---
title: API parameter reference
description: Configurable parameters for request header modification rules.
image: https://developers.cloudflare.com/core-services-preview.png
---

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### Tags

[ Headers ](https://developers.cloudflare.com/search/?tags=Headers)[ Request modification ](https://developers.cloudflare.com/search/?tags=Request%20modification) 

# API parameter reference

To set an HTTP request header via API, set the following parameters in the `action_parameters` field:

* **operation**: `set`
* Include one of the following parameters to define a static or dynamic value:  
   * **value**: Specifies a static value for the HTTP request header.  
   * **expression**: Specifies the expression that defines a value for the HTTP request header.

To remove an HTTP request header via API, set the following parameter in the `action_parameters` field:

* **operation**: `remove`

For step-by-step instructions, refer to [Create a request header transform rule via API](https://developers.cloudflare.com/rules/transform/request-header-modification/create-api/).

## Static header value parameters

The full syntax of the `action_parameters` field to define a static HTTP request header value is the following:

```

"action_parameters": {

  "headers": {

    "<HEADER_NAME>": {

      "operation": "set",

      "value": "<URI_PATH_VALUE>"

    }

  }

}


```

## Dynamic header value parameters

The full syntax of the `action_parameters` field to define a dynamic HTTP request header value using an expression is the following:

```

"action_parameters": {

  "headers": {

    "<HEADER_NAME>": {

      "operation": "set",

      "expression": "<EXPRESSION>"

    }

  }

}


```

Note

Check the [available fields and functions](https://developers.cloudflare.com/rules/transform/request-header-modification/reference/fields-functions/) you can use in an expression.

## Header removal parameters

The full syntax of the `action_parameters` field to remove an HTTP request header is the following:

```

"action_parameters": {

  "headers": {

    "<HEADER_NAME>": {

      "operation": "remove"

    }

  }

}


```

## Different header modifications in the same rule

The same rule can modify different HTTP request headers using different operations (set or remove a header). For example, a single rule can set the value of a header and remove a different header. The syntax of such a rule could be the following:

```

"action_parameters": {

  "headers": {

    "<HEADER_NAME_1>": {

      "operation": "set",

      "value": "<HEADER_VALUE_1>"

    },

    "<HEADER_NAME_2>": {

      "operation": "remove"

    }

  }

}


```

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