next.js/docs/01-app/03-api-reference/03-file-conventions/middleware.mdx

---
title: middleware.js
description: API reference for the middleware.js file.
related:
  title: Learn more about Middleware
  links:
    - app/api-reference/functions/next-request
    - app/api-reference/functions/next-response
---

The `middleware.js|ts` file is used to write [Middleware](/docs/app/api-reference/file-conventions/middleware) and run code on the server before a request is completed. Then, based on the incoming request, you can modify the response by rewriting, redirecting, modifying the request or response headers, or responding directly.

Middleware executes before routes are rendered. It's particularly useful for implementing custom server-side logic like authentication, logging, or handling redirects.

Use the file `middleware.ts` (or .js) in the root of your project to define Middleware. For example, at the same level as `app` or `pages`, or inside `src` if applicable.

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

// This function can be marked `async` if using `await` inside
export function middleware(request: NextRequest) {
  return NextResponse.redirect(new URL('/home', request.url))
}

export const config = {
  matcher: '/about/:path*',
}
```

```js filename="middleware.js" switcher
import { NextResponse } from 'next/server'

// This function can be marked `async` if using `await` inside
export function middleware(request) {
  return NextResponse.redirect(new URL('/home', request.url))
}

export const config = {
  matcher: '/about/:path*',
}
```

## Exports

### Middleware function

The file must export a single function, either as a default export or named `middleware`. Note that multiple middleware from the same file are not supported.

```js filename="middleware.js"
// Example of default export
export default function middleware(request) {
  // Middleware logic
}
```

### Config object (optional)

Optionally, a config object can be exported alongside the Middleware function. This object includes the [matcher](#matcher) to specify paths where the Middleware applies.

### Matcher

The `matcher` option allows you to target specific paths for the Middleware to run on. You can specify these paths in several ways:

- For a single path: Directly use a string to define the path, like `'/about'`.
- For multiple paths: Use an array to list multiple paths, such as `matcher: ['/about', '/contact']`, which applies the Middleware to both `/about` and `/contact`.

```js filename="middleware.js"
export const config = {
  matcher: ['/about/:path*', '/dashboard/:path*'],
}
```

Additionally, the `matcher` option supports complex path specifications through regular expressions, such as `matcher: ['/((?!api|_next/static|_next/image|.*\\.png$).*)']`, enabling precise control over which paths to include or exclude.

The `matcher` option accepts an array of objects with the following keys:

- `source`: The path or pattern used to match the request paths. It can be a string for direct path matching or a pattern for more complex matching.
- `regexp` (optional): A regular expression string that fine-tunes the matching based on the source. It provides additional control over which paths are included or excluded.
- `locale` (optional): A boolean that, when set to `false`, ignores locale-based routing in path matching.
- `has` (optional): Specifies conditions based on the presence of specific request elements such as headers, query parameters, or cookies.
- `missing` (optional): Focuses on conditions where certain request elements are absent, like missing headers or cookies.

```js filename="middleware.js"
export const config = {
  matcher: [
    {
      source: '/api/*',
      regexp: '^/api/(.*)',
      locale: false,
      has: [
        { type: 'header', key: 'Authorization', value: 'Bearer Token' },
        { type: 'query', key: 'userId', value: '123' },
      ],
      missing: [{ type: 'cookie', key: 'session', value: 'active' }],
    },
  ],
}
```

Configured matchers:

1. MUST start with `/`
2. Can include named parameters: `/about/:path` matches `/about/a` and `/about/b` but not `/about/a/c`
3. Can have modifiers on named parameters (starting with `:`): `/about/:path*` matches `/about/a/b/c` because `*` is _zero or more_. `?` is _zero or one_ and `+` _one or more_
4. Can use regular expression enclosed in parenthesis: `/about/(.*)` is the same as `/about/:path*`

Read more details on [path-to-regexp](https://github.com/pillarjs/path-to-regexp#path-to-regexp-1) documentation.

> **Good to know**:
>
> - The `matcher` values need to be constants so they can be statically analyzed at build-time. Dynamic values such as variables will be ignored.
> - For backward compatibility, Next.js always considers `/public` as `/public/index`. Therefore, a matcher of `/public/:path` will match.

## Params

### `request`

When defining Middleware, the default export function accepts a single parameter, `request`. This parameter is an instance of `NextRequest`, which represents the incoming HTTP request.

