routing-middleware

Create a middleware.ts file at the project root with a default exported function that returns rewrite(url) from @vercel/functions. Use config.matcher to scope which paths trigger the middleware and avoid unnecessary invocations.

Next.js 16 renames middleware.ts to proxy.ts, running only on the Node.js runtime at the network boundary. The exported function must also be renamed from middleware to proxy, and a codemod (npx @next/codemod middleware-to-proxy) automates migration.

Yes, Vercel Routing Middleware is a platform feature that works with SvelteKit, Astro, Nuxt, or any deployed framework. Non-Next.js projects import helpers like rewrite, geolocation, and ipAddress from @vercel/functions.

Yes, add bunVersion to vercel.json and set the middleware runtime to nodejs; Bun transparently replaces the Node.js runtime. The feature is in Public Beta and supports Next.js, Express, Hono, and Nitro.

Avoid it for heavy business logic, database queries, or as the sole auth layer. Use Bulk Redirects for thousands of static redirects, Edge Functions for general edge compute, and server-side framework features for full Node.js API needs.