Middleware

Middleware is a single function that runs on every matching request, before any page or route handler. It runs on the Edge runtime by default — fast, but with a restricted Node API.

The file

Create middleware.js at the root of the project (next to app/, not inside it).

// middleware.js
import { NextResponse } from "next/server";

export function middleware(request) {
  const { pathname } = request.nextUrl;

  if (pathname.startsWith("/admin")) {
    const isLoggedIn = Boolean(request.cookies.get("session"));
    if (!isLoggedIn) {
      return NextResponse.redirect(new URL("/login", request.url));
    }
  }

  return NextResponse.next();
}

export const config = {
  matcher: ["/admin/:path*", "/account/:path*"],
};

What middleware can return

• **NextResponse.next()** — continue to the page.
• **NextResponse.redirect(url)** — send the user elsewhere.
• **NextResponse.rewrite(url)** — keep the URL but render a different route.
• **new Response(body, init)** — short-circuit with your own response (e.g., 401).

Matchers

The matcher config narrows down which paths trigger middleware. Use it religiously — running middleware on every static asset is wasteful.

export const config = {
  matcher: [
    "/dashboard/:path*",
    "/api/:path*",
    {
      source: "/((?!_next/static|_next/image|favicon.ico).*)",
      missing: [{ type: "header", key: "x-skip-mw" }],
    },
  ],
};

Setting headers and cookies on responses

const res = NextResponse.next();
res.cookies.set("session-touched", Date.now().toString());
res.headers.set("x-country", request.geo?.country ?? "unknown");
return res;