What are Route Handlers (API routes) in the App Router?

Question

Accepted Answer

**Route Handlers** are the App Router's way to build API endpoints — backend HTTP handlers that live in your Next.js project. You create them with a **`route.ts`** file, exporting functions named after HTTP methods.

## Defining an endpoint

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

export async function GET() {
  const users = await db.user.findMany();
  return NextResponse.json(users);             // GET /api/users
}

export async function POST(req: NextRequest) {
  const body = await req.json();               // read the request body
  const user = await db.user.create({ data: body });
  return NextResponse.json(user, { status: 201 }); // POST /api/users
}
```

Each exported method (`GET`, `POST`, `PUT`, `PATCH`, `DELETE`) handles that verb. They use the standard Web `Request`/`Response` APIs (via `NextRequest`/`NextResponse`).

## Reading params and query

```ts
// app/api/users/[id]/route.ts → /api/users/123
export async function GET(req: NextRequest, { params }: { params: { id: string } }) {
  const url = new URL(req.url);
  const sort = url.searchParams.get("sort"); // ?sort=name
  const user = await db.user.findUnique({ where: { id: params.id } });
  return NextResponse.json(user);
}
```

## When to use Route Handlers vs Server Actions/Components

```text
Use Route Handlers for:
  ✓ Public APIs consumed by mobile apps / external clients
  ✓ Webhooks (Stripe, GitHub) — they need a URL endpoint
  ✓ Returning non-HTML (JSON, files, images, RSS)
  ✓ Client-side fetch() targets

Prefer Server Components for reading data into your own pages,
and Server Actions for form mutations — they avoid a manual API layer.
```

## Other capabilities

```ts
export const runtime = "edge";       // run on the Edge runtime
export const dynamic = "force-dynamic"; // opt out of caching
// Handlers can also stream responses, set cookies, and handle CORS.
```

## Why it matters

Route Handlers make Next.js full-stack: you build REST/JSON APIs, webhooks, and file endpoints alongside your frontend with web-standard `Request`/`Response`.

Knowing when to reach for them (external clients, webhooks, non-HTML responses) versus using Server Components/Actions (internal data reads and mutations) is key to structuring an App Router backend cleanly.