---
name: web-performance-optimization
description: "Web Performance Optimization workflow skill. Use this skill when the user needs Optimize website and web application performance including loading speed, Core Web Vitals, bundle size, caching strategies, and runtime performance and the operator should preserve the upstream workflow, copied support files, and provenance before merging or handing off."
version: "0.0.1"
category: fullstack-web
tags: ["web-performance-optimization", "optimize", "website", "and", "web", "application", "performance", "including"]
complexity: advanced
risk: caution
tools: ["codex-cli", "claude-code", "cursor", "gemini-cli", "opencode"]
source: community
author: "sickn33"
date_added: "2026-04-15"
date_updated: "2026-04-25"
---

# Web Performance Optimization

## Overview

This public intake copy packages `plugins/antigravity-awesome-skills-claude/skills/web-performance-optimization` from `https://github.com/sickn33/antigravity-awesome-skills` into the native Omni Skills editorial shape without hiding its origin.

Use it when the operator needs the upstream workflow, support files, and repository context to stay intact while the public validator and private enhancer continue their normal downstream flow.

This intake keeps the copied upstream files intact and uses the `external_source` block in `metadata.json` plus `ORIGIN.md` as the provenance anchor for review.

# Web Performance Optimization

Imported source sections that did not map cleanly to the public headings are still preserved below or in the support files. Notable imported sections: How It Works, Performance Audit Results, Bundle Size Optimization, Image Optimization, Common Pitfalls, Performance Checklist.

## When to Use This Skill

Use this section as the trigger filter. It should make the activation boundary explicit before the operator loads files, runs commands, or opens a pull request.

- Use when website or app is loading slowly
- Use when optimizing for Core Web Vitals (LCP, FID, CLS)
- Use when reducing JavaScript bundle size
- Use when improving Time to Interactive (TTI)
- Use when optimizing images and assets
- Use when implementing caching strategies

## Operating Table

| Situation | Start here | Why it matters |
| --- | --- | --- |
| First-time use | `metadata.json` | Confirms repository, branch, commit, and imported path through the `external_source` block before touching the copied workflow |
| Provenance review | `ORIGIN.md` | Gives reviewers a plain-language audit trail for the imported source |
| Workflow execution | `SKILL.md` | Starts with the smallest copied file that materially changes execution |
| Supporting context | `SKILL.md` | Adds the next most relevant copied source file without loading the entire package |
| Handoff decision | `## Related Skills` | Helps the operator switch to a stronger native skill when the task drifts |

## Workflow

This workflow is intentionally editorial and operational at the same time. It keeps the imported source useful to the operator while still satisfying the public intake standards that feed the downstream enhancer flow.

1. Confirm the user goal, the scope of the imported workflow, and whether this skill is still the right router for the task.
2. Read the overview and provenance files before loading any copied upstream support files.
3. Load only the references, examples, prompts, or scripts that materially change the outcome for the current request.
4. Execute the upstream workflow while keeping provenance and source boundaries explicit in the working notes.
5. Validate the result against the upstream expectations and the evidence you can point to in the copied files.
6. Escalate or hand off to a related skill when the work moves out of this imported workflow's center of gravity.
7. Before merge or closure, record what was used, what changed, and what the reviewer still needs to verify.

### Imported Workflow Notes

#### Imported: Overview

Help developers optimize website and web application performance to improve user experience, SEO rankings, and conversion rates. This skill provides systematic approaches to measure, analyze, and improve loading speed, runtime performance, and Core Web Vitals metrics.

