---
description: Reference for request header modification rules.
title: Reference
image: https://developers.cloudflare.com/rules/transform/request-header-modification/reference/og.png?v=f01d592fbf6ad3da
---

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> Documentation Index  
> Fetch the complete documentation index at: https://developers.cloudflare.com/rules/llms.txt  
> Use this file to discover all available pages before exploring further.

# Reference

Last updated Apr 16, 2026|Copy as Markdown| [View as Markdown](https://developers.cloudflare.com/rules/transform/request-header-modification/reference/index.md)| [Agent setup](https://developers.cloudflare.com/agent-setup/)

This section contains reference information for Request Header Transform Rules.

- [Format of HTTP request header names and values](https://developers.cloudflare.com/rules/transform/request-header-modification/reference/header-format/)
- [Available fields and functions](https://developers.cloudflare.com/rules/transform/request-header-modification/reference/fields-functions/)
- [API parameter reference](https://developers.cloudflare.com/rules/transform/request-header-modification/reference/parameters/)

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