cache-components

Next.js Cache Components

> Auto-activation: This skill activates automatically in projects with cacheComponents: true in next.config.

Project Detection

When starting work in a Next.js project, check if Cache Components are enabled:

# Check next.config.ts or next.config.js for cacheComponents
grep -r "cacheComponents" next.config.* 2>/dev/null

If cacheComponents: true is found, apply this skill's patterns proactively when:

• Writing React Server Components
• Implementing data fetching
• Creating Server Actions with mutations
• Optimizing page performance
• Reviewing existing component code

Cache Components enable Partial Prerendering (PPR) - mixing static HTML shells with dynamic streaming content for optimal performance.

Philosophy: Code Over Configuration

Cache Components represents a shift from segment configuration to compositional code:

Key Principle: Components co-locate their caching, not just their data. Next.js provides build-time feedback to guide you toward optimal patterns.

Core Concept

┌─────────────────────────────────────────────────────┐
│                   Static Shell                       │
│  (Sent immediately to browser)                       │
│                                                      │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐  │
│  │   Header    │  │  Cached     │  │  Suspense   │  │
│  │  (static)   │  │  Content    │  │  Fallback   │  │
│  └─────────────┘  └─────────────┘  └──────┬──────┘  │
│                                           │         │
│                                    ┌──────▼──────┐  │
│                                    │  Dynamic    │  │
│                                    │  (streams)  │  │
│                                    └─────────────┘  │
└─────────────────────────────────────────────────────┘

Mental Model: The Caching Decision Tree

When writing a React Server Component, ask these questions in order:

┌─────────────────────────────────────────────────────────┐
│ Does this component fetch data or perform I/O?          │
└─────────────────────┬───────────────────────────────────┘
                      │
           ┌──────────▼──────────┐
           │   YES               │ NO → Pure component, no action needed
           └──────────┬──────────┘
                      │
    ┌─────────────────▼─────────────────┐
    │ Does it depend on request context? │
    │ (cookies, headers, searchParams)   │
    └─────────────────┬─────────────────┘
                      │
         ┌────────────┴────────────┐
         │                         │
    ┌────▼────┐              ┌─────▼─────┐
    │   YES   │              │    NO     │
    └────┬────┘              └─────┬─────┘
         │                         │
         │                   ┌─────▼─────────────────┐
         │                   │ Can this be cached?   │
         │                   │ (same for all users?) │
         │                   └─────┬─────────────────┘
         │                         │
         │              ┌──────────┴──────────┐
         │              │                     │
         │         ┌────▼────┐          ┌─────▼─────┐
         │         │   YES   │          │    NO     │
         │         └────┬────┘          └─────┬─────┘
         │              │                     │
         │              ▼                     │
         │         'use cache'                │
         │         + cacheTag()               │
         │         + cacheLife()              │
         │                                    │
         └──────────────┬─────────────────────┘
                        │
                        ▼
              Wrap in <Suspense>
              (dynamic streaming)

Key insight: The 'use cache' directive is for data that's the _same across users_. User-specific data stays dynamic with Suspense.

Quick Start

Enable Cache Components

// next.config.ts
import type { NextConfig } from 'next'

const nextConfig: NextConfig = {
  cacheComponents: true,
}

export default nextConfig

Basic Usage

// Cached component - output included in static shell
async function CachedPosts() {
  'use cache'
  const posts = await db.posts.findMany()
  return <PostList posts={posts} />
}

// Page with static + cached + dynamic content
export default async function BlogPage() {
  return (
    <>
      <Header /> {/* Static */}
      <CachedPosts /> {/* Cached */}
      <Suspense fallback={<Skeleton />}>
        <DynamicComments /> {/* Dynamic - streams */}
      </Suspense>
    </>
  )
}

Core APIs

1. 'use cache' Directive

Marks code as cacheable. Can be applied at three levels:

// File-level: All exports are cached
'use cache'
export async function getData() {
  /* ... */
}
export async function Component() {
  /* ... */
}

// Component-level
async function UserCard({ id }: { id: string }) {
  'use cache'
  const user = await fetchUser(id)
  return <Card>{user.name}</Card>
}

// Function-level
async function fetchWithCache(url: string) {
  'use cache'
  return fetch(url).then((r) => r.json())
}

Important: All cached functions must be async.

2. cacheLife() - Control Cache Duration

import { cacheLife } from 'next/cache'

async function Posts() {
  'use cache'
  cacheLife('hours') // Use a predefined profile

  // Or custom configuration:
  cacheLife({
    stale: 60, // 1 min - client cache validity
    revalidate: 3600, // 1 hr - start background refresh
    expire: 86400, // 1 day - absolute expiration
  })

  return await db.posts.findMany()
}

Predefined profiles: 'default', 'seconds', 'minutes', 'hours', 'days', 'weeks', 'max'

3. cacheTag() - Tag for Invalidation

import { cacheTag } from 'next/cache'

async function BlogPosts() {
  'use cache'
  cacheTag('posts')
  cacheLife('days')

  return await db.posts.findMany()
}

async function UserProfile({ userId }: { userId: string }) {
  'use cache'
  cacheTag('users', `user-${userId}`) // Multiple tags

  return await db.users.findUnique({ where: { id: userId } })
}

4. updateTag() - Immediate Invalidation

For read-your-own-writes semantics:

'use server'
import { updateTag } from 'next/cache'

export async function createPost(formData: FormData) {
  await db.posts.create({ data: formData })

  updateTag('posts') // Client immediately sees fresh data
}

5. revalidateTag() - Background Revalidation

For stale-while-revalidate pattern:

'use server'
import { revalidateTag } from 'next/cache'

export async function updatePost(id: string, data: FormData) {
  await db.posts.update({ where: { id }, data })

  revalidateTag('posts', 'max') // Serve stale, refresh in background
}

When to Use Each Pattern

Parameter Permutations & Subshells

Critical Concept: With Cache Components, Next.js renders ALL permutations of provided parameters to create reusable subshells.

