Next.js App Router Patterns

Comprehensive patterns for Next.js 14+ App Router architecture, Server Components, and modern full-stack React development.

When to Use This Skill

Building new Next.js applications with App Router
Migrating from Pages Router to App Router
Implementing Server Components and streaming
Setting up parallel and intercepting routes
Optimizing data fetching and caching
Building full-stack features with Server Actions

Core Concepts

1. Rendering Modes

Mode	Where	When to Use
Server Components	Server only	Data fetching, heavy computation, secrets
Client Components	Browser	Interactivity, hooks, browser APIs
Static	Build time	Content that rarely changes
Dynamic	Request time	Personalized or real-time data
Streaming	Progressive	Large pages, slow data sources

2. File Conventions

app/
├── layout.tsx       # Shared UI wrapper
├── page.tsx         # Route UI
├── loading.tsx      # Loading UI (Suspense)
├── error.tsx        # Error boundary
├── not-found.tsx    # 404 UI
├── route.ts         # API endpoint
├── template.tsx     # Re-mounted layout
├── default.tsx      # Parallel route fallback
└── opengraph-image.tsx  # OG image generation

Quick Start

// app/layout.tsx
import { Inter } from 'next/font/google'
import { Providers } from './providers'

const inter = Inter({ subsets: ['latin'] })

export const metadata = {
  title: { default: 'My App', template: '%s | My App' },
  description: 'Built with Next.js App Router',
}

export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <html lang="en" suppressHydrationWarning>
      <body className={inter.className}>
        <Providers>{children}</Providers>
      </body>
    </html>
  )
}

// app/page.tsx - Server Component by default
async function getProducts() {
  const res = await fetch('https://api.example.com/products', {
    next: { revalidate: 3600 }, // ISR: revalidate every hour
  })
  return res.json()
}

export default async function HomePage() {
  const products = await getProducts()

  return (
    <main>
      <h1>Products</h1>
      <ProductGrid products={products} />
    </main>
  )
}

Detailed patterns and worked examples

Detailed pattern documentation lives in references/details.md. Read that file when the navigation tier above is insufficient.

Best Practices

Do's

Start with Server Components - Add 'use client' only when needed
Colocate data fetching - Fetch data where it's used
Use Suspense boundaries - Enable streaming for slow data
Leverage parallel routes - Independent loading states
Use Server Actions - For mutations with progressive enhancement

Don'ts

Don't pass serializable data - Server → Client boundary limitations
Don't use hooks in Server Components - No useState, useEffect
Don't fetch in Client Components - Use Server Components or React Query
Don't over-nest layouts - Each layout adds to the component tree
Don't ignore loading states - Always provide loading.tsx or Suspense