Performance monitoring tracks how fast your application loads for real users. It captures Core Web Vitals — the metrics Google uses for search rankings.

Performance testing in development doesn’t reflect real-world conditions. Users on slow networks with older devices may have a very different experience. Real User Monitoring (RUM) captures actual user data.

export function reportWebVitals(metric: any) {
  console.log(metric) // name, value, rating, delta, id

  // Send to analytics
  const body = {
    name: metric.name,
    value: metric.value,
    rating: metric.rating,
    delta: metric.delta,
    id: metric.id,
    page: window.location.pathname,
  }

  fetch('/api/analytics', {
    method: 'POST',
    body: JSON.stringify(body),
  })
}

If deployed on Vercel, enable “Web Vitals” in the Analytics dashboard. This automatically captures real user metrics without any code changes.

Run Lighthouse in Chrome DevTools or via CLI:

npx lighthouse https://yourdomain.com --view

Lighthouse gives you scores and specific improvement suggestions for each metric.

Set targets for key metrics and alert when they’re exceeded:

const PERFORMANCE_BUDGETS = {
  lcp: 2500,    // 2.5s
  fid: 100,     // 100ms
  cls: 0.1,     // 0.1 score
  tti: 3000,    // 3s
  bundleSize: 200 * 1024, // 200KB
}

• Only testing on fast connections — Test on Slow 3G throttling and mid-range devices.
• Ignoring CLS — Layout shifts are often missed in development. Test with real content.
• Not monitoring after deployment — Performance can regress with any change. Monitor continuously.

• Monitor real user metrics (RUM), not just Lighthouse scores
• Test on actual mobile devices and throttled networks
• Track performance changes over time to catch regressions
• Set up alerts when Core Web Vitals exceed targets

Performance monitoring captures real user experience with Core Web Vitals. Use reportWebVitals, Vercel Analytics, and Lighthouse to measure and improve. Monitor continuously — performance is not a one-time fix.

• Analytics
• Logging
• Error Monitoring