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performance-profiling

Performance profiling principles. Measurement, analysis, and optimization techniques.

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6 Oct 2026
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Get it through your agent npx skills add sickn33/agentic-awesome-skills@performance-profiling

Skill instructions

Rendered from the published SKILL.md, 146 lines.

Performance Profiling

Measure, analyze, optimize - in that order.

🔧 Runtime Scripts

Inspect this bundled helper as code before use and run only against an authorized URL. Lighthouse launches a browser and can load third-party resources; lab scores do not establish field Core Web Vitals. The helper reports command/JSON failures and unavailable scores separately; inspect the returned error and do not treat an unavailable category as a zero score.

Script Purpose Usage
scripts/lighthouse_audit.py Lighthouse performance audit python scripts/lighthouse_audit.py https://example.com

1. Core Web Vitals

Targets

Metric Good Poor Measures
LCP < 2.5s > 4.0s Loading
INP < 200ms > 500ms Interactivity
CLS < 0.1 > 0.25 Stability

When to Measure

Stage Tool
Development Local Lighthouse
CI/CD Lighthouse CI
Production RUM (Real User Monitoring)

2. Profiling Workflow

The 4-Step Process

1. BASELINE → Measure current state
2. IDENTIFY → Find the bottleneck
3. FIX → Make targeted change
4. VALIDATE → Confirm improvement

Profiling Tool Selection

Problem Tool
Page load Lighthouse
Bundle size Bundle analyzer
Runtime DevTools Performance
Memory DevTools Memory
Network DevTools Network

3. Bundle Analysis

What to Look For

Issue Indicator
Large dependencies Top of bundle
Duplicate code Multiple chunks
Unused code Low coverage
Missing splits Single large chunk

Optimization Actions

Finding Action
Big library Import specific modules
Duplicate deps Dedupe, update versions
Route in main Code split
Unused exports Tree shake

4. Runtime Profiling

Performance Tab Analysis

Pattern Meaning
Long tasks (>50ms) UI blocking
Many small tasks Possible batching opportunity
Layout/paint Rendering bottleneck
Script JavaScript execution

Memory Tab Analysis

Pattern Meaning
Growing heap Possible leak
Large retained Check references
Detached DOM Not cleaned up

5. Common Bottlenecks

By Symptom

Symptom Likely Cause
Slow initial load Large JS, render blocking
Slow interactions Heavy event handlers
Jank during scroll Layout thrashing
Growing memory Leaks, retained refs

6. Quick Win Priorities

Priority Action Impact
1 Enable compression High
2 Lazy load offscreen images; keep the LCP image eager Workload-dependent
3 Code split routes High
Show the whole skill (26 more lines)

| 4 | Cache static assets | Medium | | 5 | Optimize images | Medium |

7. Anti-Patterns

❌ Don't ✅ Do
Guess at problems Profile first
Micro-optimize Fix biggest issue
Optimize early Optimize when needed
Ignore real users Use RUM data

Remember: The fastest code is code that doesn't run. Remove before optimizing.

When to Use

This skill is applicable to execute the workflow or actions described in the overview.

Limitations

  • Use this skill only when the task clearly matches the scope described above.
  • Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
  • Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.