```tsx filename="middleware.ts" switcher
import type { NextRequest } from 'next/server'

export function middleware(request: NextRequest) {
  // Middleware logic goes here
}
```

```js filename="middleware.js" switcher
export function middleware(request) {
  // Middleware logic goes here
}
```

> **Good to know**:
>
> - `NextRequest` is a type that represents incoming HTTP requests in Next.js Middleware, whereas [`NextResponse`](#nextresponse) is a class used to manipulate and send back HTTP responses.

## NextResponse

The `NextResponse` API allows you to:

- `redirect` the incoming request to a different URL
- `rewrite` the response by displaying a given URL
- Set request headers for API Routes, `getServerSideProps`, and `rewrite` destinations
- Set response cookies
- Set response headers

<AppOnly>

To produce a response from Middleware, you can:

1. `rewrite` to a route ([Page](/docs/app/api-reference/file-conventions/page) or [Route Handler](/docs/app/api-reference/file-conventions/route)) that produces a response
2. return a `NextResponse` directly. See [Producing a Response](#producing-a-response)

> **Good to know**: For redirects, you can also use `Response.redirect` instead of `NextResponse.redirect`.

</AppOnly>

<PagesOnly>

To produce a response from Middleware, you can:

1. `rewrite` to a route ([Page](/docs/pages/building-your-application/routing/pages-and-layouts) or [Edge API Route](/docs/pages/building-your-application/routing/api-routes)) that produces a response
2. return a `NextResponse` directly. See [Producing a Response](#producing-a-response)

</PagesOnly>

## Execution order

Middleware will be invoked for **every route in your project**. Given this, it's crucial to use [matchers](#matcher) to precisely target or exclude specific routes. The following is the execution order:

1. `headers` from `next.config.js`
2. `redirects` from `next.config.js`
3. Middleware (`rewrites`, `redirects`, etc.)
4. `beforeFiles` (`rewrites`) from `next.config.js`
5. Filesystem routes (`public/`, `_next/static/`, `pages/`, `app/`, etc.)
6. `afterFiles` (`rewrites`) from `next.config.js`
7. Dynamic Routes (`/blog/[slug]`)
8. `fallback` (`rewrites`) from `next.config.js`

## Runtime

Middleware defaults to using the Edge runtime. As of v15.5, we have support for using the Node.js runtime. To enable, in your middleware file, set the runtime to `nodejs` in the `config` object:

```js highlight={2} filename="middleware.js" switcher
export const config = {
  runtime: 'nodejs',
}
```

```ts highlight={2} filename="middleware.ts" switcher
export const config = {
  runtime: 'nodejs',
}
```

> **Note**: This feature is not yet recommended for production use. Therefore, Next.js will throw an error unless you are using the next@canary release instead of the stable release.

## Advanced Middleware flags

In `v13.1` of Next.js two additional flags were introduced for middleware, `skipMiddlewareUrlNormalize` and `skipTrailingSlashRedirect` to handle advanced use cases.

`skipTrailingSlashRedirect` disables Next.js redirects for adding or removing trailing slashes. This allows custom handling inside middleware to maintain the trailing slash for some paths but not others, which can make incremental migrations easier.

```js filename="next.config.js"
module.exports = {
  skipTrailingSlashRedirect: true,
}
```

```js filename="middleware.js"
const legacyPrefixes = ['/docs', '/blog']

export default async function middleware(req) {
  const { pathname } = req.nextUrl

  if (legacyPrefixes.some((prefix) => pathname.startsWith(prefix))) {
    return NextResponse.next()
  }

  // apply trailing slash handling
  if (
    !pathname.endsWith('/') &&
    !pathname.match(/((?!\.well-known(?:\/.*)?)(?:[^/]+\/)*[^/]+\.\w+)/)
  ) {
    return NextResponse.redirect(
      new URL(`${req.nextUrl.pathname}/`, req.nextUrl)
    )
  }
}
```

`skipMiddlewareUrlNormalize` allows for disabling the URL normalization in Next.js to make handling direct visits and client-transitions the same. In some advanced cases, this option provides full control by using the original URL.

