start-core/server-routes

Create a file in src/routes and use createFileRoute with the server property containing handlers for HTTP methods like GET or POST. Each handler receives the request object and returns a standard Response, such as Response.json for JSON payloads.

Add a middleware array to the server property to run middleware for all handlers, or use createHandlers to attach middleware to specific handlers like POST only. Route-level middleware runs first, followed by handler-specific middleware.

Yes, a single route file can define both server handlers and a UI component on the same createFileRoute call. The component renders for browser navigation while the handlers respond to direct HTTP method requests like POST.

Handlers receive a params object containing dynamic path segments, such as params.id for a $id.ts file. Splat routes defined with $.ts expose the wildcard portion through params._splat.

Request body methods like request.json(), request.text(), and request.formData() return Promises that must be awaited. Forgetting await leaves you with an unresolved Promise instead of the parsed body content.

Use server routes when you need raw HTTP control over methods, headers, and status codes for REST-style APIs or webhooks. Use server functions for RPC-style calls from your React components where HTTP semantics are unnecessary.