app-router

Included with Lifetime

$97 forever

This skill should be used when the user asks to "create a Next.js route", "add a page", "set up layouts", "implement loading states", "add error boundaries", "organize routes", "create dynamic routes", or needs guidance on Next.js App Router file conventions and routing patterns.

Web Dev

What this skill does


# Next.js App Router Patterns

## Overview

The App Router is Next.js's file-system based router built on React Server Components. It uses a `app/` directory structure where folders define routes and special files control UI behavior.

## Core File Conventions

### Route Files

Each route segment is defined by a folder. Special files within folders control behavior:

| File | Purpose |
|------|---------|
| `page.tsx` | Unique UI for a route, makes route publicly accessible |
| `layout.tsx` | Shared UI wrapper, preserves state across navigations |
| `loading.tsx` | Loading UI using React Suspense |
| `error.tsx` | Error boundary for route segment |
| `not-found.tsx` | UI for 404 responses |
| `template.tsx` | Like layout but re-renders on navigation |
| `default.tsx` | Fallback for parallel routes |

### Folder Conventions

| Pattern | Purpose | Example |
|---------|---------|---------|
| `folder/` | Route segment | `app/blog/` → `/blog` |
| `[folder]/` | Dynamic segment | `app/blog/[slug]/` → `/blog/:slug` |
| `[...folder]/` | Catch-all segment | `app/docs/[...slug]/` → `/docs/*` |
| `[[...folder]]/` | Optional catch-all | `app/shop/[[...slug]]/` → `/shop` or `/shop/*` |
| `(folder)/` | Route group (no URL) | `app/(marketing)/about/` → `/about` |
| `@folder/` | Named slot (parallel routes) | `app/@modal/login/` |
| `_folder/` | Private folder (excluded) | `app/_components/` |

## Creating Routes

### Basic Route Structure

To create a new route, add a folder with `page.tsx`:

```
app/
├── page.tsx              # / (home)
├── about/
│   └── page.tsx          # /about
└── blog/
    ├── page.tsx          # /blog
    └── [slug]/
        └── page.tsx      # /blog/:slug
```

### Page Component

A page is a Server Component by default:

```tsx
// app/about/page.tsx
export default function AboutPage() {
  return (
    <main>
      <h1>About Us</h1>
      <p>Welcome to our company.</p>
    </main>
  )
}
```

### Dynamic Routes

Access route parameters via the `params` prop:

```tsx
// app/blog/[slug]/page.tsx
interface PageProps {
  params: Promise<{ slug: string }>
}

export default async function BlogPost({ params }: PageProps) {
  const { slug } = await params
  const post = await getPost(slug)

  return <article>{post.content}</article>
}
```

## Layouts

### Root Layout (Required)

Every app needs a root layout with `<html>` and `<body>`:

```tsx
// app/layout.tsx
export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <html lang="en">
      <body>{children}</body>
    </html>
  )
}
```

### Nested Layouts

Layouts wrap their children and preserve state:

```tsx
// app/dashboard/layout.tsx
export default function DashboardLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <div className="flex">
      <Sidebar />
      <main className="flex-1">{children}</main>
    </div>
  )
}
```

## Loading and Error States

### Loading UI

Create instant loading states with Suspense:

```tsx
// app/dashboard/loading.tsx
export default function Loading() {
  return <div className="animate-pulse">Loading...</div>
}
```

### Error Boundaries

Handle errors gracefully:

```tsx
// app/dashboard/error.tsx
'use client'

export default function Error({
  error,
  reset,
}: {
  error: Error
  reset: () => void
}) {
  return (
    <div>
      <h2>Something went wrong!</h2>
      <button onClick={reset}>Try again</button>
    </div>
  )
}
```

## Route Groups

Organize routes without affecting URL structure:

```
app/
├── (marketing)/
│   ├── layout.tsx        # Marketing layout
│   ├── about/page.tsx    # /about
│   └── contact/page.tsx  # /contact
└── (shop)/
    ├── layout.tsx        # Shop layout
    └── products/page.tsx # /products
```

## Metadata

### Static Metadata

```tsx
// app/about/page.tsx
import { Metadata } from 'next'

export const metadata: Metadata = {
  title: 'About Us',
  description: 'Learn more about our company',
}
```

### Dynamic Metadata

```tsx
// app/blog/[slug]/page.tsx
export async function generateMetadata({ params }: PageProps): Promise<Metadata> {
  const { slug } = await params
  const post = await getPost(slug)
  return { title: post.title }
}
```

## Key Patterns

1. **Colocation**: Keep components, tests, and styles near routes
2. **Private folders**: Use `_folder` for non-route files
3. **Route groups**: Use `(folder)` to organize without URL impact
4. **Parallel routes**: Use `@slot` for complex layouts
5. **Intercepting routes**: Use `(.)` patterns for modals

## Resources

For detailed patterns, see:
- `references/routing-conventions.md` - Complete file conventions
- `references/layouts-templates.md` - Layout composition patterns
- `references/loading-error-states.md` - Suspense and error handling
- `examples/dynamic-routes.md` - Dynamic routing examples
- `examples/parallel-routes.md` - Parallel and intercepting routes

Files: 6

Size: 37.1 KB

Complexity: 54/100

Category: Web Dev

Source: https://github.com/davepoon/buildwithclaude/tree/main/plugins/nextjs-expert/skills/app-router

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