Middleware

Middleware runs before a request is completed. It executes on the Edge Runtime and can rewrite, redirect, and protect routes.

Basics

• File at project root: middleware.js.
• Runs before routes, RSC rendering, and Route Handlers.
• Edge-only; no Node APIs.

import { NextResponse } from "next/server";
export function middleware(request) {
  return NextResponse.next();
}

Use cases

• Auth checks and redirects.

if (!isAuthenticated) return NextResponse.redirect(new URL("/login", request.url));

• Rewrites/redirects, i18n routing, feature flags, A/B tests.
• Page protection and bot blocking.

Matcher

export const config = { matcher: ["/dashboard/:path*"] };

Limitations

• No direct DB access, no Node APIs, no server-only libraries.