#### Imported: How It Works

### Step 1: Measure Current Performance

I'll help you establish baseline metrics:
- Run Lighthouse audits
- Measure Core Web Vitals (LCP, FID, CLS)
- Check bundle sizes
- Analyze network waterfall
- Identify performance bottlenecks

### Step 2: Identify Issues

Analyze performance problems:
- Large JavaScript bundles
- Unoptimized images
- Render-blocking resources
- Slow server response times
- Missing caching headers
- Layout shifts
- Long tasks blocking main thread

### Step 3: Prioritize Optimizations

Focus on high-impact improvements:
- Critical rendering path optimization
- Code splitting and lazy loading
- Image optimization
- Caching strategies
- Third-party script optimization

### Step 4: Implement Optimizations

Apply performance improvements:
- Optimize assets (images, fonts, CSS, JS)
- Implement code splitting
- Add caching headers
- Lazy load non-critical resources
- Optimize critical rendering path

### Step 5: Verify Improvements

Measure impact of changes:
- Re-run Lighthouse audits
- Compare before/after metrics
- Monitor real user metrics (RUM)
- Test on different devices and networks

## Examples

### Example 1: Ask for the upstream workflow directly

```text
Use @web-performance-optimization to handle <task>. Start from the copied upstream workflow, load only the files that change the outcome, and keep provenance visible in the answer.
```

**Explanation:** This is the safest starting point when the operator needs the imported workflow, but not the entire repository.

### Example 2: Ask for a provenance-grounded review

```text
Review @web-performance-optimization against metadata.json and ORIGIN.md, then explain which copied upstream files you would load first and why.
```

**Explanation:** Use this before review or troubleshooting when you need a precise, auditable explanation of origin and file selection.

### Example 3: Narrow the copied support files before execution

```text
Use @web-performance-optimization for <task>. Load only the copied references, examples, or scripts that change the outcome, and name the files explicitly before proceeding.
```

**Explanation:** This keeps the skill aligned with progressive disclosure instead of loading the whole copied package by default.

### Example 4: Build a reviewer packet

```text
Review @web-performance-optimization using the copied upstream files plus provenance, then summarize any gaps before merge.
```