// app/products/[category]/[slug]/page.tsx
export async function generateStaticParams() {
  return [
    { category: 'jackets', slug: 'classic-bomber' },
    { category: 'jackets', slug: 'essential-windbreaker' },
    { category: 'accessories', slug: 'thermal-fleece-gloves' },
  ]
}

Next.js renders these routes:

/products/jackets/classic-bomber        ← Full params (complete page)
/products/jackets/essential-windbreaker ← Full params (complete page)
/products/accessories/thermal-fleece-gloves ← Full params (complete page)
/products/jackets/[slug]                ← Partial params (category subshell)
/products/accessories/[slug]            ← Partial params (category subshell)
/products/[category]/[slug]             ← No params (fallback shell)

Why this matters: The category subshell (/products/jackets/[slug]) can be reused for ANY jacket product, even ones not in generateStaticParams. Users navigating to an unlisted jacket get the cached category shell immediately, with product details streaming in.

generateStaticParams Requirements

With Cache Components enabled:

1. Must provide at least one parameter - Empty arrays now cause build errors (prevents silent production failures)
2. Params prove static safety - Providing params lets Next.js verify no dynamic APIs are called
3. Partial params create subshells - Each unique permutation generates a reusable shell

// ❌ ERROR with Cache Components
export function generateStaticParams() {
  return [] // Build error: must provide at least one param
}

// ✅ CORRECT: Provide real params
export async function generateStaticParams() {
  const products = await getPopularProducts()
  return products.map(({ category, slug }) => ({ category, slug }))
}

Cache Key = Arguments

Arguments become part of the cache key:

// Different userId = different cache entry
async function UserData({ userId }: { userId: string }) {
  'use cache'
  cacheTag(`user-${userId}`)

  return await fetchUser(userId)
}

Build-Time Feedback

Cache Components provides early feedback during development. These build errors guide you toward optimal patterns:

Error: Dynamic data outside Suspense

Error: Accessing cookies/headers/searchParams outside a Suspense boundary

Solution: Wrap dynamic components in <Suspense>:

<Suspense fallback={<Skeleton />}>
  <ComponentThatUsesCookies />
</Suspense>

Error: Uncached data outside Suspense

Error: Accessing uncached data outside Suspense

Solution: Either cache the data or wrap in Suspense:

// Option 1: Cache it
async function ProductData({ id }: { id: string }) {
  'use cache'
  return await db.products.findUnique({ where: { id } })
}

// Option 2: Make it dynamic with Suspense
;<Suspense fallback={<Loading />}>
  <DynamicProductData id={id} />
</Suspense>

Error: Request data inside cache

Error: Cannot access cookies/headers inside 'use cache'

Solution: Extract runtime data outside cache boundary (see "Handling Runtime Data" above).

Additional Resources

• For complete API reference, see [REFERENCE.md](REFERENCE.md)
• For common patterns and recipes, see [PATTERNS.md](PATTERNS.md)
• For debugging and troubleshooting, see [TROUBLESHOOTING.md](TROUBLESHOOTING.md)

Code Generation Guidelines

When generating Cache Component code:

1. Always use `async` - All cached functions must be async
2. Place `'use cache'` first - Must be first statement in function body
3. Call `cacheLife()` early - Should follow 'use cache' directive
4. Tag meaningfully - Use semantic tags that match your invalidation needs
5. Extract runtime data - Move cookies()/headers() outside cached scope
6. Wrap dynamic content - Use <Suspense> for non-cached async components

Proactive Application (When Cache Components Enabled)

When cacheComponents: true is detected in the project, automatically apply these patterns:

When Writing Data Fetching Components

Ask yourself: "Can this data be cached?" If yes, add 'use cache':

// Before: Uncached fetch
async function ProductList() {
  const products = await db.products.findMany()
  return <Grid products={products} />
}

// After: With caching
async function ProductList() {
  'use cache'
  cacheTag('products')
  cacheLife('hours')

  const products = await db.products.findMany()
  return <Grid products={products} />
}

When Writing Server Actions

Always invalidate relevant caches after mutations:

'use server'
import { updateTag } from 'next/cache'

export async function createProduct(data: FormData) {
  await db.products.create({ data })
  updateTag('products') // Don't forget!
}

When Composing Pages

Structure with static shell + cached content + dynamic streaming:

export default async function Page() {
  return (
    <>
      <StaticHeader /> {/* No cache needed */}
      <CachedContent /> {/* 'use cache' */}
      <Suspense fallback={<Skeleton />}>
        <DynamicUserContent /> {/* Streams at runtime */}
      </Suspense>
    </>
  )
}

When Reviewing Code

Flag these issues in Cache Components projects:

• [ ] Data fetching without 'use cache' where caching would benefit
• [ ] Missing cacheTag() calls (makes invalidation impossible)
• [ ] Missing cacheLife() (relies on defaults which may not be appropriate)
• [ ] Server Actions without updateTag()/revalidateTag() after mutations
• [ ] cookies()/headers() called inside 'use cache' scope
• [ ] Dynamic components without <Suspense> boundaries
• [ ] DEPRECATED: export const revalidate - replace with cacheLife() in 'use cache'
• [ ] DEPRECATED: export const dynamic - replace with Suspense + cache boundaries
• [ ] Empty generateStaticParams() return - must provide at least one param