Next.js App Router

Expert knowledge for building modern web applications with Next.js App Router.

Next.js 16.1.1 highlights

• Turbopack improvements: faster next dev restarts (project-dependent)
• Bundle Analyzer (experimental): next experimental-analyze
• Easier Debugging: next dev --inspect
• Upgrade Command: next upgrade
• MCP Server: Built-in /_next/mcp endpoint for coding agents

MCP Server (Coding Agents)

Next.js 16+ includes MCP support for AI coding agents via next-devtools-mcp:

Setup

// .mcp.json at project root
{
  "mcpServers": {
    "next-devtools": {
      "command": "npx",
      "args": ["-y", "next-devtools-mcp@latest"]
    }
  }
}

Available Tools

Capabilities

• Error Detection: Real-time build/runtime/type errors
• Live State Queries: Access application state and runtime info
• Page Metadata: Query routes, components, rendering details
• Server Actions: Inspect Server Actions and component hierarchies
• Knowledge Base: Query Next.js documentation
• Migration Tools: Automated upgrade helpers with codemods
• Playwright Integration: Browser testing via Playwright MCP

Core Concepts

Server Components (Default)

All components in the app/ directory are Server Components by default:

// app/posts/page.tsx - Server Component
export default async function PostsPage() {
  const posts = await db.post.findMany();

  return (
    <ul>
      {posts.map((post) => (
        <li key={post.id}>{post.title}</li>
      ))}
    </ul>
  );
}

Client Components

Use 'use client' directive for interactivity:

'use client';

import { useState } from 'react';

export function Counter() {
  const [count, setCount] = useState(0);
  return <button onClick={() => setCount((c) => c + 1)}>{count}</button>;
}

Server Actions

Use 'use server' for mutations:

'use server';

import { revalidatePath } from 'next/cache';

export async function createPost(formData: FormData) {
  await db.post.create({ data: { title: formData.get('title') } });
  revalidatePath('/posts');
}

File Conventions

References

• references/routing.md – Routing patterns
• references/data-fetching.md – Data fetching strategies
• references/server-actions.md – Server Actions guide

Assets

• assets/page.tsx – Basic page template
• assets/layout.tsx – Layout template
• assets/route-handler.ts – API route template
• assets/server-action.ts – Server Action template
• assets/middleware.ts – Middleware template