```js filename="next.config.js"
module.exports = {
  skipMiddlewareUrlNormalize: true,
}
```

```js filename="middleware.js"
export default async function middleware(req) {
  const { pathname } = req.nextUrl

  // GET /_next/data/build-id/hello.json

  console.log(pathname)
  // with the flag this now /_next/data/build-id/hello.json
  // without the flag this would be normalized to /hello
}
```

## Examples

### Conditional Statements

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

export function middleware(request: NextRequest) {
  if (request.nextUrl.pathname.startsWith('/about')) {
    return NextResponse.rewrite(new URL('/about-2', request.url))
  }

  if (request.nextUrl.pathname.startsWith('/dashboard')) {
    return NextResponse.rewrite(new URL('/dashboard/user', request.url))
  }
}
```

```js filename="middleware.js" switcher
import { NextResponse } from 'next/server'

export function middleware(request) {
  if (request.nextUrl.pathname.startsWith('/about')) {
    return NextResponse.rewrite(new URL('/about-2', request.url))
  }

  if (request.nextUrl.pathname.startsWith('/dashboard')) {
    return NextResponse.rewrite(new URL('/dashboard/user', request.url))
  }
}
```

## Using Cookies

Cookies are regular headers. On a `Request`, they are stored in the `Cookie` header. On a `Response` they are in the `Set-Cookie` header. Next.js provides a convenient way to access and manipulate these cookies through the `cookies` extension on `NextRequest` and `NextResponse`.

1. For incoming requests, `cookies` comes with the following methods: `get`, `getAll`, `set`, and `delete` cookies. You can check for the existence of a cookie with `has` or remove all cookies with `clear`.
2. For outgoing responses, `cookies` have the following methods `get`, `getAll`, `set`, and `delete`.

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

export function middleware(request: NextRequest) {
  // Assume a "Cookie:nextjs=fast" header to be present on the incoming request
  // Getting cookies from the request using the `RequestCookies` API
  let cookie = request.cookies.get('nextjs')
  console.log(cookie) // => { name: 'nextjs', value: 'fast', Path: '/' }
  const allCookies = request.cookies.getAll()
  console.log(allCookies) // => [{ name: 'nextjs', value: 'fast' }]

  request.cookies.has('nextjs') // => true
  request.cookies.delete('nextjs')
  request.cookies.has('nextjs') // => false

  // Setting cookies on the response using the `ResponseCookies` API
  const response = NextResponse.next()
  response.cookies.set('vercel', 'fast')
  response.cookies.set({
    name: 'vercel',
    value: 'fast',
    path: '/',
  })
  cookie = response.cookies.get('vercel')
  console.log(cookie) // => { name: 'vercel', value: 'fast', Path: '/' }
  // The outgoing response will have a `Set-Cookie:vercel=fast;path=/` header.

  return response
}
```

```js filename="middleware.js" switcher
import { NextResponse } from 'next/server'

export function middleware(request) {
  // Assume a "Cookie:nextjs=fast" header to be present on the incoming request
  // Getting cookies from the request using the `RequestCookies` API
  let cookie = request.cookies.get('nextjs')
  console.log(cookie) // => { name: 'nextjs', value: 'fast', Path: '/' }
  const allCookies = request.cookies.getAll()
  console.log(allCookies) // => [{ name: 'nextjs', value: 'fast' }]

  request.cookies.has('nextjs') // => true
  request.cookies.delete('nextjs')
  request.cookies.has('nextjs') // => false

  // Setting cookies on the response using the `ResponseCookies` API
  const response = NextResponse.next()
  response.cookies.set('vercel', 'fast')
  response.cookies.set({
    name: 'vercel',
    value: 'fast',
    path: '/',
  })
  cookie = response.cookies.get('vercel')
  console.log(cookie) // => { name: 'vercel', value: 'fast', Path: '/' }
  // The outgoing response will have a `Set-Cookie:vercel=fast;path=/test` header.

  return response
}
```

### Setting Headers

You can set request and response headers using the `NextResponse` API (setting _request_ headers is available since Next.js v13.0.0).

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

export function middleware(request: NextRequest) {
  // Clone the request headers and set a new header `x-hello-from-middleware1`
  const requestHeaders = new Headers(request.headers)
  requestHeaders.set('x-hello-from-middleware1', 'hello')

  // You can also set request headers in NextResponse.next
  const response = NextResponse.next({
    request: {
      // New request headers
      headers: requestHeaders,
    },
  })

  // Set a new response header `x-hello-from-middleware2`
  response.headers.set('x-hello-from-middleware2', 'hello')
  return response
}
```

```js filename="middleware.js" switcher
import { NextResponse } from 'next/server'

export function middleware(request) {
  // Clone the request headers and set a new header `x-hello-from-middleware1`
  const requestHeaders = new Headers(request.headers)
  requestHeaders.set('x-hello-from-middleware1', 'hello')

  // You can also set request headers in NextResponse.next
  const response = NextResponse.next({
    request: {
      // New request headers
      headers: requestHeaders,
    },
  })

  // Set a new response header `x-hello-from-middleware2`
  response.headers.set('x-hello-from-middleware2', 'hello')
  return response
}
```

> **Good to know**: Avoid setting large headers as it might cause [431 Request Header Fields Too Large](https://developer.mozilla.org/docs/Web/HTTP/Status/431) error depending on your backend web server configuration.

