What Is Middleware

middleware.ts at the project root runs before a request is matched to a page or route handler. It can redirect, rewrite, set headers or cookies, or return a response directly.

// middleware.ts
import { NextRequest, NextResponse } from 'next/server';

export function middleware(request: NextRequest) {
  console.log(request.method, request.nextUrl.pathname);
  return NextResponse.next(); // continue to the page
}

Next.js 16 renames the file to proxy.ts and the function to proxy, to make clear that it sits in front of the app like a network proxy. It runs on the Node.js runtime by default. middleware.ts still works in 16 but is deprecated.

// proxy.ts (Next.js 16)
import { NextRequest, NextResponse } from 'next/server';

export function proxy(request: NextRequest) {
  return NextResponse.next();
}

npx @next/codemod@canary middleware-to-proxy .

  ✓ Renamed middleware.ts -> proxy.ts