Next.js Middleware Reference Cheat Sheet

Last Updated: November 21, 2025

Middleware Focus

Purpose	Approach
`Routing`	Use middleware.ts with NextResponse.rewrite or redirect.
`Headers`	Copy or strip headers via NextResponse.next() and response.headers.
`Edge runtime`	No Node APIs—use Web Crypto and fetch instead.
`Matchers`	Limit files with export const config = { matcher: ['/dashboard/:path*'] }.


         import { NextResponse } from 'next/server'

Construct responses that run on the edge.


         export function middleware(request)

Run before every matched request to inspect cookies or rewrite.


         return NextResponse.rewrite(new URL('/app', request.url))

Move traffic without a client redirect.


         request.nextUrl.searchParams.set('utm_source', 'middleware')

Augment URLs before continuing.

Middleware lets you guard routes, mutate headers, and rewrite traffic at the edge—keep it fast by avoiding heavy computations.

💡 Pro Tip: Test middleware via next dev and check both edge and node runtimes to catch mismatched globals.