That ^ at the start of your middleware matcher is the entire problem.

In Next.js middleware, the config.matcher field does not accept arbitrary regular expressions in the same way many developers expect. If you copy a regex-style route pattern and begin it with ^, Next.js will reject it because matchers are parsed as route match patterns, not raw anchored regex strings.

Understanding the Root Cause

The confusion comes from the way Next.js documents and processes middleware matchers. A matcher may look regex-like, but it is not treated as a full free-form JavaScript regular expression. Internally, Next.js validates and compiles the matcher using its own routing rules.

That means patterns starting with ^ fail because:

• config.matcher expects a path-based matcher syntax, not a raw regex literal.
• The leading ^ is a regex anchor, but the matcher engine already assumes route matching semantics from the path root.
• Next.js validates matcher input before runtime, so invalid syntax causes a build or startup error instead of silently failing.

For example, this is the kind of configuration that triggers the issue:

export const config = {
  matcher: ['^/api/(.*)'],
}

Even though that looks valid in a normal regex context, it is not valid here. The matcher should be written as a route pattern:

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

Or, if you are using a negative lookahead pattern based on official middleware-style route syntax, it should still begin with /, not ^.

Step-by-Step Solution

The fix is straightforward: rewrite the matcher using Next.js-supported path syntax.

1. Identify the invalid matcher

If your middleware.ts contains something like this, the leading anchor is the issue:

export const config = {
  matcher: ['^/about/(.*)', '^/dashboard/(.*)'],
}

2. Replace regex-style anchors with route-based patterns

Convert those entries into supported matcher values:

export const config = {
  matcher: ['/about/:path*', '/dashboard/:path*'],
}

3. Use the documented middleware exclusion pattern correctly

A common middleware example excludes internal and static routes. If you are adapting that logic, make sure the pattern starts with /:

export const config = {
  matcher: ['/((?!api|_next/static|_next/image|favicon.ico).*)'],
}

Notice that this uses / as the route prefix. Do not rewrite it like this:

export const config = {
  matcher: ['^/((?!api|_next/static|_next/image|favicon.ico).*)'],
}

That version is invalid because the matcher parser does not allow the regex anchor at the beginning.

4. Verify your middleware file

A working example looks like this:

import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'

export function middleware(request: NextRequest) {
  return NextResponse.next()
}

export const config = {
  matcher: ['/dashboard/:path*', '/settings/:path*'],
}

5. Restart the dev server

After updating matcher syntax, restart next dev or your production build process so the new configuration is revalidated cleanly.

npm run dev

If you are using another package manager:

yarn dev

pnpm dev

6. Test the actual route coverage

Check that your middleware now runs only for the intended routes:

• /dashboard
• /dashboard/team
• /settings/profile

If you want to confirm official matcher behavior, review the Next.js middleware matcher documentation.

Common Edge Cases

1. Mixing route syntax and raw regex assumptions

Developers often assume matcher behaves exactly like new RegExp(). It does not. Some advanced-looking patterns are supported, but the overall string still has to satisfy Next.js route matcher constraints.

2. Forgetting the leading slash

This is another easy mistake. Matchers should generally start with /.

export const config = {
  matcher: ['dashboard/:path*'],
}

The safer version is:

export const config = {
  matcher: ['/dashboard/:path*'],
}

3. Incorrect exclusion patterns

If you are excluding _next assets or API routes, a malformed negative lookahead can cause middleware to run on static assets unexpectedly, which may break images, CSS, or performance-critical requests.

Use a tested pattern such as:

export const config = {
  matcher: ['/((?!api|_next/static|_next/image|favicon.ico).*)'],
}

4. Expecting middleware on files that are never matched

If your route is nested or uses dynamic segments, a too-specific matcher may miss child paths. For example:

export const config = {
  matcher: ['/dashboard'],
}

This may not cover deeper routes the way you expect. Use:

export const config = {
  matcher: ['/dashboard/:path*'],
}

5. Version-specific documentation confusion

Examples may vary between Next.js versions or documentation sections. If a snippet appears regex-heavy, keep in mind that middleware matcher input is still validated as a route pattern string. When in doubt, prefer the documented examples exactly as shown in the official docs rather than converting them into classic regex form.

FAQ

Can I use regular expressions in config.matcher?

You can use patterns that include regex-like behavior supported by Next.js, but config.matcher is not the same as passing a raw JavaScript regex string. A leading ^ is not accepted because the matcher must remain a valid Next.js route matcher.

Why does the official example look regex-like if ^ is invalid?

Because Next.js supports a constrained matcher syntax that can include constructs like negative lookaheads. That does not mean every normal regex token is allowed in every position. The string must still begin as a valid route path, typically with /.

What should I use instead of ^/foo/(.*)?

Use a route matcher such as /foo/:path*. It is clearer, officially supported, and maps directly to how middleware routing works in Next.js.

The practical takeaway is simple: middleware matchers must start like paths, not like regexes. If your pattern begins with ^, rewrite it to begin with / and use Next.js matcher syntax such as :path* or a valid documented exclusion pattern.