middleware.js

The middleware.js|ts file is used to write 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.

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*',
}

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.

// 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 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.

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.

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 documentation.

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.

import type { NextRequest } from 'next/server'
 
export function middleware(request: NextRequest) {
  // Middleware logic goes here
}

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

To produce a response from Middleware, you can:

1. rewrite to a route (Page or Edge API Route) that produces a response
2. return a NextResponse directly. See Producing a Response

Execution order

Middleware will be invoked for every route in your project. Given this, it's crucial to use matchers 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 v15.2 (canary), we have experimental support for using the Node.js runtime. To enable, add the flag to your next.config file:

import type { NextConfig } from 'next'
 
const nextConfig: NextConfig = {
  experimental: {
    nodeMiddleware: true,
  },
}
 
export default nextConfig

Then in your middleware file, set the runtime to nodejs in the config object:

export const config = {
  runtime: 'nodejs',
}

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.

module.exports = {
  skipTrailingSlashRedirect: true,
}

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.

module.exports = {
  skipMiddlewareUrlNormalize: true,
}

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

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))
  }
}

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.

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
}

Setting Headers

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

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
}

CORS

You can set CORS headers in Middleware to allow cross-origin requests, including simple and preflighted requests.

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*',
}

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)

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 }
    )
  }
}

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:

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:

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 object, and includes the 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.

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.

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.

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

Learn how to configure Middleware when self-hosting Next.js.

Version history