---
title: useReportWebVitals
description: API Reference for the useReportWebVitals function.
---

{/* 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. */}

The `useReportWebVitals` hook allows you to report [Core Web Vitals](https://web.dev/vitals/), and can be used in combination with your analytics service.

<PagesOnly>

```jsx filename="pages/_app.js"
import { useReportWebVitals } from 'next/web-vitals'

function MyApp({ Component, pageProps }) {
  useReportWebVitals((metric) => {
    console.log(metric)
  })

  return <Component {...pageProps} />
}
```

</PagesOnly>

<AppOnly>

```jsx filename="app/_components/web-vitals.js"
'use client'

import { useReportWebVitals } from 'next/web-vitals'

export function WebVitals() {
  useReportWebVitals((metric) => {
    console.log(metric)
  })
}
```

```jsx filename="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.

</AppOnly>

## useReportWebVitals

The `metric` object passed as the hook's argument consists of a number of properties:

- `id`: Unique identifier for the metric in the context of the current page load
- `name`: The name of the performance metric. Possible values include names of [Web Vitals](#web-vitals) metrics (TTFB, FCP, LCP, FID, CLS) specific to a web application.
- `delta`: The difference between the current value and the previous value of the metric. The value is typically in milliseconds and represents the change in the metric's value over time.
- `entries`: An array of [Performance Entries](https://developer.mozilla.org/en-US/docs/Web/API/PerformanceEntry) associated with the metric. These entries provide detailed information about the performance events related to the metric.
- `navigationType`: Indicates the [type of navigation](https://developer.mozilla.org/en-US/docs/Web/API/PerformanceNavigationTiming/type) that triggered the metric collection. Possible values include `"navigate"`, `"reload"`, `"back_forward"`, and `"prerender"`.
- `rating`: A qualitative rating of the metric value, providing an assessment of the performance. Possible values are `"good"`, `"needs-improvement"`, and `"poor"`. The rating is typically determined by comparing the metric value against predefined thresholds that indicate acceptable or suboptimal performance.
- `value`: The actual value or duration of the performance entry, typically in milliseconds. The value provides a quantitative measure of the performance aspect being tracked by the metric. The source of the value depends on the specific metric being measured and can come from various [Performance API](https://developer.mozilla.org/en-US/docs/Web/API/Performance_API)s.

## Web Vitals

[Web Vitals](https://web.dev/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:

- [Time to First Byte](https://developer.mozilla.org/en-US/docs/Glossary/Time_to_first_byte) (TTFB)
- [First Contentful Paint](https://developer.mozilla.org/en-US/docs/Glossary/First_contentful_paint) (FCP)
- [Largest Contentful Paint](https://web.dev/lcp/) (LCP)
- [First Input Delay](https://web.dev/fid/) (FID)
- [Cumulative Layout Shift](https://web.dev/cls/) (CLS)
- [Interaction to Next Paint](https://web.dev/inp/) (INP)

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

<PagesOnly>

```jsx filename="pages/_app.js"
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} />
}
```

</PagesOnly>

<AppOnly>

```tsx filename="app/components/web-vitals.tsx" switcher
'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
      }
      // ...
    }
  })
}
```

```jsx filename="app/components/web-vitals.js" switcher
'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
      }
      // ...
    }
  })
}
```

</AppOnly>

<PagesOnly>

## Custom Metrics

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:

```js
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](https://caniuse.com/#feat=user-timing).

</PagesOnly>

## Usage on Vercel

[Vercel Speed Insights](https://vercel.com/docs/concepts/speed-insights) are automatically configured on Vercel deployments, and don't require the use of `useReportWebVitals`. This hook is useful in local development, or if you're using a different analytics service.

## Sending results to external systems

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

```js
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](https://analytics.google.com/analytics/web/), using the
> `id` value can allow you to construct metric distributions manually (to calculate percentiles,
> etc.)

> ```js
> 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/pages/_app.js
>   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](https://github.com/GoogleChrome/web-vitals#send-the-results-to-google-analytics).
