] Use async for independent scripts
• [ ] Lazy-load images (loading="lazy")
• [ ] Lazy-load routes/components
• [ ] Avoid render-blocking resources
• [ ] Inline critical CSS
• [ ] Load third-party scripts asynchronously
• [ ] Use rel="preconnect" for critical origins
• [ ] Implement resource hints (dns-prefetch, preconnect)
• [ ] Defer non-critical CSS loading

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📡 HTTP & Transport

• [ ] Use HTTP/2 or HTTP/3
• [ ] Reduce number of requests
• [ ] Enable keep-alive
• [ ] Avoid large request headers
• [ ] Use CDN for static assets
• [ ] Enable QUIC protocol where supported
• [ ] Optimize connection pooling
• [ ] Reduce redirect chains
• [ ] Use domain sharding strategically (HTTP/1.1 only)
• [ ] Minimize DNS lookups

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🧠 Caching Strategy

• [ ] Set proper Cache-Control headers
• [ ] Use immutable assets with hash-based filenames
• [ ] Cache API responses when safe
• [ ] Use Service Workers for offline + caching
• [ ] Implement stale-while-revalidate
• [ ] Configure ETags appropriately
• [ ] Use browser caching for static resources
• [ ] Implement memory caching for frequent data
• [ ] Cache DNS responses
• [ ] Use localStorage/sessionStorage wisely

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🖼️ Images & Media

• [ ] Serve responsive images (srcset, sizes)
• [ ] Compress images aggressively
• [ ] Avoid autoplay videos
• [ ] Stream large media instead of full download
• [ ] Use placeholders / blur-up technique
• [ ] Implement progressive JPEG loading
• [ ] Use <picture> element for art direction
• [ ] Lazy-load offscreen images
• [ ] Optimize image dimensions (don't serve oversized)
• [ ] Consider LQIP (Low Quality Image Placeholder)
• [ ] Use adaptive bitrate streaming for video
• [ ] Add decoding="async" to images

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⚡ JavaScript Performance

• [ ] Avoid large libraries when smaller alternatives exist
• [ ] Prefer dynamic imports
• [ ] Debounce/throttle network calls
• [ ] Batch API requests
• [ ] Cancel unnecessary fetches (AbortController)
• [ ] Use Web Workers for heavy computation
• [ ] Avoid blocking the main thread
• [ ] Optimize third-party script loading
• [ ] Remove console.log in production
• [ ] Use requestAnimationFrame for animations
• [ ] Avoid memory leaks (remove event listeners)
• [ ] Use intersection observer instead of scroll events

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🔁 API & Data Fetching

• [ ] Reduce payload size (send only needed fields)
• [ ] Use pagination / infinite scrolling
• [ ] Use GraphQL fragments or REST filtering
• [ ] Compress JSON responses
• [ ] Implement client-side caching (SWR / React Query)
• [ ] Use HTTP/2 server push for critical resources
• [ ] Implement request deduplication
• [ ] Use WebSocket for real-time data instead of polling
• [ ] Batch multiple API calls into one
• [ ] Implement optimistic UI updates
• [ ] Use delta updates instead of full payloads
• [ ] Implement proper rate limiting

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🧪 Monitoring & Measurement

• [ ] Measure TTFB, LCP, CLS, FID
• [ ] Use Lighthouse regularly
• [ ] Monitor slow network scenarios (3G/4G)
• [ ] Log failed or slow requests
• [ ] Track real-user metrics (RUM)
• [ ] Monitor Core Web Vitals
• [ ] Set up performance budgets
• [ ] Use performance profiling tools
• [ ] Track bundle size over time
• [ ] Monitor error rates and timeouts
• [ ] Use synthetic monitoring
• [ ] Measure INP (Interaction to Next Paint)

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📱 Mobile & Low-Network Users

• [ ] Optimize for slow connections
• [ ] Avoid heavy animations on load
• [ ] Reduce JavaScript execution time
• [ ] Provide offline fallback UI
• [ ] Implement adaptive loading based on connection
• [ ] Use Network Information API
• [ ] Reduce battery consumption
• [ ] Test on real mobile devices
• [ ] Optimize for touch interactions
• [ ] Reduce data usage with save-data header

