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{/* The content of this doc is shared between the app and pages router. You can use the <PagesOnly>Content</PagesOnly> component to add content that is specific to the Pages Router. Any shared content should not be wrapped in a component. */}
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.
For more advanced analytics and monitoring needs, Next.js provides a instrumentation-client.js|ts file that runs before your application's frontend code starts executing. This is ideal for setting up global analytics, error tracking, or performance monitoring tools.
To use it, create an instrumentation-client.js or instrumentation-client.ts file in your application's root directory:
// Initialize analytics before the app starts
console.log('Analytics initialized')
// Set up global error tracking
window.addEventListener('error', (event) => {
// Send to your error tracking service
reportError(event.error)
})
import { useReportWebVitals } from 'next/web-vitals'
function MyApp({ Component, pageProps }) {
useReportWebVitals((metric) => {
console.log(metric)
})
return <Component {...pageProps} />
}
View the API Reference for more information.
</PagesOnly> <AppOnly>'use client'
import { useReportWebVitals } from 'next/web-vitals'
export function WebVitals() {
useReportWebVitals((metric) => {
console.log(metric)
})
}
import { WebVitals } from './_components/web-vitals'
export default function Layout({ children }) {
return (
<html>
<body>
<WebVitals />
{children}
</body>
</html>
)
}
Since the
useReportWebVitalshook 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 theWebVitalscomponent.
View the API Reference for more information.
</AppOnly>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.
import { useReportWebVitals } from 'next/web-vitals'
function MyApp({ Component, pageProps }) {
useReportWebVitals((metric) => {
switch (metric.name) {
case 'FCP': {
// handle FCP results
}
case 'LCP': {
// handle LCP results
}
// ...
}
})
return <Component {...pageProps} />
}
'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
}
// ...
}
})
}
'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
}
// ...
}
})
}
In addition to the core metrics listed above, there are some additional custom metrics that measure the time it takes for the page to hydrate and render:
Next.js-hydration: Length of time it takes for the page to start and finish hydrating (in ms)Next.js-route-change-to-render: Length of time it takes for a page to start rendering after a
route change (in ms)Next.js-render: Length of time it takes for a page to finish render after a route change (in ms)You can handle all the results of these metrics separately:
export function reportWebVitals(metric) {
switch (metric.name) {
case 'Next.js-hydration':
// handle hydration results
break
case 'Next.js-route-change-to-render':
// handle route-change to render results
break
case 'Next.js-render':
// handle render results
break
default:
break
}
}
These metrics work in all browsers that support the User Timing API.
</PagesOnly>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
idvalue 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.
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