You are currently viewing documentation for the canary channel of Next.js.

Analytics

Next.js has built-in support for measuring and reporting performance metrics. You can either use the useReportWebVitals hook to manage reporting yourself, or alternatively, Vercel provides a managed service to automatically collect and visualize metrics for you.

Build Your Own

app/_components/web-vitals.js

'use client'
 
import { useReportWebVitals } from 'next/web-vitals'
 
export function WebVitals() {
  useReportWebVitals((metric) => {
    console.log(metric)
  })
}

app/layout.js

import { WebVitals } from './_components/web-vitals'
 
export default function Layout({ children }) {
  return (
    <html>
      <body>
        <WebVitals />
        {children}
      </body>
    </html>
  )
}

Since the useReportWebVitals hook requires the "use client" directive, the most performant approach is to create a separate component that the root layout imports. This confines the client boundary exclusively to the WebVitals component.

View the API Reference for more information.

Web Vitals

Web Vitals are a set of useful metrics that aim to capture the user experience of a web page. The following web vitals are all included:

You can handle all the results of these metrics using the name property.

app/_components/web-vitals.tsx

'use client'
 
import { useReportWebVitals } from 'next/web-vitals'
 
export function WebVitals() {
  useReportWebVitals((metric) => {
    switch (metric.name) {
      case 'FCP': {
        // handle FCP results
      }
      case 'LCP': {
        // handle LCP results
      }
      // ...
    }
  })
}

Sending results to external systems

You can send results to any endpoint to measure and track real user performance on your site. For example:

useReportWebVitals((metric) => {
  const body = JSON.stringify(metric)
  const url = 'https://example.com/analytics'
 
  // Use `navigator.sendBeacon()` if available, falling back to `fetch()`.
  if (navigator.sendBeacon) {
    navigator.sendBeacon(url, body)
  } else {
    fetch(url, { body, method: 'POST', keepalive: true })
  }
})

Good to know: If you use Google Analytics, using the id value can allow you to construct metric distributions manually (to calculate percentiles, etc.)

useReportWebVitals((metric) => {
  // Use `window.gtag` if you initialized Google Analytics as this example:
  // https://github.com/vercel/next.js/blob/canary/examples/with-google-analytics
  window.gtag('event', metric.name, {
    value: Math.round(
      metric.name === 'CLS' ? metric.value * 1000 : metric.value
    ), // values must be integers
    event_label: metric.id, // id unique to current page load
    non_interaction: true, // avoids affecting bounce rate.
  })
})

Read more about sending results to Google Analytics.