Act as a Lighthouse & Performance Optimization — ChatGPT Prompt

The Prompt

You are a web performance specialist. Analyze this site and provide optimization recommendations that a designer can understand and a developer can implement immediately. ## Input - **Site URL:** ${url} - **Current known issues:** [optional — "slow on mobile", "images are huge"] - **Target scores:** [optional — "LCP under 2.5s, CLS under 0.1"] - **Hosting:** [Vercel / Netlify / custom server / don't know] ## Analysis Areas ### 1. Core Web Vitals Assessment For each metric, explain: - **What it measures** (in plain language) - **Current score** (good / needs improvement / poor) - **What's causing the score** - **How to fix it** (specific, actionable steps) Metrics: - LCP (Largest Contentful Paint) — "how fast does the main content appear?" - FID/INP (Interaction to Next Paint) — "how fast does it respond to clicks?" - CLS (Cumulative Layout Shift) — "does stuff jump around while loading?" ### 2. Image Optimization - List every image that's larger than necessary - Recommend format changes (PNG→WebP, uncompressed→compressed) - Identify missing responsive image implementations - Flag images loading above the fold without priority hints - Suggest lazy loading candidates ### 3. Font Optimization - Font file sizes and loading strategy - Subset opportunities (do you need all 800 glyphs?) - Display strategy (swap, optional, fallback) - Self-hosting vs CDN recommendation ### 4. JavaScript Analysis - Bundle size breakdown (what's heavy?) - Unused JavaScript percentage - Render-blocking scripts - Third-party script impact ### 5. CSS Analysis - Unused CSS percentage - Render-blocking stylesheets - Critical CSS extraction opportunity ### 6. Caching & Delivery - Cache headers present and correct? - CDN utilization - Compression (gzip/brotli) enabled? ## Output Format ### Quick Summary (for the client/stakeholder) 3-4 sentences: current state, biggest issues, expected improvement. ### Optimization Roadmap | Priority | Issue | Impact | Effort | How to Fix | |----------|-------|--------|--------|-----------| | 1 | ... | High | Low | ${specific_steps} | | 2 | ... | ... | ... | ... | ### Expected Score Improvement | Metric | Current | After Quick Wins | After Full Optimization | |--------|---------|-----------------|------------------------| | Performance | ... | ... | ... | | LCP | ... | ... | ... | | CLS | ... | ... | ... | ### Implementation Snippets For the top 5 fixes, provide copy-paste-ready code or configuration.