### CORS

You can set CORS headers in Middleware to allow cross-origin requests, including [simple](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#simple_requests) and [preflighted](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#preflighted_requests) requests.

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

const allowedOrigins = ['https://acme.com', 'https://my-app.org']

const corsOptions = {
  'Access-Control-Allow-Methods': 'GET, POST, PUT, DELETE, OPTIONS',
  'Access-Control-Allow-Headers': 'Content-Type, Authorization',
}

export function middleware(request: NextRequest) {
  // Check the origin from the request
  const origin = request.headers.get('origin') ?? ''
  const isAllowedOrigin = allowedOrigins.includes(origin)

  // Handle preflighted requests
  const isPreflight = request.method === 'OPTIONS'

  if (isPreflight) {
    const preflightHeaders = {
      ...(isAllowedOrigin && { 'Access-Control-Allow-Origin': origin }),
      ...corsOptions,
    }
    return NextResponse.json({}, { headers: preflightHeaders })
  }

  // Handle simple requests
  const response = NextResponse.next()

  if (isAllowedOrigin) {
    response.headers.set('Access-Control-Allow-Origin', origin)
  }

  Object.entries(corsOptions).forEach(([key, value]) => {
    response.headers.set(key, value)
  })

  return response
}

export const config = {
  matcher: '/api/:path*',
}
```

```jsx filename="middleware.js" switcher
import { NextResponse } from 'next/server'

const allowedOrigins = ['https://acme.com', 'https://my-app.org']

const corsOptions = {
  'Access-Control-Allow-Methods': 'GET, POST, PUT, DELETE, OPTIONS',
  'Access-Control-Allow-Headers': 'Content-Type, Authorization',
}

export function middleware(request) {
  // Check the origin from the request
  const origin = request.headers.get('origin') ?? ''
  const isAllowedOrigin = allowedOrigins.includes(origin)

  // Handle preflighted requests
  const isPreflight = request.method === 'OPTIONS'

  if (isPreflight) {
    const preflightHeaders = {
      ...(isAllowedOrigin && { 'Access-Control-Allow-Origin': origin }),
      ...corsOptions,
    }
    return NextResponse.json({}, { headers: preflightHeaders })
  }

  // Handle simple requests
  const response = NextResponse.next()

  if (isAllowedOrigin) {
    response.headers.set('Access-Control-Allow-Origin', origin)
  }

  Object.entries(corsOptions).forEach(([key, value]) => {
    response.headers.set(key, value)
  })

  return response
}

export const config = {
  matcher: '/api/:path*',
}
```

<AppOnly>

> **Good to know:** You can configure CORS headers for individual routes in [Route Handlers](/docs/app/api-reference/file-conventions/route#cors).

</AppOnly>

### Producing a response

You can respond from Middleware directly by returning a `Response` or `NextResponse` instance. (This is available since [Next.js v13.1.0](https://nextjs.org/blog/next-13-1#nextjs-advanced-middleware))

```ts filename="middleware.ts" switcher
import type { NextRequest } from 'next/server'
import { isAuthenticated } from '@lib/auth'

// Limit the middleware to paths starting with `/api/`
export const config = {
  matcher: '/api/:function*',
}

export function middleware(request: NextRequest) {
  // Call our authentication function to check the request
  if (!isAuthenticated(request)) {
    // Respond with JSON indicating an error message
    return Response.json(
      { success: false, message: 'authentication failed' },
      { status: 401 }
    )
  }
}
```

```js filename="middleware.js" switcher
import { isAuthenticated } from '@lib/auth'

// Limit the middleware to paths starting with `/api/`
export const config = {
  matcher: '/api/:function*',
}

export function middleware(request) {
  // Call our authentication function to check the request
  if (!isAuthenticated(request)) {
    // Respond with JSON indicating an error message
    return Response.json(
      { success: false, message: 'authentication failed' },
      { status: 401 }
    )
  }
}
```

### Negative matching

The `matcher` config allows full regex so matching like negative lookaheads or character matching is supported. An example of a negative lookahead to match all except specific paths can be seen here:

