Web Performance Optimization

Optimize web performance through Core Web Vitals, modern browser APIs (View Transitions, Speculation Rules), and framework-specific techniques.

When to Use This Skill

• Improving Lighthouse scores (target: 90+)

• Reducing page load times (target: <2.5s LCP)

• Optimizing Core Web Vitals for SEO rankings

• Implementing modern performance patterns (2025)

• Debugging performance bottlenecks

• Setting up continuous performance monitoring

Business Impact: 1 second delay = 7% conversion loss. 0.1s improvement = 8% increase in conversions.

Start Here: Quick Wins

High-ROI optimizations by time investment:

1 Hour Quick Wins (⭐⭐⭐⭐⭐ ROI):

• Add loading="lazy" to below-fold images (40-60% weight reduction)

• Enable compression (gzip/brotli) (70-80% transfer size reduction)

• Add rel="preconnect" for critical origins (100-500ms savings)

1 Day Investments (⭐⭐⭐⭐ ROI):

• Implement code splitting (30-50% bundle reduction)

• Optimize LCP image with fetchpriority="high" (200-400ms improvement)

• Add basic service worker (instant repeat visits)

1 Week Comprehensive (⭐⭐⭐⭐⭐ ROI):

• Full caching strategy (HTTP headers + service workers)

• Bundle optimization (tree shaking, 40-60% reduction)

• Performance monitoring (Lighthouse CI + RUM)

→ See quick-wins.md for complete implementation details

Core Web Vitals at a Glance

Metric Target Weight Key Optimization

LCP (Largest Contentful Paint) <2.5s 25% Optimize images, preload critical resources

INP (Interaction to Next Paint) <200ms 30% Reduce JavaScript, break up long tasks

CLS (Cumulative Layout Shift) <0.1 25% Reserve space, optimize fonts

TBT (Total Blocking Time) <200ms 30% Code splitting, defer non-critical JS

FCP (First Contentful Paint) <1.8s 10% Eliminate render-blocking resources

→ See core-web-vitals.md for deep dive on each metric

Modern Patterns (2025)

View Transitions API - Smooth page transitions without JavaScript

@view-transition { navigation: auto; }

Speculation Rules API - Prerender pages for instant navigation

React Server Components - Zero-bundle server components

Priority Hints - fetchpriority="high" for LCP optimization

Content Visibility - CSS-based rendering optimization

→ See modern-patterns-2025.md for cutting-edge techniques

Navigation

Quick Start (Load First)

• ⚡ Quick Wins - Time-boxed optimizations (1hr/1day/1week) with ROI ratings. Load FIRST for immediate impact.

Deep Dives

• 📊 Core Web Vitals - LCP, INP, CLS optimization strategies with debugging workflows. Load when targeting specific metrics.

• 🔧 Optimization Techniques - Image, JavaScript, CSS, resource loading, caching patterns. Load when implementing specific optimizations.

Modern Features

• ✨ Modern Patterns 2025 - View Transitions, Speculation Rules, RSC, Islands Architecture. Load when adopting cutting-edge patterns.

Framework-Specific

• ⚛️ Framework Patterns - Next.js, React, Vue, Vite, Astro, SvelteKit optimizations. Load for your framework.

Measurement & Monitoring

• 📈 Monitoring - Lighthouse CI, RUM setup, performance budgets, debugging tools. Load when setting up continuous monitoring.

Key Reminders

• Measure first, optimize second - Always baseline with Lighthouse/WebPageTest before changes

• Focus on user-centric metrics - Core Web Vitals > vanity metrics

• Test on real devices - 53% of mobile users abandon after 3 seconds

• Monitor continuously - Performance degrades over time without vigilance

• Prioritize by ROI - Start with Quick Wins (high impact, low effort)

Red Flags

Stop and reconsider if:

• Optimizing without baseline measurement

• Focusing only on Lighthouse score (ignoring field data)

• Ignoring mobile performance (53% abandon rate after 3s)

• Loading all resources eagerly (no lazy loading)

• No caching strategy implemented

• Third-party scripts loaded synchronously

• Missing performance monitoring/budgets

Integration with Other Skills

• nextjs-core - Next.js Image component, font optimization, static generation

• react - Component optimization, memoization, code splitting

• vite - Build optimization, chunk splitting

• typescript-core - Type-safe performance patterns

Real-World Impact

Conversion Impact:

• Pinterest: 40% faster perceived wait = 15% more sign-ups + 15% more SEO traffic

• Zalando: 0.1s improvement = 0.7% revenue increase

• AutoAnything: 50% faster load = 12-13% sales increase

SEO Impact:

• Core Web Vitals are ranking factors (June 2021+)

• 75% of users passing Core Web Vitals = ranking boost

• Mobile-first indexing prioritizes mobile performance

Remember: Performance is a feature, not an afterthought. Every millisecond counts. Start with Quick Wins for immediate impact.