{"id":"4b49651c-9892-4f9b-bcde-acb38c3df398","shortId":"gtEFS8","kind":"skill","title":"performance-profiling","tagline":"Performance profiling principles. Measurement, analysis, and optimization techniques.","description":"# Performance Profiling\n\n> Measure, analyze, optimize - in that order.\n\n## 🔧 Runtime Scripts\n\n**Execute these for automated profiling:**\n\n| Script | Purpose | Usage |\n|--------|---------|-------|\n| `scripts/lighthouse_audit.py` | Lighthouse performance audit | `python scripts/lighthouse_audit.py https://example.com` |\n\n---\n\n## 1. Core Web Vitals\n\n### Targets\n\n| Metric | Good | Poor | Measures |\n|--------|------|------|----------|\n| **LCP** | < 2.5s | > 4.0s | Loading |\n| **INP** | < 200ms | > 500ms | Interactivity |\n| **CLS** | < 0.1 | > 0.25 | Stability |\n\n### When to Measure\n\n| Stage | Tool |\n|-------|------|\n| Development | Local Lighthouse |\n| CI/CD | Lighthouse CI |\n| Production | RUM (Real User Monitoring) |\n\n---\n\n## 2. Profiling Workflow\n\n### The 4-Step Process\n\n```\n1. BASELINE → Measure current state\n2. IDENTIFY → Find the bottleneck\n3. FIX → Make targeted change\n4. VALIDATE → Confirm improvement\n```\n\n### Profiling Tool Selection\n\n| Problem | Tool |\n|---------|------|\n| Page load | Lighthouse |\n| Bundle size | Bundle analyzer |\n| Runtime | DevTools Performance |\n| Memory | DevTools Memory |\n| Network | DevTools Network |\n\n---\n\n## 3. Bundle Analysis\n\n### What to Look For\n\n| Issue | Indicator |\n|-------|-----------|\n| Large dependencies | Top of bundle |\n| Duplicate code | Multiple chunks |\n| Unused code | Low coverage |\n| Missing splits | Single large chunk |\n\n### Optimization Actions\n\n| Finding | Action |\n|---------|--------|\n| Big library | Import specific modules |\n| Duplicate deps | Dedupe, update versions |\n| Route in main | Code split |\n| Unused exports | Tree shake |\n\n---\n\n## 4. Runtime Profiling\n\n### Performance Tab Analysis\n\n| Pattern | Meaning |\n|---------|---------|\n| Long tasks (>50ms) | UI blocking |\n| Many small tasks | Possible batching opportunity |\n| Layout/paint | Rendering bottleneck |\n| Script | JavaScript execution |\n\n### Memory Tab Analysis\n\n| Pattern | Meaning |\n|---------|---------|\n| Growing heap | Possible leak |\n| Large retained | Check references |\n| Detached DOM | Not cleaned up |\n\n---\n\n## 5. Common Bottlenecks\n\n### By Symptom\n\n| Symptom | Likely Cause |\n|---------|--------------|\n| Slow initial load | Large JS, render blocking |\n| Slow interactions | Heavy event handlers |\n| Jank during scroll | Layout thrashing |\n| Growing memory | Leaks, retained refs |\n\n---\n\n## 6. Quick Win Priorities\n\n| Priority | Action | Impact |\n|----------|--------|--------|\n| 1 | Enable compression | High |\n| 2 | Lazy load images | High |\n| 3 | Code split routes | High |\n| 4 | Cache static assets | Medium |\n| 5 | Optimize images | Medium |\n\n---\n\n## 7. Anti-Patterns\n\n| ❌ Don't | ✅ Do |\n|----------|-------|\n| Guess at problems | Profile first |\n| Micro-optimize | Fix biggest issue |\n| Optimize early | Optimize when needed |\n| Ignore real users | Use RUM data |\n\n---\n\n> **Remember:** The fastest code is code that doesn't run. Remove before optimizing.\n\n## When to Use\nThis skill is applicable to execute the workflow or actions described in the overview.\n\n## Limitations\n- Use this skill only when the task clearly matches the scope described above.\n- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.\n- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are 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