---
description: Reference for request header modification rules.
title: Reference
image: https://developers.cloudflare.com/og-docs.png
---

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# Reference

Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/rules/transform/request-header-modification/reference/index.md)|[Agent setup](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/agent-setup/)

This section contains reference information for Request Header Transform Rules.

* [Format of HTTP request header names and values](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/rules/transform/request-header-modification/reference/header-format/)
* [Available fields and functions](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/rules/transform/request-header-modification/reference/fields-functions/)
* [API parameter reference](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/rules/transform/request-header-modification/reference/parameters/)

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