Next.js Middleware: Auth Guards, Rate Limiting, and Edge Functions Explained

Next.js Middleware runs on every request before it hits your routes. It's the right place for auth guards, rate limiting, geo-redirects, and A/B testing -- all at the Edge. Here's how to use it correctly without tanking performance. What Middleware Is Middleware runs in the Edge Runtime -- a lightweight V8 environment that starts instantly worldwide. It intercepts requests before they reach your Next.js routes. // middleware.ts (at the project root, not inside /app) import { NextRequest , NextResponse } from ' next/server ' export function middleware ( request : NextRequest ) { // Runs before every matched request return NextResponse . next () } export const config = { matcher : [ ' /((?!_next/static|_next/image|favicon.ico).*) ' ], } The matcher config controls which routes trigger middleware. Be specific -- running on static assets wastes cycles. Auth Guard Pattern Protect routes without touching every page component: import { NextRequest , NextResponse } from ' next/server ' import