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# Next.js adapter

The `@mastra/next` package mounts Mastra in a Next.js App Router application. See [Server Adapters](https://mastra.ai/docs/server/server-adapters) for general adapter concepts.

## Installation

Install the Next.js adapter and its Hono peer dependency:

**npm**:

```bash
npm install @mastra/next@latest hono
```

**pnpm**:

```bash
pnpm add @mastra/next@latest hono
```

**Yarn**:

```bash
yarn add @mastra/next@latest hono
```

**Bun**:

```bash
bun add @mastra/next@latest hono
```

## Usage example

Mount the adapter in a catch-all App Router route:

```typescript
import { createNextRouteHandler } from '@mastra/next'
import { mastra } from '@/mastra'

export const { GET, POST, PUT, DELETE, PATCH, OPTIONS, HEAD } = createNextRouteHandler({
  mastra,
})
```

The `prefix` option defaults to `/api` and must match the catch-all route's mount path. For example, when mounting at `app/api/mastra/[...mastra]/route.ts`, use `createNextRouteHandler({ mastra, prefix: '/api/mastra' })`.

## Signature

```typescript
function createNextRouteHandler(options: NextRouteHandlerOptions): NextRouteHandlers
```

## Parameters

**mastra** (`Mastra`): Mastra instance whose server configuration and registered resources are exposed

**tools** (`ToolsInput`): Additional tools to register with the server (Default: `{}`)

**prefix** (`string`): API route prefix, which must match the catch-all route mount path (Default: `'/api'`)

## Return value

Returns a `NextRouteHandlers` object with `GET`, `POST`, `PUT`, `DELETE`, `PATCH`, `OPTIONS`, and `HEAD` properties. Each property is a handler with this signature:

```typescript
(request: Request) => Response | Promise<Response>
```

## Serverless deployments & lazy initialization

The adapter exports its route handlers synchronously, then creates the underlying Hono app and `MastraServer` when the first request arrives. That initialized app is reused for subsequent requests in the same process, which supports serverless runtimes without top-level asynchronous initialization.

A2A endpoints use an in-memory task store. Task state lasts only for the lifetime of the process and isn't shared between serverless instances.

## Body size limit

Request bodies have a default limit of 4.5 MB. Requests that exceed the limit receive `{ error: 'Request body too large' }`.

Set `server.bodySizeLimit` on the `Mastra` instance to configure the limit.

## Middleware

Middleware configured with `server.middleware` or `setServerMiddleware()` runs through the adapter's Hono-based server, except on framework-public routes such as those marked `requiresAuth: false`. See [Server middleware](https://mastra.ai/docs/server/middleware).

## Related

- [Server Adapters](https://mastra.ai/docs/server/server-adapters)
- [MastraServer](https://mastra.ai/reference/server/mastra-server)