perf-web-optimization
The perf-web-optimization Claude Code skill provides a systematic approach to improving web performance across bundle size, image optimization, lazy loading, and caching strategies. Use this skill when addressing slow sites, reducing bundle sizes, fixing layout shifts, optimizing Time to Interactive, or improving Lighthouse scores, but not for Core Web Vitals-specific fixes, running Lighthouse audits, or Astro-specific optimization.
git clone --depth 1 https://github.com/tech-leads-club/agent-skills /tmp/perf-web-optimization && cp -r /tmp/perf-web-optimization/packages/skills-catalog/skills/(performance)/perf-web-optimization ~/.claude/skills/perf-web-optimizationSKILL.md
# Web Performance Optimization
Systematic approach: Measure → Identify → Prioritize → Implement → Verify.
## Target Metrics
| Metric | Good | Needs Work | Poor |
| ------ | ------- | ---------- | ------- |
| LCP | < 2.5s | 2.5-4s | > 4s |
| INP | < 200ms | 200-500ms | > 500ms |
| CLS | < 0.1 | 0.1-0.25 | > 0.25 |
| TTFB | < 800ms | 800ms-1.8s | > 1.8s |
## Quick Wins
### 1. Images (usually biggest impact on LCP)
```html
<!-- Hero/LCP image: eager + high priority -->
<img src="/hero.webp" alt="Hero" width="1200" height="600" loading="eager" fetchpriority="high" decoding="async" />
<!-- Below fold: lazy load -->
<img src="/product.webp" alt="Product" width="400" height="300" loading="lazy" decoding="async" />
```
Always set `width` and `height` to prevent CLS.
### 2. Fonts (common LCP/CLS culprit)
```html
<!-- Preconnect to font origin -->
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
<!-- Non-blocking font load -->
<link
rel="stylesheet"
href="https://fonts.googleapis.com/css2?family=Inter&display=swap"
media="print"
onload="this.media='all'"
/>
```
### 3. Third-party Scripts (common INP killer)
```html
<!-- Defer to user interaction -->
<script>
function loadThirdParty() {
// Load analytics, chat widgets, etc.
}
;['scroll', 'click', 'touchstart'].forEach((e) => addEventListener(e, loadThirdParty, { once: true, passive: true }))
setTimeout(loadThirdParty, 5000)
</script>
```
### 4. Critical CSS
Inline critical CSS in `<head>`, defer the rest:
```html
<style>
/* critical styles */
</style>
<link rel="preload" href="/styles.css" as="style" onload="this.rel='stylesheet'" />
```
## Bundle Analysis
```bash
# Webpack
npx webpack-bundle-analyzer dist/stats.json
# Vite
npx vite-bundle-visualizer
# Check package size before installing
npx bundlephobia <package-name>
```
Common heavy packages to replace:
- `moment` (67KB) → `date-fns` (12KB) or `dayjs` (2KB)
- `lodash` (72KB) → cherry-pick imports or native methods
## Code Splitting Patterns
```javascript
// React lazy
const Chart = lazy(() => import('./Chart'))
// Next.js dynamic
const Admin = dynamic(() => import('./Admin'), { ssr: false })
// Vite/Rollup manual chunks
build: {
rollupOptions: {
output: {
manualChunks: {
vendor: ['react', 'react-dom']
}
}
}
}
```
## Caching Headers
```
# Static assets (immutable hash in filename)
Cache-Control: public, max-age=31536000, immutable
# HTML (revalidate)
Cache-Control: no-cache
# API responses
Cache-Control: private, max-age=0, must-revalidate
```
## Measurement
For running audits, reading reports, and setting budgets, use the **perf-lighthouse** skill.
