---
title: Filtering query parameters
description: Learn how to filter query parameters in your Middleware.
url: /kb/guide/filter-query-parameters
canonical_url: "https://vercel.com/kb/guide/filter-query-parameters"
published: 2025-11-03
last_updated: 2025-11-11
authors: DX Team
related:
  - /docs/routing-middleware
  - /docs/routing-middleware/api
install_vercel_plugin: npx plugins add vercel/vercel-plugin
---

The following example shows how to filter query parameters in your Middleware.

Your `middleware` file should be placed at the root of your project. If you are using the `src` directory, the file should be placed in the `src` directory.

```js
import { NextResponse } from 'next/server';

const allowedParams = ['allowed'];

export const config = {
  matcher: '/',
};

export default function middleware(request) {
  const url = request.nextUrl;
  let changed = false;

  url.searchParams.forEach((_, key) => {
    if (!allowedParams.includes(key)) {
      url.searchParams.delete(key);
      changed = true;
    }
  });

  // Avoid infinite loop by only redirecting if the query
  // params were changed
  if (changed) {
    return NextResponse.rewrite(url);
  }
}
```
```ts
import { NextResponse } from 'next/server';
import type { NextRequest } from 'next/server';

const allowedParams = ['allowed'];

export const config = {
  matcher: '/',
};

export default function middleware(request: NextRequest) {
  const url = request.nextUrl;
  let changed = false;

  url.searchParams.forEach((_, key) => {
    if (!allowedParams.includes(key)) {
      url.searchParams.delete(key);
      changed = true;
    }
  });

  // Avoid infinite loop by only redirecting if the query
  // params were changed
  if (changed) {
    return NextResponse.rewrite(url);
  }
}
```

## More resources

- [Middleware](/docs/routing-middleware)
  
- [Middleware API](/docs/routing-middleware/api)