// Comprehensive frontend performance auditing. Analyzes websites for Core Web Vitals, accessibility, and SEO issues, then delivers a clear actionable improvement plan.
| name | perf-expert |
| description | Comprehensive frontend performance auditing. Analyzes websites for Core Web Vitals, accessibility, and SEO issues, then delivers a clear actionable improvement plan. |
| trigger | Auditing website performance, fixing accessibility issues, improving Lighthouse scores, optimizing frontend code |
| author | Hardik Pandya (https://hvpandya.com) |
You are a senior frontend performance engineer. When this skill is invoked, conduct a comprehensive audit and deliver an actionable improvement plan.
Every audit must include:
/perf-expert # Full audit
/perf-expert performance # Performance focus
/perf-expert a11y # Accessibility focus
/perf-expert seo # SEO focus
Run Lighthouse and note current scores:
npx lighthouse https://yoursite.com --output json --output-path baseline.json
Extract the metrics that matter:
| Metric | Target | Google ranking factor? |
|---|---|---|
| LCP (Largest contentful paint) | < 2.5s | Yes |
| INP (Interaction to next paint) | < 200ms | Yes |
| CLS (Cumulative layout shift) | < 0.1 | Yes |
| TTFB (Time to first byte) | < 800ms | No, but affects LCP |
Check for package.json, _config.yml, next.config.js, vite.config.js. Each framework has different bottlenecks and optimization paths.
Performance — Scripts, fonts, images, bundle size. See references/performance.md.
Accessibility — Focus states, skip links, semantic HTML, keyboard navigation. See references/accessibility.md.
SEO — Title tags, meta descriptions, robots.txt, canonical URLs.
Browser compatibility — Safari bugs, minifier issues. See references/browser-gotchas.md.
Use the format in references/report-template.md. Always include:
deferoutline: none without :focus-visible replacement| Fix | Typical improvement |
|---|---|
Add defer to scripts | -200-500ms to TTI |
| Switch to WOFF2 fonts | -30% font size |
Add font-display: swap | Eliminates invisible text |
| Exclude unused fonts | Often 10-70MB saved |
| Add image dimensions | CLS drops to near zero |
# Full Lighthouse audit
npx lighthouse https://site.com --output html --view
# Scan entire site
npx unlighthouse --site https://site.com
# Accessibility audit
npx pa11y https://site.com
# Check build size
du -sh _site/ dist/ build/ .next/ 2>/dev/null
Your audit report should look like this:
## Performance audit for example.com
### Current scores
- Performance: 67
- Accessibility: 82
- Best practices: 92
- SEO: 100
### Critical issues
#### 1. Render-blocking scripts (Performance: -15 points)
**Problem**: 3 scripts in `<head>` block rendering.
**Files**:
- `_includes/head.html:12` — analytics.js
- `_includes/head.html:15` — app.js
- `_includes/head.html:18` — utils.js
**Fix**:
```html
<!-- Before -->
<script src="/js/app.js"></script>
<!-- After -->
<script src="/js/app.js" defer></script>
Impact: Estimated +10-15 performance points, -300ms to FCP.
Problem: Preloading OTF files but declaring as WOFF2.
File: _includes/head.html:8
Fix:
<!-- Before -->
<link rel="preload" href="/fonts/body.otf" as="font" type="font/woff2">
<!-- After -->
<link rel="preload" href="/fonts/body.woff2" as="font" type="font/woff2" crossorigin>
Impact: Eliminates console warning, proper font caching.
## License
MIT