Web Perf Audit

Web Performance Audit

Systematically measure and improve web performance using bundled scripts and reference docs.

When to activate

• User asks to improve page speed, Core Web Vitals, or Lighthouse scores
• Before a production launch or after a large frontend change
• When investigating LCP, INP, CLS, TBT, or bundle size regressions

Workflow

1. Baseline — Run scripts/collect-metrics.sh against the target URL (or use DevTools if unavailable).
2. Compare — Load references/core-web-vitals.md and references/thresholds.md to classify pass/advisory/fail.
3. Diagnose — Identify top offenders: render-blocking CSS/JS, large images, layout shifts, long tasks.
4. Recommend — Produce a prioritized fix list with estimated impact (high/medium/low).
5. Verify — Re-run metrics after changes; report delta vs baseline.

Progressive disclosure

• Start with discovery metadata only until the user confirms a URL or repo.
• Load references/core-web-vitals.md when explaining metric definitions.
• Run scripts only when the user wants automated collection.

Output template

## Performance audit — {url}

| Metric | Value | Rating |
|--------|-------|--------|
| LCP    | …     | …      |
| INP    | …     | …      |
| CLS    | …     | …      |

### Top issues
1. …
2. …

### Recommended fixes
1. …

Safety

• Do not run audits against URLs the user does not own without permission.
• Scripts are read-only against public URLs; they do not modify remote systems.
• Redact auth tokens and cookies from any logged output.

Bundled resources

• scripts/collect-metrics.sh — fetch timing headers and basic vitals proxies
• scripts/parse-har-summary.js — summarize a HAR export if provided
• references/core-web-vitals.md — metric definitions
• references/thresholds.md — good / needs improvement / poor bands