A concise, actionable checklist of frontend performance best practices to help deliver fast, responsive, and efficient web experiences.
1. Minimize and compress JavaScript and CSS
Use tools like Terser for JS and cssnano for CSS to strip whitespace, comments, and shorten identifiers. Pair with Brotli or Gzip compression on the server to dramatically reduce transfer sizes.
2. Optimize and serve next-gen image formats
Convert images to WebP or AVIF, which offer 25–50% smaller file sizes than JPEG/PNG at equivalent quality. Use tools like Squoosh, Sharp, or build-pipeline plugins to automate conversion.
3. Implement lazy loading for images and iframes
Add the native `loading="lazy"` attribute to below-the-fold images and iframes so browsers defer their download until they approach the viewport, reducing initial page weight.
4. Use responsive images with srcset and sizes
Provide multiple image resolutions via the `srcset` attribute and define layout breakpoints with `sizes` so browsers download only the resolution appropriate for the device's screen, avoiding oversized downloads on mobile.
5. Apply code splitting and tree shaking
Use a bundler like Webpack or Vite to split JavaScript into smaller chunks loaded on demand, and enable tree shaking to eliminate unused exports, reducing initial bundle size and parse time.
6. Leverage browser caching with proper cache headers
Set long `Cache-Control: max-age` headers with content-hash filenames for static assets so returning visitors load them from disk instead of the network, and use short or `no-cache` headers only for HTML.
7. Eliminate render-blocking resources
Move non-critical CSS to load asynchronously (e.g., using `media` tricks or `rel=preload`) and defer or async-load JavaScript that is not needed for initial render to unblock the browser's rendering pipeline.
8. Preload critical assets
Use `<link rel="preload">` for above-the-fold fonts, hero images, and critical scripts so the browser discovers and fetches them early in the loading process, improving Largest Contentful Paint (LCP).
9. Minimize layout thrashing and forced reflows
Batch DOM reads before DOM writes, avoid reading layout properties (e.g., `offsetWidth`) inside loops, and prefer CSS transforms/opacity for animations as they run on the compositor thread without triggering layout.
10. Self-host and subset web fonts
Host fonts on your own origin to avoid DNS lookups to third parties, and use font subsetting tools like `pyftsubset` or Glyphhanger to include only the characters your site actually uses, cutting font file size significantly.
11. Implement a Content Delivery Network (CDN)
Serve static assets from a CDN with edge nodes geographically close to users to reduce latency. Configure CDN caching rules and ensure HTTP/2 or HTTP/3 is enabled for multiplexed parallel asset delivery.
12. Measure and monitor Core Web Vitals continuously
Track LCP, INP (Interaction to Next Paint), and CLS using tools like Lighthouse CI, WebPageTest, and the Chrome User Experience Report (CrUX). Set performance budgets and integrate checks into your CI/CD pipeline to catch regressions early.
13. Reduce third-party script impact
Audit all third-party tags (analytics, chat widgets, ads) with tools like Request Map or WebPageTest's waterfall. Load non-critical third parties with `defer` or `async`, or replace heavy libraries with lighter self-hosted alternatives where possible.
14. Use efficient CSS selectors and avoid large DOM trees
Keep the DOM node count under ~1500 elements as recommended by Lighthouse; large DOMs increase style recalculation and memory usage. Favor simple class-based CSS selectors over deeply nested or universal selectors to speed up style matching.