Why Your Next.js Proxy (ex-Middleware) is Slow - By Sourav Mishra (@souravvmishra)

Next.js has officially moved from middleware.ts to proxy.ts. While the name has changed to better reflect its role as a network boundary, the specific performance pitfalls remain the same.

In this guide, I, Sourav Mishra, Co-founder of Codestam Technologies, analyze the most common performance killers I see in production proxy.ts files.

The Edge Runtime Constraint

Middleware runs on the Edge, which means:

1. No Node.js APIs: You can't use fs or native modules.
2. Lightweight: It needs to be fast.
3. Global: By default, it intercepts everything.

Anti-Pattern #1: Database Calls

❌ BAD: Connecting to a DB in proxy.ts.

// proxy.ts
import { db } from './lib/db'; // ⚠️ Don't do this

export async function proxy(req) { // Note the renamed export
  const user = await db.user.find(req.cookies.get('session'));
  if (!user) return Response.redirect('/login');
}

Why?: Establishing a TCP/SSL connection to a database adds 200ms+ to every single request. At Codestam, we saw a client's TTFB drop from 600ms to 120ms just by removing a single SQL query from their middleware.

✅ GOOD: Use Stateless Auth (JWT) or minimal Redis calls (via HTTP/REST, not TCP).

Anti-Pattern #2: Missing Matchers

❌ BAD: Running middleware on static assets.

// middleware.ts
// No config export

Why?: Your middleware is running on images, CSS files, and fonts.

✅ GOOD: Filter aggressively.

export const config = {
  matcher: ['/((?!api|_next/static|_next/image|favicon.ico).*)'],
};

Anti-Pattern #3: Blocking for Geolocation

Don't wait for external IP lookups. Use the geo object provided by Vercel/Next.js directly in the request.

// proxy.ts
export function proxy(req) {
  const country = req.geo?.country || 'US';
  // Immediate logic
}

Key Takeaways

• Rename to proxy.ts: If you haven't yet, run the codemod.
• Keep it logical: proxy is for routing and basic auth validation.
• Move data fetching: Do actual data checks in layout.tsx or Server Components.
• Use Matchers: Never let middleware run on static assets.

For optimizing your CSS delivery alongside this, check out Debugging Production CSS.

This guide was written by Sourav Mishra, Co-founder of Codestam Technologies and a Full Stack Engineer.