/cache-components

name: cache-components
description: |
  Expert guidance for Next.js Cache Components and Partial Prerendering (PPR).

  **PROACTIVE ACTIVATION**: Use this skill automatically when working in Next.js projects that have `cacheComponents: true` in their next.config.ts/next.config.js. When this config is detected, proactively apply Cache Components patterns and best practices to all React Server Component implementations.

  **DETECTION**: At the start of a session in a Next.js project, check for `cacheComponents: true` in next.config. If enabled, this skill's patterns should guide all component authoring, data fetching, and caching decisions.

  **USE CASES**: Implementing 'use cache' directive, configuring cache lifetimes with cacheLife(), tagging cached data with cacheTag(), invalidating caches with updateTag()/revalidateTag(), optimizing static vs dynamic content boundaries, debugging cache issues, and reviewing Cache Component implementations.

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**:

| Before (Deprecated) | After (Cache Components) | | --------------------------------------- | ----------------------------------------- | | `export const revalidate = 3600` | `cacheLife('hours')` inside `'use cache'` | | `export const dynamic = 'force-static'` | Use `'use cache'` and Suspense boundaries | | All-or-nothing static/dynamic | Granular: static shell + cached + dynamic |

**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 */}