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🛠️ Dev & Build Setup

• [ ] Enable production builds
• [ ] Analyze bundle size (webpack-bundle-analyzer)
• [ ] Use environment-based configs
• [ ] Avoid shipping source maps publicly
• [ ] Set correct MIME types
• [ ] Use modern build tools (Vite, esbuild)
• [ ] Enable tree-shaking in bundler
• [ ] Configure proper polyfills
• [ ] Use differential serving (modern/legacy bundles)
• [ ] Automate performance testing in CI/CD

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🧠 Bonus (Advanced)

• [ ] Prefetch important routes
• [ ] Preload critical assets
• [ ] Use edge caching
• [ ] Use partial hydration / islands
• [ ] Implement priority hints
• [ ] Use 103 Early Hints
• [ ] Implement streaming SSR
• [ ] Use module preloading
• [ ] Implement route-based code splitting
• [ ] Use import maps for dependencies
• [ ] Optimize font loading (font-display, preload)
• [ ] Implement progressive enhancement

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✨ Additional Optimizations

Security & Performance

• [ ] Use SRI (Subresource Integrity) for CDN assets
• [ ] Implement CSP (Content Security Policy)
• [ ] Use HSTS for secure connections
• [ ] Minimize third-party dependencies

Fonts

• [ ] Use system fonts when appropriate
• [ ] Subset fonts to required characters
• [ ] Use variable fonts to reduce variants
• [ ] Implement font-display: swap or optional
• [ ] Preload critical fonts
• [ ] Self-host fonts instead of Google Fonts

CSS Performance

• [ ] Avoid @import in CSS
• [ ] Minimize CSS specificity
• [ ] Use CSS containment
• [ ] Optimize CSS animations (use transform/opacity)
• [ ] Remove unused keyframes

Database & Backend

• [ ] Optimize database queries
• [ ] Use database connection pooling
• [ ] Implement database indexes
• [ ] Use Redis/Memcached for caching
• [ ] Enable database query caching
• [ ] Optimize N+1 queries

Forms & Validation

• [ ] Use client-side validation first
• [ ] Debounce form input validation
• [ ] Implement incremental validation
• [ ] Cache form state locally

Analytics & Tracking

• [ ] Load analytics scripts asynchronously
• [ ] Use server-side analytics when possible
• [ ] Batch analytics events
• [ ] Consider privacy-focused analytics (Plausible, Fathom)

Framework-Specific

• [ ] Use React.memo / useMemo / useCallback
• [ ] Implement virtual scrolling for long lists
• [ ] Use Suspense for data fetching
• [ ] Optimize re-renders
• [ ] Use production builds of frameworks

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📊 Performance Metrics Reference

Metric	Good	Needs Improvement	Poor
LCP	≤ 2.5s	2.5s - 4.0s	> 4.0s
FID	≤ 100ms	100ms - 300ms	> 300ms
CLS	≤ 0.1	0.1 - 0.25	> 0.25
TTFB	≤ 800ms	800ms - 1.8s	> 1.8s
INP	≤ 200ms	200ms - 500ms	> 500ms

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🔗 Useful Tools

• Performance Testing: Lighthouse, WebPageTest, Chrome DevTools
• Bundle Analysis: webpack-bundle-analyzer, source-map-explorer
• Image Optimization: Squoosh, ImageOptim, Sharp
• Monitoring: Sentry, New Relic, Datadog, Vercel Analytics
• CDN: Cloudflare, Fastly, AWS CloudFront
• Compression: Brotli, Gzip, Zstandard

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💡 Quick Wins Checklist

Start here for immediate impact:

1. Enable compression (Brotli/Gzip)
2. Optimize and compress images
3. Minify CSS/JS
4. Enable browser caching
5. Use a CDN
6. Lazy-load images
7. Remove unused CSS/JS
8. Use defer on scripts