performance-budget-setter

What this skill does

# Performance Budget Setter

Set and enforce performance budgets to maintain fast user experiences.

## Performance Budget Template

```markdown
# Performance Budget: E-Commerce Website

## Bundle Size Budget

| Asset Type             | Budget     | Current    | Status |
| ---------------------- | ---------- | ---------- | ------ |
| Initial JS             | 200 KB     | 185 KB     | ✅     |
| Initial CSS            | 50 KB      | 48 KB      | ✅     |
| Vendor JS              | 150 KB     | 145 KB     | ✅     |
| Fonts                  | 100 KB     | 95 KB      | ✅     |
| Images (above fold)    | 300 KB     | 320 KB     | ❌     |
| **Total Initial Load** | **800 KB** | **793 KB** | ✅     |

## API Latency Budget

| Endpoint       | p50    | p95    | p99     |
| -------------- | ------ | ------ | ------- |
| GET /products  | <100ms | <300ms | <500ms  |
| POST /checkout | <200ms | <500ms | <1000ms |
| GET /search    | <150ms | <400ms | <800ms  |

## Database Query Budget

| Query Type       | Budget | Current |
| ---------------- | ------ | ------- |
| Simple reads     | <50ms  | 42ms    |
| Complex joins    | <200ms | 185ms   |
| Aggregations     | <500ms | 450ms   |
| Queries per page | <20    | 18      |

## Core Web Vitals

| Metric                         | Good   | Poor   | Target |
| ------------------------------ | ------ | ------ | ------ |
| LCP (Largest Contentful Paint) | <2.5s  | >4.0s  | <2.0s  |
| FID (First Input Delay)        | <100ms | >300ms | <50ms  |
| CLS (Cumulative Layout Shift)  | <0.1   | >0.25  | <0.05  |

## Page-Specific Budgets

### Homepage

- Time to Interactive: <3s
- Total Blocking Time: <300ms
- Speed Index: <3s

### Product Page

- Time to Interactive: <4s
- Images loaded: <2s
- Reviews section: <1s

### Checkout

- Time to Interactive: <3s
- Payment processing: <2s
- Zero layout shifts

## Third-Party Scripts

| Service     | Budget     | Purpose          |
| ----------- | ---------- | ---------------- |
| Analytics   | 30 KB      | Google Analytics |
| Chat Widget | 50 KB      | Customer support |
| Payment     | 100 KB     | Stripe           |
| **Total**   | **180 KB** |                  |
```

## Enforcement Strategy

### 1. CI/CD Integration

```yaml
# .github/workflows/performance-budget.yml
name: Performance Budget Check

on: [pull_request]

jobs:
  budget-check:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2

      - name: Build production bundle
        run: npm run build

      - name: Check bundle size
        run: |
          npx bundlesize

      - name: Lighthouse CI
        run: |
          npm install -g @lhci/cli
          lhci autorun
```

### 2. Webpack Bundle Analyzer

```javascript
// webpack.config.js
const BundleAnalyzerPlugin =
  require("webpack-bundle-analyzer").BundleAnalyzerPlugin;

module.exports = {
  plugins: [
    new BundleAnalyzerPlugin({
      analyzerMode: process.env.ANALYZE ? "server" : "disabled",
    }),
  ],
  performance: {
    hints: "error",
    maxAssetSize: 200000, // 200 KB
    maxEntrypointSize: 400000, // 400 KB
  },
};
```

### 3. package.json Configuration

```json
{
  "bundlesize": [
    {
      "path": "./dist/js/main.*.js",
      "maxSize": "200 KB"
    },
    {
      "path": "./dist/css/main.*.css",
      "maxSize": "50 KB"
    },
    {
      "path": "./dist/js/vendor.*.js",
      "maxSize": "150 KB"
    }
  ]
}
```

## Monitoring Plan

### Real User Monitoring (RUM)

```typescript
// Track Core Web Vitals
import { getCLS, getFID, getFCP, getLCP, getTTFB } from "web-vitals";

function sendToAnalytics(metric) {
  const body = JSON.stringify(metric);

  if (navigator.sendBeacon) {
    navigator.sendBeacon("/analytics", body);
  } else {
    fetch("/analytics", { body, method: "POST", keepalive: true });
  }
}

getCLS(sendToAnalytics);
getFID(sendToAnalytics);
getLCP(sendToAnalytics);
```

### Synthetic Monitoring

```bash
# Lighthouse CI
lhci autorun --config=.lighthouserc.json

# WebPageTest API
curl "https://www.webpagetest.org/runtest.php?url=https://example.com&k=API_KEY"
```

### Performance Dashboard

```markdown
**Daily Metrics:**

- Bundle size trend
- API latency percentiles
- Core Web Vitals scores
- Page load times

**Alerts:**

- Bundle size exceeds budget by 10%
- LCP >2.5s for >5% of users
- API p95 >500ms
- Any metric exceeds budget
```

## Optimization Strategies

### Reduce Bundle Size

```typescript
// Code splitting
const ProductPage = lazy(() => import("./ProductPage"));

// Tree shaking
import { specific } from "library"; // ✅
import * as library from "library"; // ❌

// Dynamic imports
if (featureFlag) {
  const module = await import("./feature");
}
```

### Optimize API Calls

```typescript
// Parallel requests
const [user, orders] = await Promise.all([fetchUser(id), fetchOrders(id)]);

// Caching
const cachedData = await redis.get(key);
if (cachedData) return cachedData;

// Pagination
const products = await db.products
  .find()
  .limit(20)
  .skip((page - 1) * 20);
```

### Optimize Database Queries

```sql
-- Add indexes
CREATE INDEX idx_orders_user_created ON orders(user_id, created_at);

-- Limit columns
SELECT id, name FROM products; -- ✅
SELECT * FROM products;        -- ❌

-- Use EXPLAIN
EXPLAIN ANALYZE SELECT ...;
```

## Budget Violation Response

### When Budget Exceeded

1. **Immediate:**

   - Block PR from merging
   - Notify team in Slack
   - Create ticket

2. **Within 24 hours:**

   - Investigate cause
   - Identify optimization opportunities
   - Propose fix or budget increase

3. **Decision:**
   - Fix code (preferred)
   - Increase budget (requires justification)

### Budget Increase Request Template

```markdown
## Budget Increase Request

**Component:** Main JS bundle
**Current Budget:** 200 KB
**Requested Budget:** 250 KB
**Reason:** Added critical feature X

**Impact Analysis:**

- Load time increase: +0.5s
- User impact: Medium
- Revenue impact: Unknown

**Alternatives Considered:**

1. Code splitting: Reduces to 210 KB (preferred)
2. Remove feature Y: Reduces to 195 KB (rejected)
3. Lazy loading: Complex, 3 weeks effort

**Recommendation:** Implement code splitting
```

## Best Practices

1. **Set realistic budgets**: Based on user data
2. **Enforce in CI**: Automated checks
3. **Monitor continuously**: RUM + synthetic
4. **Review quarterly**: Adjust as needed
5. **Prioritize UX**: User-centric metrics
6. **Document exceptions**: Why budget increased
7. **Celebrate wins**: When under budget

## Output Checklist

- [ ] Bundle size budgets defined
- [ ] API latency targets set
- [ ] Database query budgets
- [ ] Core Web Vitals targets
- [ ] Page-specific budgets
- [ ] CI/CD enforcement configured
- [ ] Monitoring dashboard
- [ ] Alert thresholds set
- [ ] Violation response process
- [ ] Regular review schedule