Next.js App Router API route returns 405 Method Not Allowed

Problem

API route in Next.js 13+ App Router returns 405 Method Not Allowed even though the handler is defined correctly.

Symptoms

• 405 Method Not Allowed
• POST request returns 405
• API route works with GET but not POST

Stack

Solution

In App Router, API routes use route.ts (not pages/api). You must export named functions matching HTTP methods (GET, POST, PUT, DELETE) — not a default export.

Code

// app/api/users/route.ts

// BAD (Pages Router style):
export default function handler(req, res) { ... }

// GOOD (App Router):
export async function GET(request: Request) {
  const data = await getUsers();
  return Response.json(data);
}

export async function POST(request: Request) {
  const body = await request.json();
  const user = await createUser(body);
  return Response.json(user, { status: 201 });
}

Caveats

File must be named route.ts, not page.ts. You cannot have both page.tsx and route.ts in the same directory.