**Explanation:** This is useful when the PR is waiting for human review and you want a repeatable audit packet.

### Imported Usage Notes

#### Imported: Examples

### Example 1: Optimizing Core Web Vitals

```markdown

## Best Practices

Treat the generated public skill as a reviewable packaging layer around the upstream repository. The goal is to keep provenance explicit and load only the copied source material that materially improves execution.

- Measure First - Always establish baseline metrics before optimizing
- Use Lighthouse - Run audits regularly to track progress
- Optimize Images - Use modern formats (WebP, AVIF) and responsive images
- Code Split - Break large bundles into smaller chunks
- Lazy Load - Defer non-critical resources
- Cache Aggressively - Set proper cache headers for static assets
- Minimize Main Thread Work - Keep JavaScript execution under 50ms chunks

### Imported Operating Notes

#### Imported: Best Practices

### ✅ Do This

- **Measure First** - Always establish baseline metrics before optimizing
- **Use Lighthouse** - Run audits regularly to track progress
- **Optimize Images** - Use modern formats (WebP, AVIF) and responsive images
- **Code Split** - Break large bundles into smaller chunks
- **Lazy Load** - Defer non-critical resources
- **Cache Aggressively** - Set proper cache headers for static assets
- **Minimize Main Thread Work** - Keep JavaScript execution under 50ms chunks
- **Preload Critical Resources** - Use `<link rel="preload">` for critical assets
- **Use CDN** - Serve static assets from CDN for faster delivery
- **Monitor Real Users** - Track Core Web Vitals from real users

### ❌ Don't Do This

- **Don't Optimize Blindly** - Measure first, then optimize
- **Don't Ignore Mobile** - Test on real mobile devices and slow networks
- **Don't Block Rendering** - Avoid render-blocking CSS and JavaScript
- **Don't Load Everything Upfront** - Lazy load non-critical resources
- **Don't Forget Dimensions** - Always specify image width/height
- **Don't Use Synchronous Scripts** - Use async or defer attributes
- **Don't Ignore Third-Party Scripts** - They often cause performance issues
- **Don't Skip Compression** - Always compress and minify assets

## Troubleshooting

### Problem: The operator skipped the imported context and answered too generically

**Symptoms:** The result ignores the upstream workflow in `plugins/antigravity-awesome-skills-claude/skills/web-performance-optimization`, fails to mention provenance, or does not use any copied source files at all.
**Solution:** Re-open `metadata.json`, `ORIGIN.md`, and the most relevant copied upstream files. Check the `external_source` block first, then restate the provenance before continuing.

### Problem: The imported workflow feels incomplete during review

**Symptoms:** Reviewers can see the generated `SKILL.md`, but they cannot quickly tell which references, examples, or scripts matter for the current task.
**Solution:** Point at the exact copied references, examples, scripts, or assets that justify the path you took. If the gap is still real, record it in the PR instead of hiding it.

### Problem: The task drifted into a different specialization

**Symptoms:** The imported skill starts in the right place, but the work turns into debugging, architecture, design, security, or release orchestration that a native skill handles better.
**Solution:** Use the related skills section to hand off deliberately. Keep the imported provenance visible so the next skill inherits the right context instead of starting blind.



## Related Skills

- `@00-andruia-consultant` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@00-andruia-consultant-v2` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@10-andruia-skill-smith` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@10-andruia-skill-smith-v2` - Use when the work is better handled by that native specialization after this imported skill establishes context.

## Additional Resources

Use this support matrix and the linked files below as the operator packet for this imported skill. They should reflect real copied source material, not generic scaffolding.

| Resource family | What it gives the reviewer | Example path |
| --- | --- | --- |
| `references` | copied reference notes, guides, or background material from upstream | `references/n/a` |
| `examples` | worked examples or reusable prompts copied from upstream | `examples/n/a` |
| `scripts` | upstream helper scripts that change execution or validation | `scripts/n/a` |
| `agents` | routing or delegation notes that are genuinely part of the imported package | `agents/n/a` |
| `assets` | supporting assets or schemas copied from the source package | `assets/n/a` |



### Imported Reference Notes

#### Imported: Additional Resources

- [Web.dev Performance](https://web.dev/performance/)
- [Core Web Vitals](https://web.dev/vitals/)
- [Lighthouse Documentation](https://developers.google.com/web/tools/lighthouse)
- [MDN Performance Guide](https://developer.mozilla.org/en-US/docs/Web/Performance)
- [Next.js Performance](https://nextjs.org/docs/advanced-features/measuring-performance)
- [Image Optimization Guide](https://web.dev/fast/#optimize-your-images)

---

**Pro Tip:** Focus on Core Web Vitals (LCP, FID, CLS) first - they have the biggest impact on user experience and SEO rankings!

#### Imported: Performance Audit Results

### Current Metrics (Before Optimization)
- **LCP (Largest Contentful Paint):** 4.2s ❌ (should be < 2.5s)
- **FID (First Input Delay):** 180ms ❌ (should be < 100ms)
- **CLS (Cumulative Layout Shift):** 0.25 ❌ (should be < 0.1)
- **Lighthouse Score:** 62/100

### Issues Identified

1. **LCP Issue:** Hero image (2.5MB) loads slowly
2. **FID Issue:** Large JavaScript bundle (850KB) blocks main thread
3. **CLS Issue:** Images without dimensions cause layout shifts

### Optimization Plan

#### Fix LCP (Largest Contentful Paint)

**Problem:** Hero image is 2.5MB and loads slowly

**Solutions:**
\`\`\`html
<!-- Before: Unoptimized image -->
<img src="/hero.jpg" alt="Hero">

<!-- After: Optimized with modern formats -->
<picture>
  <source srcset="/hero.avif" type="image/avif">
  <source srcset="/hero.webp" type="image/webp">
  <img
    src="/hero.jpg"
    alt="Hero"
    width="1200"
    height="600"
    loading="eager"
    fetchpriority="high"
  >
</picture>
\`\`\`

**Additional optimizations:**
- Compress image to < 200KB
- Use CDN for faster delivery
- Preload hero image: `<link rel="preload" as="image" href="/hero.avif">`

#### Fix FID (First Input Delay)

**Problem:** 850KB JavaScript bundle blocks main thread

**Solutions:**

1. **Code Splitting:**
\`\`\`javascript
// Before: Everything in one bundle
import { HeavyComponent } from './HeavyComponent';
import { Analytics } from './analytics';
import { ChatWidget } from './chat';

// After: Lazy load non-critical code
const HeavyComponent = lazy(() => import('./HeavyComponent'));
const ChatWidget = lazy(() => import('./chat'));

// Load analytics after page interactive
if (typeof window !== 'undefined') {
  window.addEventListener('load', () => {
    import('./analytics').then(({ Analytics }) => {
      Analytics.init();
    });
  });
}
\`\`\`

2. **Remove Unused Dependencies:**
\`\`\`bash
# Analyze bundle
npx webpack-bundle-analyzer

# Remove unused packages
npm uninstall moment  # Use date-fns instead (smaller)
npm install date-fns
\`\`\`

3. **Defer Non-Critical Scripts:**
\`\`\`html
<!-- Before: Blocks rendering -->
<script src="/analytics.js"></script>

<!-- After: Deferred -->
<script src="/analytics.js" defer></script>
\`\`\`

#### Fix CLS (Cumulative Layout Shift)

**Problem:** Images without dimensions cause layout shifts

**Solutions:**
\`\`\`html
<!-- Before: No dimensions -->
<img src="/product.jpg" alt="Product">

<!-- After: With dimensions -->
<img
  src="/product.jpg"
  alt="Product"
  width="400"
  height="300"
  style="aspect-ratio: 4/3;"
>
\`\`\`

**For dynamic content:**
\`\`\`css
/* Reserve space for content that loads later */
.skeleton-loader {
  min-height: 200px;
  background: linear-gradient(90deg, #f0f0f0 25%, #e0e0e0 50%, #f0f0f0 75%);
  background-size: 200% 100%;
  animation: loading 1.5s infinite;
}

@keyframes loading {
  0% { background-position: 200% 0; }
  100% { background-position: -200% 0; }
}
\`\`\`

### Results After Optimization

- **LCP:** 1.8s ✅ (improved by 57%)
- **FID:** 45ms ✅ (improved by 75%)
- **CLS:** 0.05 ✅ (improved by 80%)
- **Lighthouse Score:** 94/100 ✅
```

