---
title: Automatic Revalidation
type: conceptual
summary: Automatically revalidate stale data with focus, interval, and reconnect strategies.
prerequisites:
  - /docs/getting-started
related:
  - /docs/mutation
  - /docs/conditional-fetching
---

# Automatic Revalidation



<Callout>
  If you want to manually revalidate the data, check <Link href="/docs/mutation">mutation</Link>.
</Callout>

## Revalidate on Focus

When you re-focus a page or switch between tabs, SWR automatically revalidates data.

This can be useful to immediately synchronize to the latest state. This is helpful for refreshing data in scenarios like stale mobile tabs, or laptops that **went to sleep**.

<Bleed>
  <Video src="https://raw.githubusercontent.com/vercel/swr-site/master/.github/videos/focus-revalidate.mp4" caption="Video: using focus revalidation to automatically sync login state between pages." ratio={307/768} className="mx-8 2xl:mx-24" />
</Bleed>

This feature is enabled by default. You can disable it via the [`revalidateOnFocus`](/docs/api) option.

## Revalidate on Interval

In many cases, data changes because of multiple devices, multiple users, multiple tabs. How can we over time update the data on screen?

SWR will give you the option to automatically refetch data. It’s **smart** which means refetching will only happen if the component associated with the hook is **on screen**.

<Bleed>
  <Video src="https://raw.githubusercontent.com/vercel/swr-site/master/.github/videos/refetch-interval.mp4" caption="Video: when a user makes a change, both sessions will eventually render the same data." ratio={307/768} className="mx-8 2xl:mx-24" />
</Bleed>

You can enable it by setting a [`refreshInterval`](/docs/api) value:

```js
useSWR('/api/todos', fetcher, { refreshInterval: 1000 })
```

There're also options such as `refreshWhenHidden` and `refreshWhenOffline`. Both are disabled by default so SWR won't fetch when the webpage is not on screen, or there's no network connection.

## Revalidate on Reconnect

It's useful to also revalidate when the user is back online. This scenario happens a lot when the user unlocks their computer, but the internet is not yet connected at the same moment.

To make sure the data is always up-to-date, SWR automatically revalidates when network recovers.

This feature is enabled by default. You can disable it via the [`revalidateOnReconnect`](/docs/api) option.

## Disable Automatic Revalidations

If the resource is **immutable**, that will never change if we revalidate again, we can disable all kinds of automatic revalidations for it.

Since version 1.0, SWR provides a helper hook `useSWRImmutable` to mark the resource as immutable:

```js
import useSWRImmutable from 'swr/immutable'

// ...
useSWRImmutable(key, fetcher, options)
```

It has the same API interface as the normal `useSWR` hook. You can also do the same thing by disabling the following revalidation options:

```js
useSWR(key, fetcher, {
  revalidateIfStale: false,
  revalidateOnFocus: false,
  revalidateOnReconnect: false
})

// equivalent to
useSWRImmutable(key, fetcher)
```

The `revalidateIfStale` controls if SWR should revalidate when it mounts and there is stale data.

These 2 hooks above do the **exact same** thing. Once the data is cached, they will never request it again.

## Revalidate on Mount

It's useful to force override SWR revalidation on mounting. By default, the value of `revalidateOnMount` is set to undefined.

A SWR hook mounts as:

* First it checks if `revalidateOnMount` is defined. It starts request if it's true, stop if it's false.

`revalidateIfStale` useful to control the mount behaviour. By default `revalidateIfStale` is set to true.

If `revalidateIfStale` is set to true it only refetches if there's any cache data else it will not refetch.