benchmark

What this skill does

When applied, it prepends a system prompt before your request is sent — no extra calls and no change to how you are billed beyond the added tokens.

---
name: benchmark
description: Use this skill to measure performance baselines, detect regressions before/after PRs, and compare stack alternatives.
origin: ECC
---

# Benchmark — Performance Baseline & Regression Detection

## When to Use

- Before and after a PR to measure performance impact
- Setting up performance baselines for a project
- When users report "it feels slow"
- Before a launch — ensure you meet performance targets
- Comparing your stack against alternatives

## How It Works

### Mode 1: Page Performance

Measures real browser metrics via browser MCP:

```
1. Navigate to each target URL
2. Measure Core Web Vitals:
   - LCP (Largest Contentful Paint) — target < 2.5s
   - CLS (Cumulative Layout Shift) — target < 0.1
   - INP (Interaction to Next Paint) — target < 200ms
   - FCP (First Contentful Paint) — target < 1.8s
   - TTFB (Time to First Byte) — target < 800ms
3. Measure resource sizes:
   - Total page weight (target < 1MB)
   - JS bundle size (target < 200KB gzipped)
   - CSS size
   - Image weight
   - Third-party script weight
4. Count network requests
5. Check for render-blocking resources
```

### Mode 2: API Performance

Benchmarks API endpoints:

```
1. Hit each endpoint 100 times
2. Measure: p50, p95, p99 latency
3. Track: response size, status codes
4. Test under load: 10 concurrent requests
5. Compare against SLA targets
```

### Mode 3: Build Performance

Measures development feedback loop:

```
1. Cold build time
2. Hot reload time (HMR)
3. Test suite duration
4. TypeScript check time
5. Lint time
6. Docker build time
```

### Mode 4: Before/After Comparison

Run before and after a change to measure impact:

```
/benchmark baseline    # saves current metrics
# ... make changes ...
/benchmark compare     # compares against baseline
```

Output:
```
| Metric | Before | After | Delta | Verdict |
|--------|--------|-------|-------|---------|
| LCP | 1.2s | 1.4s | +200ms | WARNING: WARN |
| Bundle | 180KB | 175KB | -5KB | ✓ BETTER |
| Bu

Use this skill

{
  "model": "gpt-4o-mini",
  "skill": "imp-748bffcd-be7b-40fe-be22-c5d389c16296",
  "messages": [{ "role": "user", "content": "…" }]
}

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