rsnext/errors/middleware-parse-user-agent.mdx

---
title: Removed parsed User Agent from Middleware API
---

## Why This Error Occurred

Your application is interacting with `req.ua` which has been deprecated.

```ts filename="middleware.ts"
import { NextRequest, NextResponse } from 'next/server'

export function middleware(request: NextRequest) {
  const viewport = request.ua.device.type === 'mobile' ? 'mobile' : 'desktop'

  request.nextUrl.searchParams.set('viewport', viewport)
  return NextResponse.rewrites(request.nextUrl)
}
```

## Possible Ways to Fix It

The internal logic has been moved into a separate `userAgent` function that you can import from `next/server` and wrap your request instead.

```ts filename="middleware.ts"
import { NextRequest, NextResponse, userAgent } from 'next/server'

export function middleware(request: NextRequest) {
  const { device } = userAgent(request)
  const viewport = device.type === 'mobile' ? 'mobile' : 'desktop'

  request.nextUrl.searchParams.set('viewport', viewport)
  return NextResponse.rewrite(request.nextUrl)
}
```