Middleware

Middleware is a special file (middleware.ts) that sits between the user and your application.

Every time a user makes a request to a route, the Middleware function executes first. It can inspect the request (like checking cookies or geolocation), and decide whether to let the request through, redirect it, rewrite it, or block it entirely.

Imagine you have a /dashboard with 20 sub-pages. You could write an authentication check inside every single page component.

However, this is repetitive, and worse, the user's request still has to hit your main server just to be rejected.

Middleware runs at the 'Edge' (servers geographically closest to the user). It can instantly reject unauthenticated users and redirect them to /login before your main server is even contacted, saving resources and speeding up response times.

typescript

// middleware.ts (Root level, not in /app)

import { NextResponse } from 'next/server';

import type { NextRequest } from 'next/server';

export function middleware(request: NextRequest) {

const session = request.cookies.get('session');

if (!session) {

return NextResponse.redirect(new URL('/login', request.url));

}

return NextResponse.next();

}

// Only run on specific paths

export const config = {

matcher: ['/dashboard/:path*'],

};