In Next.js 15, API routes are created using the App Router with a file named route.ts or route.js inside the app/api directory. Here's a minimal example:

bash
app/api/hello/route.ts

ts
export async function GET() {
  return new Response(JSON.stringify({ message: 'Hello world' }), {
    status: 200,
    headers: { 'Content-Type': 'application/json' }
  })
}

You can now access the API at /api/hello.

Would you like an example with POST or dynamic routes?

ts
import { create } from 'zustand'

const useStore = create((set, get) => ({
  data: null,
  fetchData: async () => {
    const res = await fetch('/api/hello')
    if (!res.ok) return
    const json = await res.json()
    set({ data: json })
  }
}))

ts
import { create } from 'zustand'

const useStore = create((set, get) => ({
  note: null,
  fetchNote: async (name) => {
    const res = await fetch(`/api/notes/${encodeURIComponent(name)}`)
    if (!res.ok) return
    const json = await res.json()
    set({ note: json })
  }
}))

ts
// app/api/notes/[name]/route.ts

import { NextRequest } from 'next/server'

export async function GET(
  req: NextRequest,
  { params }: { params: { name: string } }
) {
  const { name } = params

  // example response
  return new Response(
    JSON.stringify({ note: `Content for ${name}` }),
    {
      status: 200,
      headers: { 'Content-Type': 'application/json' }
    }
  )
}

Yes, you can define a generic type for the context parameter. Here's how to do it cleanly with a Params type:

ts
import { NextRequest } from 'next/server'

type Params = {
  name: string
}

export async function GET(
  req: NextRequest,
  context: { params: Params }
) {
  const { name } = context.params

  return new Response(
    JSON.stringify({ note: `Content for ${name}` }),
    {
      status: 200,
      headers: { 'Content-Type': 'application/json' }
    }
  )
}

This keeps your types reusable and clear. Do you want to handle query parameters or just route params like this?

To use a query string (e.g. /api/notes?name=test) instead of a dynamic route, do this:

ts
// app/api/notes/route.ts

import { NextRequest } from 'next/server'

export async function GET(req: NextRequest) {
  const { searchParams } = new URL(req.url)
  const name = searchParams.get('name')

  if (!name) {
    return new Response(
      JSON.stringify({ error: 'Missing name param' }),
      { status: 400 }
    )
  }

  return new Response(
    JSON.stringify({ note: `Content for ${name}` }),
    {
      status: 200,
      headers: { 'Content-Type': 'application/json' }
    }
  )
}

Then fetch it with:

ts
await fetch('/api/notes?name=test')

Do you prefer this over route parameters?

ts
const getNoteUrl = (name) => {
  const params = new URLSearchParams({ name })
  return `/api/notes?${params.toString()}`
}

// usage
const url = getNoteUrl('example')
const res = await fetch(url)