Performance 8 min read
Web Performance Optimization: Complete 2025 Guide
LC
Louis Cercle
Full-Stack Developer
In 2025, Google uses Core Web Vitals as a ranking factor. A slow site = fewer visitors, fewer conversions, less revenue. Here's how to optimize your site for perfect scores.
Core Web Vitals Explained
LCP
Largest Contentful Paint
Main content display time
Target: < 2.5s
INP
Interaction to Next Paint
Interaction responsiveness
Target: < 200ms
CLS
Cumulative Layout Shift
Visual page stability
Target: < 0.1
1. Optimize LCP
Preload Critical Resources
<!-- Preload LCP image -->
<link rel="preload" as="image" href="/hero.webp" fetchpriority="high">
<!-- Preload critical fonts -->
<link rel="preload" as="font" type="font/woff2"
href="/fonts/inter.woff2" crossorigin>
<!-- Preconnect to third-party domains -->
<link rel="preconnect" href="https://fonts.googleapis.com">2. Improve INP
Key Tip
Avoid long JavaScript tasks (>50ms) on the main thread. Use Web Workers for intensive calculations.
3. Reduce CLS
- Always define width/height on images and videos
- Reserve space for ads and embeds
- Avoid web fonts that cause FOIT/FOUT
- Animate with transform rather than top/left/width/height
Performance Checklist
- Images in WebP/AVIF with explicit dimensions
- Preload critical resources (LCP image, fonts)
- Lazy loading for below-the-fold content
- Minified and tree-shaken JavaScript
- Brotli compression enabled
- CDN configured with long cache
Conclusion
Web performance is not optional in 2025. Every millisecond counts for user experience and SEO. Use measurement tools, follow this checklist, and iterate. A fast site = happy users = a thriving business.