### Example 2: Reducing JavaScript Bundle Size

```markdown

#### Imported: Bundle Size Optimization

### Current State
- **Total Bundle:** 850KB (gzipped: 280KB)
- **Main Bundle:** 650KB
- **Vendor Bundle:** 200KB
- **Load Time (3G):** 8.2s

### Analysis

\`\`\`bash
# Analyze bundle composition
npx webpack-bundle-analyzer dist/stats.json
\`\`\`

**Findings:**
1. Moment.js: 67KB (can replace with date-fns: 12KB)
2. Lodash: 72KB (using entire library, only need 5 functions)
3. Unused code: ~150KB of dead code
4. No code splitting: Everything in one bundle

### Optimization Steps

#### 1. Replace Heavy Dependencies

\`\`\`bash
# Remove moment.js (67KB) → Use date-fns (12KB)
npm uninstall moment
npm install date-fns

# Before
import moment from 'moment';
const formatted = moment(date).format('YYYY-MM-DD');

# After
import { format } from 'date-fns';
const formatted = format(date, 'yyyy-MM-dd');
\`\`\`

**Savings:** 55KB

#### 2. Use Lodash Selectively

\`\`\`javascript
// Before: Import entire library (72KB)
import _ from 'lodash';
const unique = _.uniq(array);

// After: Import only what you need (5KB)
import uniq from 'lodash/uniq';
const unique = uniq(array);

// Or use native methods
const unique = [...new Set(array)];
\`\`\`

**Savings:** 67KB

#### 3. Implement Code Splitting

\`\`\`javascript
// Next.js example
import dynamic from 'next/dynamic';

// Lazy load heavy components
const Chart = dynamic(() => import('./Chart'), {
  loading: () => <div>Loading chart...</div>,
  ssr: false
});

const AdminPanel = dynamic(() => import('./AdminPanel'), {
  loading: () => <div>Loading...</div>
});

// Route-based code splitting (automatic in Next.js)
// pages/admin.js - Only loaded when visiting /admin
// pages/dashboard.js - Only loaded when visiting /dashboard
\`\`\`

#### 4. Remove Dead Code

\`\`\`javascript
// Enable tree shaking in webpack.config.js
module.exports = {
  mode: 'production',
  optimization: {
    usedExports: true,
    sideEffects: false
  }
};

// In package.json
{
  "sideEffects": false
}
\`\`\`

#### 5. Optimize Third-Party Scripts

\`\`\`html
<!-- Before: Loads immediately -->
<script src="https://analytics.com/script.js"></script>

<!-- After: Load after page interactive -->
<script>
  window.addEventListener('load', () => {
    const script = document.createElement('script');
    script.src = 'https://analytics.com/script.js';
    script.async = true;
    document.body.appendChild(script);
  });
</script>
\`\`\`

### Results

- **Total Bundle:** 380KB ✅ (reduced by 55%)
- **Main Bundle:** 180KB ✅
- **Vendor Bundle:** 80KB ✅
- **Load Time (3G):** 3.1s ✅ (improved by 62%)
```

