Website Performance Optimization and Core Web Vitals Compliance Guide

Website performance directly affects user experience, SEO ranking, and conversion rate. Google uses Core Web Vitals as a ranking factor, making performance optimization a required course in website building.

1. Core Web Vitals Metrics

Three core metrics: ① LCP (Largest Contentful Paint): measures main content loading speed, target <2.5s (good), 2.5–4s needs improvement, >4s poor; ② FID (First Input Delay, to be replaced by INP): measures interaction response speed, target <100ms; ③ CLS (Cumulative Layout Shift): measures page stability, target <0.1. These three metrics correspond to loading, interaction, and visual stability respectively.

2. Image Optimization Techniques

Images typically account for over 50% of page size and are an optimization priority: ① use modern formats (WebP 25–35% smaller than JPEG, AVIF even smaller); ② responsive images (srcset loads different sizes based on screen); ③ lazy loading (loading="lazy", delay loading below-the-fold images); ④ image compression (TinyPNG, Squoosh, visually lossless compression); ⑤ CDN distribution (images accelerated via CDN edge nodes); ⑥ avoid layout shift (set width and height attributes for images). Using automated tools (e.g., Imagify, ShortPixel) for batch optimization is recommended.

3. Code Optimization Techniques

CSS optimization: ① concatenate and compress CSS files; ② inline critical CSS (above-the-fold styles directly in HTML); ③ remove unused CSS (PurgeCSS tool); ④ avoid @import. JavaScript optimization: ① compress and minify JS; ② lazy load non-critical JS (defer/async); ③ code splitting (load on demand); ④ remove unused libraries (e.g., unused jQuery plugins). HTML optimization: ① compress HTML (remove spaces and comments); ② reduce redirects; ③ preload critical resources (preload/preconnect).

4. Server and Cache Optimization

Server optimization: ① use CDN (static resource distributed acceleration, reduce origin load); ② enable Gzip/Brotli compression (text resources compressed 60–80%); ③ HTTP/2 or HTTP/3 (multiplexing, improve loading efficiency); ④ server response time <200ms (upgrade server config, optimize database queries). Cache strategy: ① browser cache (set Cache-Control, long-term cache for static resources); ② page cache (full-page cache, suitable for static pages); ③ database cache (Redis/Memcached, reduce database queries); ③ Service Worker (offline cache, PWA technology). Regularly using Lighthouse for detection, targeting performance score 90+, is recommended.