Next.js middleware

Serve markdown twins from Next.js middleware or proxy.ts.

Next.js middleware runs before routing, so it can answer .md URLs and negotiated requests without any route handlers. On Next.js 16 the file is proxy.ts and the export is named proxy. On Next.js 15 and earlier it is middleware.ts with an export named middleware.

import { NextResponse, type NextRequest } from "next/server";

import { twins } from "@/lib/agentside";

export function proxy(request: NextRequest) {
  return twins.handle(request, async () => NextResponse.next());
}

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

NextRequest extends the fetch Request, so it can be passed straight to handle. For HTML pages Agentside adds Link and Vary to the NextResponse.next() response and Next.js merges those headers into the rendered page.

import { agentside } from "@usenotra/agentside";

import { getPost } from "@/lib/posts";

export const twins = agentside({
  routes: {
    "/": "# Acme\n\nAcme sends invoices your customers actually pay.",
    "/blog/[slug]": async ({ params }) => (await getPost(params.slug))?.markdown ?? null,
  },
});

Serving from a route handler

If you would rather keep middleware out of it, rewrite .md URLs to a route handler and call serve there.

import { twins } from "@/lib/agentside";

export async function GET(request: Request, { params }: { params: Promise<{ path: string[] }> }) {
  const { path } = await params;
  return twins.serve(request, `/${path.join("/")}`);
}

This only covers explicit .md URLs. Negotiation by Accept and user agent still needs the middleware.