### Example 3: Image Optimization Strategy

```markdown

#### Imported: Image Optimization

### Current Issues
- 15 images totaling 12MB
- No modern formats (WebP, AVIF)
- No responsive images
- No lazy loading

### Optimization Strategy

#### 1. Convert to Modern Formats

\`\`\`bash
# Install image optimization tools
npm install sharp

# Conversion script (optimize-images.js)
const sharp = require('sharp');
const fs = require('fs');
const path = require('path');

async function optimizeImage(inputPath, outputDir) {
  const filename = path.basename(inputPath, path.extname(inputPath));

  // Generate WebP
  await sharp(inputPath)
    .webp({ quality: 80 })
    .toFile(path.join(outputDir, \`\${filename}.webp\`));

  // Generate AVIF (best compression)
  await sharp(inputPath)
    .avif({ quality: 70 })
    .toFile(path.join(outputDir, \`\${filename}.avif\`));

  // Generate optimized JPEG fallback
  await sharp(inputPath)
    .jpeg({ quality: 80, progressive: true })
    .toFile(path.join(outputDir, \`\${filename}.jpg\`));
}

// Process all images
const images = fs.readdirSync('./images');
images.forEach(img => {
  optimizeImage(\`./images/\${img}\`, './images/optimized');
});
\`\`\`

#### 2. Implement Responsive Images

\`\`\`html
<!-- Responsive images with modern formats -->
<picture>
  <!-- AVIF for browsers that support it (best compression) -->
  <source
    srcset="
      /images/hero-400.avif 400w,
      /images/hero-800.avif 800w,
      /images/hero-1200.avif 1200w
    "
    type="image/avif"
    sizes="(max-width: 768px) 100vw, 50vw"
  >

  <!-- WebP for browsers that support it -->
  <source
    srcset="
      /images/hero-400.webp 400w,
      /images/hero-800.webp 800w,
      /images/hero-1200.webp 1200w
    "
    type="image/webp"
    sizes="(max-width: 768px) 100vw, 50vw"
  >

  <!-- JPEG fallback -->
  <img
    src="/images/hero-800.jpg"
    srcset="
      /images/hero-400.jpg 400w,
      /images/hero-800.jpg 800w,
      /images/hero-1200.jpg 1200w
    "
    sizes="(max-width: 768px) 100vw, 50vw"
    alt="Hero image"
    width="1200"
    height="600"
    loading="lazy"
  >
</picture>
\`\`\`

#### 3. Lazy Loading

\`\`\`html
<!-- Native lazy loading -->
<img
  src="/image.jpg"
  alt="Description"
  loading="lazy"
  width="800"
  height="600"
>

<!-- Eager loading for above-the-fold images -->
<img
  src="/hero.jpg"
  alt="Hero"
  loading="eager"
  fetchpriority="high"
>
\`\`\`

#### 4. Next.js Image Component

\`\`\`javascript
import Image from 'next/image';

// Automatic optimization
<Image
  src="/hero.jpg"
  alt="Hero"
  width={1200}
  height={600}
  priority  // For above-the-fold images
  quality={80}
/>

// Lazy loaded
<Image
  src="/product.jpg"
  alt="Product"
  width={400}
  height={300}
  loading="lazy"
/>
\`\`\`

### Results

| Metric | Before | After | Improvement |
|--------|--------|-------|-------------|
| Total Image Size | 12MB | 1.8MB | 85% reduction |
| LCP | 4.5s | 1.6s | 64% faster |
| Page Load (3G) | 18s | 4.2s | 77% faster |
```

