benchmark-perf

name	benchmark-perf
description	Performance Benchmarking Skill: Measures page load times, resource sizes, and detects regressions. MANDATORY TRIGGERS: performance, benchmark, perf, page speed, load time, Core Web Vitals, slow, regression.
argument-hint	<page URL or feature to benchmark>

Bobby Performance Skill

Measures page load times, resource sizes, and detects regressions. Establishes baselines and compares before/after on every run.

Before Starting

1. Check learnings — Read .claude/skills/bobby-performance/learnings.md + .claude/skills/bobby-performance/learnings.local.md
2. Read .bobby/benchmarks/baseline.json if it exists
3. Health check — Verify dev environment:

Benchmarking Process

Step 1: Identify Pages to Benchmark

Benchmark these pages (in order of priority):

1. Homepage / landing page
2. Main dashboard or primary user view
3. Any pages affected by recently shipped tickets
4. Pages listed in .bobbyrc.yml under watchdog_pages (if configured)

Step 2: Measure Each Page

For each page, measure via browser automation:

Page Load Metrics:

• Time to First Byte (TTFB) — performance.timing.responseStart - performance.timing.requestStart
• First Contentful Paint (FCP) — performance.getEntriesByName('first-contentful-paint')[0].startTime
• DOM Content Loaded — performance.timing.domContentLoadedEventEnd - performance.timing.navigationStart
• Full Page Load — performance.timing.loadEventEnd - performance.timing.navigationStart

Resource Metrics:

• Total transfer size — sum of performance.getEntriesByType('resource').map(r => r.transferSize)
• Number of requests — performance.getEntriesByType('resource').length
• Largest resource — identify the biggest JS/CSS/image file

Interaction Metrics (if applicable):

• Time to Interactive — can the user click/type within 3 seconds?
• Layout shift — does the page jump around during load?

Step 3: Record Results

Save results to .bobby/benchmarks/run-{YYYYMMDD-HHmmss}.json:

{
  "timestamp": "ISO date",
  "branch": "current git branch",
  "pages": [
    {
      "url": "/dashboard",
      "ttfb_ms": 120,
      "fcp_ms": 450,
      "dom_loaded_ms": 800,
      "full_load_ms": 1200,
      "total_transfer_kb": 850,
      "request_count": 42,
      "largest_resource": { "url": "/js/bundle.js", "size_kb": 320 }
    }
  ]
}

Step 4: Compare to Baseline

<comparison_rules> If a baseline exists (.bobby/benchmarks/baseline.json):

Metric	Regression Threshold	Action
TTFB	>20% slower	Flag as warning
FCP	>15% slower	Flag as warning
Full Load	>10% slower	Flag as regression
Transfer Size	>15% larger	Flag as warning
Request Count	>20% more	Flag as warning

Regression = critical issue that should block shipping Warning = worth investigating but not blocking

If no baseline exists, save current results as .bobby/benchmarks/baseline.json. </comparison_rules>

Completing Work

1. Save benchmark results to .bobby/benchmarks/
2. If this is the first run, also save as baseline.json
3. Output a summary table:

Performance Report — {date}
Branch: {branch}

| Page | TTFB | FCP | Load | Size | Requests | Status |
|------|------|-----|------|------|----------|--------|
| /dashboard | 120ms | 450ms | 1.2s | 850KB | 42 | ✓ OK |
| /settings | 200ms (+40%) | ... | ... | ... | ... | ⚠ TTFB regression |

4. If regressions found: bobby ticket create -t "PERF: {page} load time regressed {%}" --type bug -p high
5. If you discovered a pattern: bobby learn bobby-performance "pattern" "description"

---

Project overrides

If .claude/skills/bobby-performance/SKILL.local.md exists, read it and follow it. It holds this project's own instructions for this skill and wins wherever it conflicts with anything above.

SKILL.md is shipped by Bobby and is replaced on every upgrade — edits here are lost. SKILL.local.md is yours and is never overwritten.