Caching and Revalidating Data in Next.js – Optimizing Performance with fetch, unstable_cache, and Smart Tags

Introduction

Caching stores the result of data fetching or computation to serve future requests faster. Revalidation updates cached data without rebuilding the entire application, ensuring freshness and performance.

Caching with fetch

By default, fetch requests are not cached. To enable caching, use cache: 'force-cache':

await fetch('https://...', { cache: 'force-cache' })

To revalidate data after a specific time, use next.revalidate:

await fetch('https://...', { next: { revalidate: 3600 } })

Caching async functions with unstable_cache

unstable_cache caches the result of async functions like database queries:

const getCachedUser = unstable_cache(
  async () => getUserById(userId),
  [userId],
  {
    tags: ['user'],
    revalidate: 3600,
  }
)

You can define tags and revalidation intervals for fine-grained control.

Revalidating with revalidateTag

revalidateTag refreshes cache entries by tag. Use 'max' for stale-while-revalidate behavior:

revalidateTag('user', 'max')

To tag fetch requests:

await fetch('https://...', { next: { tags: ['user'] } })

Or tag unstable_cache functions:

unstable_cache(..., ['user'], { tags: ['user'] })

Revalidating routes with revalidatePath

Use revalidatePath to refresh a specific route after a data mutation:

revalidatePath('/profile')

Immediate expiration with updateTag

updateTag is used in Server Actions to immediately expire cache entries. Ideal for read-your-own-writes scenarios:

updateTag('posts')
updateTag(`post-${post.id}`)

Key differences:

• updateTag: Server Actions only, immediate expiration
• revalidateTag: Server Actions and Route Handlers, supports stale-while-revalidate

Conclusion

With smart caching and targeted revalidation in Next.js, you can optimize performance, serve fresh data quickly, and avoid unnecessary route rebuilds. Tools like unstable_cache, revalidateTag, and updateTag give you precise control over cache behavior and data freshness.