routing-middleware

Create a middleware.ts file at the project root with a default exported function that returns rewrite() or redirect responses. Use config.matcher to scope which paths trigger it, and import helpers like rewrite and geolocation from @vercel/functions for non-Next.js frameworks.

Next.js 16 renames middleware.ts to proxy.ts, which runs only on the Node.js runtime and clarifies its network-boundary role. The exported function must be renamed from middleware to proxy, and you can migrate with npx @next/codemod@latest middleware-to-proxy.

Yes, Vercel Routing Middleware is a platform feature that works with SvelteKit, Astro, Nuxt, or any deployed framework. For non-Next.js frameworks, import helpers like next, 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. Bun support is in Public Beta and reduces average latency by about 28% in CPU-bound workloads.

Avoid it when you need full Node.js APIs in Next.js (use proxy.ts), general edge compute (use Edge Functions), heavy business logic, or thousands of static redirects (use Bulk Redirects). It should also never be the sole auth layer.

Use project-level routes, which take effect instantly without a deployment. Manage them via the Dashboard CDN Routing tab, the REST API endpoints under /v1/projects/{projectId}/routes, the Vercel CLI, or the @vercel/config SDK helpers.