Agent skill
perf
Performance profiling and optimization. Use for benchmarking code, analyzing performance, running Lighthouse audits, and finding hotspots.
Install this agent skill to your Project
npx add-skill https://github.com/johnlindquist/claude/tree/main/skills/perf
SKILL.md
Performance Profiler
Profile, benchmark, and optimize code performance.
Prerequisites
# Node.js for profiling
node --version
# Lighthouse for web perf
npm install -g lighthouse
# Gemini for analysis
pip install google-generativeai
export GEMINI_API_KEY=your_api_key
Benchmarking
Quick Benchmark
# Time a Node.js script
time node script.js
# With memory
/usr/bin/time -l node script.js # macOS
/usr/bin/time -v node script.js # Linux
Node.js Performance Hooks
// benchmark.js
const { performance, PerformanceObserver } = require('perf_hooks');
const obs = new PerformanceObserver((list) => {
console.log(list.getEntries()[0].duration);
});
obs.observe({ entryTypes: ['measure'] });
performance.mark('start');
// Code to benchmark
yourFunction();
performance.mark('end');
performance.measure('duration', 'start', 'end');
Console Timing
console.time('operation');
// Code to time
console.timeEnd('operation'); // Prints: operation: 123.456ms
Node.js Profiling
V8 Profiler
# Generate profile
node --prof script.js
# Process the log
node --prof-process isolate-*.log > profile.txt
Inspect Mode
# Start with inspector
node --inspect script.js
# Break on start
node --inspect-brk script.js
# Open Chrome DevTools
open chrome://inspect
Memory Profiling
# Heap snapshot
node --heapsnapshot-signal=SIGUSR2 script.js
# Then: kill -USR2 <pid>
# Expose GC for testing
node --expose-gc script.js
Lighthouse Audits
Basic Audit
# Full audit
lighthouse https://example.com
# Output to JSON
lighthouse https://example.com --output=json --output-path=report.json
# Output to HTML
lighthouse https://example.com --output=html --output-path=report.html
# Specific categories
lighthouse https://example.com --only-categories=performance
# Mobile vs Desktop
lighthouse https://example.com --preset=desktop
lighthouse https://example.com --preset=mobile # default
Performance Only
lighthouse https://example.com \
--only-categories=performance \
--output=json \
--output-path=perf-report.json
Chrome Flags
# Headless
lighthouse https://example.com --chrome-flags="--headless"
# Custom viewport
lighthouse https://example.com --chrome-flags="--window-size=1920,1080"
AI Performance Analysis
Analyze Code for Performance
CODE=$(cat slow-function.ts)
gemini -m pro -o text -e "" "Analyze this code for performance issues:
$CODE
Identify:
1. Time complexity issues
2. Memory leaks or bloat
3. Unnecessary operations
4. Opportunities for optimization
5. Caching opportunities
Provide specific recommendations with code examples."
Analyze Profile Output
PROFILE=$(cat profile.txt)
gemini -m pro -o text -e "" "Analyze this Node.js profile:
$PROFILE
Identify:
1. Hot functions (most time spent)
2. Potential bottlenecks
3. Optimization opportunities
4. Priority of fixes"
Finding Hotspots
CPU Hotspots
# Record CPU profile
node --cpu-prof script.js
# Analyze generated .cpuprofile
# Open in Chrome DevTools or use:
npx speedscope *.cpuprofile
Memory Hotspots
# Find large objects
node --heapsnapshot-signal=SIGUSR2 app.js
# Use clinic.js
npx clinic doctor -- node script.js
npx clinic flame -- node script.js
npx clinic bubbleprof -- node script.js
Bundle Analysis
# Webpack
npx webpack-bundle-analyzer stats.json
# Vite
npx vite build --report
# Generic
du -sh dist/*
ls -lhS dist/*.js
Common Patterns
Anti-Patterns to Check
gemini -m pro -o text -e "" "Check this code for common performance anti-patterns:
$(cat src/*.ts)
Look for:
- Synchronous I/O in hot paths
- Repeated DOM queries
- Unnecessary re-renders
- N+1 query patterns
- Memory leaks in closures
- Blocking the event loop"
Optimization Checklist
gemini -m pro -o text -e "" "Create a performance optimization checklist for:
Application type: [web app / API / CLI]
Stack: [your stack]
Current issues: [symptoms]
Include priority order and estimated impact."
Comparison Benchmarks
Before/After
#!/bin/bash
# benchmark-compare.sh
echo "=== Before optimization ==="
git checkout main
npm install
time npm run benchmark
echo "=== After optimization ==="
git checkout optimization-branch
npm install
time npm run benchmark
A/B Script
#!/bin/bash
# Run same benchmark multiple times
for i in {1..10}; do
echo "Run $i:"
node benchmark.js
done | tee results.txt
# Calculate average
grep "time:" results.txt | awk '{sum+=$2; n++} END {print "Average:", sum/n}'
Best Practices
- Measure first - Don't optimize without data
- Profile production - Dev performance differs
- Automate benchmarks - Track over time
- Focus on hot paths - 80/20 rule
- Test on target devices - Especially mobile
- Monitor after deploy - Verify improvements
- Document baselines - Know what "good" looks like
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