```js filename="middleware.js"
export const config = {
  matcher: [
    /*
     * Match all request paths except for the ones starting with:
     * - api (API routes)
     * - _next/static (static files)
     * - _next/image (image optimization files)
     * - favicon.ico, sitemap.xml, robots.txt (metadata files)
     */
    '/((?!api|_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)',
  ],
}
```

You can also bypass Middleware for certain requests by using the `missing` or `has` arrays, or a combination of both:

```js filename="middleware.js"
export const config = {
  matcher: [
    /*
     * Match all request paths except for the ones starting with:
     * - api (API routes)
     * - _next/static (static files)
     * - _next/image (image optimization files)
     * - favicon.ico, sitemap.xml, robots.txt (metadata files)
     */
    {
      source:
        '/((?!api|_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)',
      missing: [
        { type: 'header', key: 'next-router-prefetch' },
        { type: 'header', key: 'purpose', value: 'prefetch' },
      ],
    },

    {
      source:
        '/((?!api|_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)',
      has: [
        { type: 'header', key: 'next-router-prefetch' },
        { type: 'header', key: 'purpose', value: 'prefetch' },
      ],
    },

    {
      source:
        '/((?!api|_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)',
      has: [{ type: 'header', key: 'x-present' }],
      missing: [{ type: 'header', key: 'x-missing', value: 'prefetch' }],
    },
  ],
}
```

### `waitUntil` and `NextFetchEvent`

The `NextFetchEvent` object extends the native [`FetchEvent`](https://developer.mozilla.org/docs/Web/API/FetchEvent) object, and includes the [`waitUntil()`](https://developer.mozilla.org/docs/Web/API/ExtendableEvent/waitUntil) method.

The `waitUntil()` method takes a promise as an argument, and extends the lifetime of the Middleware until the promise settles. This is useful for performing work in the background.

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

export function middleware(req: NextRequest, event: NextFetchEvent) {
  event.waitUntil(
    fetch('https://my-analytics-platform.com', {
      method: 'POST',
      body: JSON.stringify({ pathname: req.nextUrl.pathname }),
    })
  )

  return NextResponse.next()
}
```

### Unit testing (experimental)

Starting in Next.js 15.1, the `next/experimental/testing/server` package contains utilities to help unit test middleware files. Unit testing middleware can help ensure that it's only run on desired paths and that custom routing logic works as intended before code reaches production.

The `unstable_doesMiddlewareMatch` function can be used to assert whether middleware will run for the provided URL, headers, and cookies.

```js
import { unstable_doesMiddlewareMatch } from 'next/experimental/testing/server'

expect(
  unstable_doesMiddlewareMatch({
    config,
    nextConfig,
    url: '/test',
  })
).toEqual(false)
```

The entire middleware function can also be tested.

```js
import { isRewrite, getRewrittenUrl } from 'next/experimental/testing/server'

const request = new NextRequest('https://nextjs.org/docs')
const response = await middleware(request)
expect(isRewrite(response)).toEqual(true)
expect(getRewrittenUrl(response)).toEqual('https://other-domain.com/docs')
// getRedirectUrl could also be used if the response were a redirect
```

## Platform support

| Deployment Option                                                   | Supported         |
| ------------------------------------------------------------------- | ----------------- |
| [Node.js server](/docs/app/getting-started/deploying#nodejs-server) | Yes               |
| [Docker container](/docs/app/getting-started/deploying#docker)      | Yes               |
| [Static export](/docs/app/getting-started/deploying#static-export)  | No                |
| [Adapters](/docs/app/getting-started/deploying#adapters)            | Platform-specific |

Learn how to [configure Middleware](/docs/app/guides/self-hosting#middleware) when self-hosting Next.js.

## Version history

| Version   | Changes                                                                                       |
| --------- | --------------------------------------------------------------------------------------------- |
| `v15.2.0` | Middleware can now use the Node.js runtime (experimental)                                     |
| `v13.1.0` | Advanced Middleware flags added                                                               |
| `v13.0.0` | Middleware can modify request headers, response headers, and send responses                   |
| `v12.2.0` | Middleware is stable, please see the [upgrade guide](/docs/messages/middleware-upgrade-guide) |
| `v12.0.9` | Enforce absolute URLs in Edge Runtime ([PR](https://github.com/vercel/next.js/pull/33410))    |
| `v12.0.0` | Middleware (Beta) added                                                                       |