start-core/server-routes

Server routes are API endpoints defined alongside app routes in the src/routes directory. They use the server property on createFileRoute and handle raw HTTP requests.

Basic Server Route

// src/routes/api/hello.ts
import { createFileRoute } from "@tanstack/react-router"

export const Route = createFileRoute("/api/hello")({
  server: {
    handlers: {
      GET: async ({ request }) => {
        return new Response("Hello, World!")
      },
    },
  },
})

Combining Server Route and App Route

The same file can define both a server route and a UI route:

// src/routes/hello.tsx
import { createFileRoute } from "@tanstack/react-router"
import { useState } from "react"

export const Route = createFileRoute("/hello")({
  server: {
    handlers: {
      POST: async ({ request }) => {
        const body = await request.json()
        return Response.json({ message: `Hello, ${body.name}!` })
      },
    },
  },
  component: HelloComponent,
})

function HelloComponent() {
  const [reply, setReply] = useState("")
  return (
    <button
      onClick={() => {
        fetch("/hello", {
          method: "POST",
          headers: { "Content-Type": "application/json" },
          body: JSON.stringify({ name: "Tanner" }),
        })
          .then((res) => res.json())
          .then((data) => setReply(data.message))
      }}
    >
      Say Hello {reply && `- ${reply}`}
    </button>
  )
}

File Route Conventions

Server routes follow TanStack Router file-based routing conventions:

File	Route
routes/users.ts	/users
routes/users/$id.ts	/users/$id
routes/users/$id/posts.ts	/users/$id/posts
routes/api/file/$.ts	/api/file/$ (splat)
routes/my-script[.]js.ts	/my-script.js (escaped dot)

Unique Route Paths

Each route can only have a single handler file. These would conflict:

• routes/users.ts
• routes/users.index.ts
• routes/users/index.ts

Handler Context

Each handler receives:

• request — the incoming Request object
• params — dynamic path parameters
• context — context from middleware
• pathname — the matched pathname
• next — call to fall through to SSR (returns a Response)

Dynamic Path Params

// routes/users/$id.ts
import { createFileRoute } from "@tanstack/react-router"

export const Route = createFileRoute("/users/$id")({
  server: {
    handlers: {
      GET: async ({ params }) => {
        return new Response(`User ID: ${params.id}`)
      },
    },
  },
})

Splat/Wildcard Params

// routes/file/$.ts
import { createFileRoute } from "@tanstack/react-router"

export const Route = createFileRoute("/file/$")({
  server: {
    handlers: {
      GET: async ({ params }) => {
        return new Response(`File: ${params._splat}`)
      },
    },
  },
})

Request Body Handling

export const Route = createFileRoute("/api/users")({
  server: {
    handlers: {
      POST: async ({ request }) => {
        const body = await request.json()
        return Response.json({ created: body.name })
      },
    },
  },
})

Other body methods: request.text(), request.formData().

JSON Responses

// Using Response.json helper
handlers: {
  GET: async () => {
    return Response.json({ message: 'Hello!' })
  },
}

Status Codes and Headers

handlers: {
  GET: async ({ params }) => {
    const user = await findUser(params.id)
    if (!user) {
      return new Response('Not found', { status: 404 })
    }
    return Response.json(user)
  },
}

handlers: {
  GET: async () => {
    return new Response('Hello', {
      headers: { 'Content-Type': 'text/plain' },
    })
  },
}

Middleware on Server Routes

All handlers

export const Route = createFileRoute("/api/admin")({
  server: {
    middleware: [authMiddleware, loggerMiddleware],
    handlers: {
      GET: async ({ context }) => Response.json(context.user),
      POST: async ({ request, context }) => {
        /* ... */
      },
    },
  },
})

Specific handlers with createHandlers

export const Route = createFileRoute("/api/data")({
  server: {
    handlers: ({ createHandlers }) =>
      createHandlers({
        GET: async () => Response.json({ public: true }),
        POST: {
          middleware: [authMiddleware],
          handler: async ({ context }) => {
            return Response.json({ user: context.session.user })
          },
        },
      }),
  },
})

Combined route-level and handler-specific

export const Route = createFileRoute("/api/posts")({
  server: {
    middleware: [authMiddleware], // runs first for all
    handlers: ({ createHandlers }) =>
      createHandlers({
        GET: async () => Response.json([]),
        POST: {
          middleware: [validationMiddleware], // runs after auth, POST only
          handler: async ({ request }) => {
            const body = await request.json()
            return Response.json({ created: true })
          },
        },
      }),
  },
})

Common Mistakes

1. MEDIUM: Duplicate route paths

# WRONG — both resolve to /users, causes error
routes/users.ts
routes/users/index.ts

# CORRECT — pick one
routes/users.ts

2. MEDIUM: Forgetting to await request body methods

// WRONG — body is a Promise, not the actual data
const body = request.json()

// CORRECT — await the promise
const body = await request.json()

Cross-References

• start-core/middleware — middleware for server routes
• start-core/server-functions — alternative for RPC-style calls