#### Imported: Common Pitfalls

### Problem: Optimized for Desktop but Slow on Mobile
**Symptoms:** Good Lighthouse score on desktop, poor on mobile
**Solution:**
- Test on real mobile devices
- Use Chrome DevTools mobile throttling
- Optimize for 3G/4G networks
- Reduce JavaScript execution time
```bash
# Test with throttling
lighthouse https://yoursite.com --throttling.cpuSlowdownMultiplier=4
```

### Problem: Large JavaScript Bundle
**Symptoms:** Long Time to Interactive (TTI), high FID
**Solution:**
- Analyze bundle with webpack-bundle-analyzer
- Remove unused dependencies
- Implement code splitting
- Lazy load non-critical code
```bash
# Analyze bundle
npx webpack-bundle-analyzer dist/stats.json
```

### Problem: Images Causing Layout Shifts
**Symptoms:** High CLS score, content jumping
**Solution:**
- Always specify width and height
- Use aspect-ratio CSS property
- Reserve space with skeleton loaders
```css
img {
  aspect-ratio: 16 / 9;
  width: 100%;
  height: auto;
}
```

### Problem: Slow Server Response Time
**Symptoms:** High TTFB (Time to First Byte)
**Solution:**
- Implement server-side caching
- Use CDN for static assets
- Optimize database queries
- Consider static site generation (SSG)
```javascript
// Next.js: Static generation
export async function getStaticProps() {
  const data = await fetchData();
  return {
    props: { data },
    revalidate: 60 // Regenerate every 60 seconds
  };
}
```

#### Imported: Performance Checklist

### Images
- [ ] Convert to modern formats (WebP, AVIF)
- [ ] Implement responsive images
- [ ] Add lazy loading
- [ ] Specify dimensions (width/height)
- [ ] Compress images (< 200KB each)
- [ ] Use CDN for delivery

### JavaScript
- [ ] Bundle size < 200KB (gzipped)
- [ ] Implement code splitting
- [ ] Lazy load non-critical code
- [ ] Remove unused dependencies
- [ ] Minify and compress
- [ ] Use async/defer for scripts

### CSS
- [ ] Inline critical CSS
- [ ] Defer non-critical CSS
- [ ] Remove unused CSS
- [ ] Minify CSS files
- [ ] Use CSS containment

### Caching
- [ ] Set cache headers for static assets
- [ ] Implement service worker
- [ ] Use CDN caching
- [ ] Cache API responses
- [ ] Version static assets

### Core Web Vitals
- [ ] LCP < 2.5s
- [ ] FID < 100ms
- [ ] CLS < 0.1
- [ ] TTFB < 600ms
- [ ] TTI < 3.8s

#### Imported: Performance Tools

### Measurement Tools
- **Lighthouse** - Comprehensive performance audit
- **WebPageTest** - Detailed waterfall analysis
- **Chrome DevTools** - Performance profiling
- **PageSpeed Insights** - Real user metrics
- **Web Vitals Extension** - Monitor Core Web Vitals

### Analysis Tools
- **webpack-bundle-analyzer** - Visualize bundle composition
- **source-map-explorer** - Analyze bundle size
- **Bundlephobia** - Check package sizes before installing
- **ImageOptim** - Image compression tool

### Monitoring Tools
- **Google Analytics** - Track Core Web Vitals
- **Sentry** - Performance monitoring
- **New Relic** - Application performance monitoring
- **Datadog** - Real user monitoring

#### Imported: Limitations

- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.