Nitro is Nuxt's server engine. It handles API routes, server middleware, and deployment. You write your server code in server/, and Nitro compiles it for any hosting platform (Node, Cloudflare Workers, Vercel, Deno, etc.) with zero config changes.

API routes

Create files in server/api/ and they become endpoints automatically:

// server/api/hello.ts
export default defineEventHandler(() => {
  return { message: 'Hello from the server' }
})

This responds to all HTTP methods at /api/hello. To restrict to a specific method, add it to the filename:

// server/api/users.get.ts → GET /api/users
export default defineEventHandler(async () => {
  const users = await db.query('SELECT * FROM users')
  return users
})

// server/api/users.post.ts → POST /api/users
export default defineEventHandler(async (event) => {
  const body = await readBody(event)
  const user = await db.insert('users', body)
  return user
})

Server routes (non-API)

Files in server/routes/ work the same but without the /api prefix:

// server/routes/health.get.ts → GET /health
export default defineEventHandler(() => ({ status: 'ok' }))

Route and query parameters

// server/api/users/[id].ts → /api/users/42
export default defineEventHandler(async (event) => {
  const id = getRouterParam(event, 'id')
  return await db.findUser(id)
})

// server/api/search.get.ts → /api/search?q=vue&page=1
export default defineEventHandler((event) => {
  const { q, page } = getQuery(event)
  return searchArticles(q, Number(page) || 1)
})

Request body, headers, and cookies

export default defineEventHandler(async (event) => {
  const body = await readBody(event)

  const token = getHeader(event, 'authorization')

  const sessionId = getCookie(event, 'session')
  setCookie(event, 'visited', 'true', { httpOnly: true })

  return { received: body }
})

Error handling

Use createError to return proper HTTP errors:

export default defineEventHandler(async (event) => {
  const id = getRouterParam(event, 'id')
  const user = await db.findUser(id)

  if (!user) {
    throw createError({
      statusCode: 404,
      statusMessage: 'User not found'
    })
  }

  return user
})

Server utilities

Create reusable server-side logic in server/utils/. Files there are auto-imported across all server routes:

// server/utils/db.ts
export function getDb() {
  return useStorage('db')
}

// server/api/items.get.ts — no import needed
export default defineEventHandler(async () => {
  const db = getDb()
  return await db.getKeys()
})

Server plugins

Run code once when Nitro starts. Useful for database connections or scheduled jobs:

// server/plugins/db.ts
export default defineNitroPlugin((nitro) => {
  const pool = createPool(process.env.DATABASE_URL)

  nitro.hooks.hook('close', () => pool.end())
})

Nuxt 4 note: defineNitroPlugin is the Nuxt 3 API. In Nuxt 4, server plugins use definePlugin imported from 'nitro' instead. If you are migrating to Nuxt 4, replace defineNitroPlugin with import { definePlugin } from 'nitro'. Both APIs work the same way; only the import and function name change.

Calling server routes from the client

Use useFetch or $fetch. Both are type-safe when the server route is in your project:

<script setup>
// useFetch — SSR-aware, cached, reactive
const { data: users } = await useFetch('/api/users')

// $fetch — plain request, good for mutations
async function createUser(name: string) {
  const user = await $fetch('/api/users', {
    method: 'POST',
    body: { name }
  })
}
</script>

Directory structure

server/
├── api/              ← /api/* routes
│   ├── users.get.ts
│   ├── users.post.ts
│   └── users/
│       └── [id].ts
├── routes/           ← non-API routes (no /api prefix)
│   └── health.get.ts
├── middleware/        ← runs on every request
│   └── log.ts
├── plugins/          ← runs once at startup
│   └── db.ts
└── utils/            ← auto-imported server utilities
    └── db.ts

See also: What is the difference between server and route middleware? · How do you deploy a Nuxt app? · What is the Nuxt directory structure?

References

• Server Routes - Nuxt docs
• Nitro - Nitro docs
• Server API and Routes - Nuxt docs