claudekit/skills/performance-optimization/references/profiling.md

Profiling Tools Reference

Python

cProfile (built-in, function-level)

python -m cProfile -o output.prof script.py
# Visualize
pip install snakeviz && snakeviz output.prof

py-spy (sampling, production-safe)

# Top-like view of running process
py-spy top --pid 12345

# Generate flame graph
py-spy record -o profile.svg --pid 12345

line_profiler (line-by-line)

# Add @profile decorator to target function
kernprof -lv script.py

memory_profiler (memory usage)

# Add @profile decorator
python -m memory_profiler script.py

# Or use stdlib tracemalloc for snapshot comparison

Scalene (CPU + memory + GPU)

scalene script.py
# Modern alternative, AI-suggested optimizations

JavaScript / TypeScript

Chrome DevTools Performance

• Performance tab → Record → interact → Stop
• Flame chart shows main thread activity
• Look for long tasks (>50ms), layout thrashing

Lighthouse (web vitals)

npx lighthouse https://localhost:3000 --output=json
# CI integration
npx @lhci/cli autorun

Bundle Analysis

# Webpack
npx webpack-bundle-analyzer stats.json

# Next.js
ANALYZE=true next build

# Source map explorer
npx source-map-explorer dist/**/*.js

clinic.js (Node.js)

# Event loop health
clinic doctor -- node app.js

# CPU flame graph
clinic flame -- node app.js

# Async bottlenecks
clinic bubbleprof -- node app.js

Node.js built-in

node --prof app.js
node --prof-process isolate-*.log > profile.txt

Benchmarking

Python

# pytest-benchmark
pytest --benchmark-only

# timeit
python -m timeit -s "setup" "expression"

JavaScript/TypeScript

// Vitest bench (built-in)
// my-func.bench.ts
import { bench } from 'vitest';

bench('my function', () => {
  myFunction(testData);
});

npx vitest bench