Next.js App Router (Next.js 16+)

Build modern React applications using Next.js 16+ with App Router architecture.

Overview

This skill provides patterns for Server Components (default) and Client Components ("use client"), Server Actions for mutations and form handling, Route Handlers for API endpoints, explicit caching with "use cache" directive, parallel and intercepting routes, and Next.js 16 async APIs and proxy.ts.

When to Use

Activate when user requests involve:

• "Create a Next.js 16 project", "Set up App Router"
• "Server Component", "Client Component", "use client"
• "Server Action", "form submission", "mutation"
• "Route Handler", "API endpoint", "route.ts"
• "use cache", "cacheLife", "cacheTag", "revalidation"
• "parallel routes", "@slot", "intercepting routes"
• "proxy.ts", "migrate from middleware.ts"
• "layout.tsx", "page.tsx", "loading.tsx", "error.tsx", "not-found.tsx"
• "generateMetadata", "next/image", "next/font"

Quick Reference

Instructions

Create New Project

npx create-next-app@latest my-app --typescript --tailwind --app --turbopack

Server Component

Server Components are the default in App Router. They run on the server and can use async/await.

// app/users/page.tsx
async function getUsers() {
  const apiUrl = process.env.API_URL;
  const res = await fetch(`${apiUrl}/users`);
  return res.json();
}

export default async function UsersPage() {
  const users = await getUsers();
  return <main>{users.map(user => <UserCard key={user.id} user={user} />)}</main>;
}

Client Component

Add "use client" when using hooks, browser APIs, or event handlers.

"use client";

import { useState } from "react";

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

Server Action

Define actions in separate files with "use server" directive.

// app/actions.ts
"use server";

import { revalidatePath } from "next/cache";

export async function createUser(formData: FormData) {
  const name = formData.get("name") as string;
  const email = formData.get("email") as string;
  await db.user.create({ data: { name, email } });
  revalidatePath("/users");
}

Use with forms in Client Components:

"use client";

import { useActionState } from "react";
import { createUser } from "./actions";

export default function UserForm() {
  const [state, formAction, pending] = useActionState(createUser, {});
  return (
    <form action={formAction}>
      <input name="name" />
      <input name="email" type="email" />
      <button type="submit" disabled={pending}>{pending ? "Creating..." : "Create"}</button>
    </form>
  );
}

See references/server-actions.md for Zod validation, optimistic updates, and advanced patterns.

Configure Caching

Use "use cache" directive for explicit caching (Next.js 16+).

"use cache";

import { cacheLife, cacheTag } from "next/cache";

export default async function ProductPage({ params }: { params: Promise<{ id: string }> }) {
  const { id } = await params;
  cacheTag(`product-${id}`);
  cacheLife("hours");
  const product = await fetchProduct(id);
  return <ProductDetail product={product} />;
}

See references/caching-strategies.md for cache profiles, on-demand revalidation, and advanced patterns.

Route Handler

// app/api/users/route.ts
import { NextRequest, NextResponse } from "next/server";

export async function GET(request: NextRequest) {
  return NextResponse.json(await db.user.findMany());
}

export async function POST(request: NextRequest)