## Checklist
### Images
- [ ] Modern formats (WebP/AVIF)
- [ ] Responsive `srcset`
- [ ] `width`/`height` attributes
- [ ] `loading="lazy"` below fold
- [ ] `fetchpriority="high"` on LCP image
### JavaScript
- [ ] Bundle < 200KB gzipped
- [ ] Code splitting by route
- [ ] Third-party scripts deferred
- [ ] No unused dependencies
### CSS
- [ ] Critical CSS inlined
- [ ] Non-critical CSS deferred
- [ ] No unused CSS
### Fonts
- [ ] `font-display: swap`
- [ ] Preconnect to font origin
- [ ] Subset if possible
## Detailed Examples
For in-depth optimization patterns, see:
- [references/core-web-vitals.md](references/core-web-vitals.md) - Fixing LCP, CLS, INP issues
- [references/bundle-optimization.md](references/bundle-optimization.md) - Reducing JS bundle size
- [references/image-optimization.md](references/image-optimization.md) - Image formats, responsive images, sharp scriptsAudit and improve web accessibility following WCAG 2.1 guidelines. Use when asked to "improve accessibility", "a11y audit", "WCAG compliance", "screen reader support", "keyboard navigation", or "make accessible". Do NOT use for SEO (use seo), performance (use core-web-vitals), or comprehensive site audits covering multiple areas (use web-quality-audit).
When the user wants to build an AI-powered outreach system, write cold emails, improve deliverability, or scale personalized outreach. Also use when the user mentions 'cold email,' 'cold outreach,' 'outreach automation,' 'Instantly,' 'Smartlead,' 'Clay,' 'email sequences,' 'deliverability,' 'personalization at scale,' 'reply rate,' or 'outreach stack.' This skill covers the complete AI cold outreach system from signal detection through conversion. Do NOT use for technical implementation, code review, or software architecture.
When the user wants to price an AI product, choose a charge metric, design pricing tiers, or optimize margins. Also use when the user mentions 'AI pricing,' 'usage-based pricing,' 'consumption pricing,' 'outcome pricing,' 'BYOK,' 'bring your own key,' 'per-seat pricing,' 'pricing tiers,' 'AI margins,' 'cost per token,' or 'pricing model.' This skill covers pricing strategy, packaging, and margin management for AI-native products. Do NOT use for technical implementation, code review, or software architecture.
When the user wants to deploy AI sales development reps, automate sales qualification, build signal-to-action routing, or design AI agent architecture for sales. Also use when the user mentions 'AI SDR,' 'AI sales agent,' 'automated qualification,' 'signal routing,' 'sales automation,' '11x,' 'Artisan,' 'AiSDR,' 'AI BDR,' or 'autonomous sales.' This skill covers AI SDR deployment, qualification automation, and agent architecture for sales development. Do NOT use for technical implementation, code review, or software architecture.
When the user wants to build programmatic SEO with AI, create competitor alternative pages, optimize for AI Overviews, or scale content production. Also use when the user mentions 'SEO,' 'programmatic SEO,' 'AI content,' 'competitor alternative pages,' 'AI Overviews,' 'search optimization,' 'DataForSEO,' 'content at scale,' 'keyword strategy,' or 'organic traffic.' This skill covers AI-powered SEO strategy from keyword research through programmatic page generation. Do NOT use for technical implementation, code review, or software architecture.
When the user wants to create UGC ad campaigns, recruit UGC creators, generate AI UGC content, or scale with user-generated content. Also use when the user mentions 'UGC,' 'user-generated content,' 'creator ads,' 'Spark Ads,' 'whitelisting,' 'AI UGC,' 'Arcads,' 'Creatify,' 'creator brief,' or 'UGC testing.' This skill covers the UGC growth framework from creator recruitment through AI-powered scaling. Do NOT use for technical implementation, code review, or software architecture.
Expert AWS Cloud Advisor for architecture design, security review, and implementation guidance. Leverages AWS MCP tools for accurate, documentation-backed answers. Use when user asks about AWS architecture, security, service selection, migrations, troubleshooting, or learning AWS. Triggers on AWS, Lambda, S3, EC2, ECS, EKS, DynamoDB, RDS, CloudFormation, CDK, Terraform, Serverless, SAM, IAM, VPC, API Gateway, or any AWS service. Do NOT use for non-AWS cloud providers or general infrastructure without AWS context.
Apply modern web development best practices for security, compatibility, and code quality. Use when asked to "apply best practices", "security audit", "modernize code", "code quality review", or "check for vulnerabilities". Do NOT use for accessibility (use web-accessibility), SEO (use seo), performance (use core-web-vitals), or comprehensive multi-area audits (use web-quality-audit).