middleware.md

Middleware

Place a _.middleware.ts file in any routes/ subdirectory to intercept requests and responses for that subtree. Middleware applies from the root down — a _.middleware.ts at the root runs for every request.

// routes/_.middleware.ts
export async function middleware($, respondTo) {
  const response = await respondTo($);
  return response.header("X-Custom-Header", "Custom Value");
}

respondTo($) passes the request to the next middleware layer or the route handler, and returns the response. You can modify $ before calling respondTo, modify the response after, or both.

See also

• Patterns: Custom Middleware — authentication, headers, and logging across route groups
• Routes
• Reference
• Usage