---
description: Supported header name and value formats for response header modifications.
title: Format of HTTP response header names and values
image: https://developers.cloudflare.com/og-docs.png
---

[Skip to content](#main-content)

> 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.

# Format of HTTP response header names and values

Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://e8aee267.previews.developers.cloudflare.com/rules/transform/response-header-modification/reference/header-format/index.md)|[Agent setup](https://e8aee267.previews.developers.cloudflare.com/agent-setup/)

The **name** of the HTTP response header you want to set or remove can only contain:

* Alphanumeric characters: `a`\-`z`, `A`\-`Z`, and `0`\-`9`
* The following special characters: `-` and `_`

The **value** of the HTTP response header you want to set can only contain:

* Alphanumeric characters: `a`\-`z`, `A`\-`Z`, and `0`\-`9`
* The following special characters: `` _ :;.,\/"'?!(){}[]@<>=-+*#$&`|~^% ``

The **length** of the HTTP response header can be a maximum of 4 KB (\~4,096 characters).

Was this helpful?

YesNo

## On this page

[![](https://e8aee267.previews.developers.cloudflare.com/_astro/logo.te5VL_aD.svg)Docs](https://e8aee267.previews.developers.cloudflare.com/)

```json
{"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/rules/transform/response-header-modification/reference/header-format/#page","headline":"Format of HTTP response header names and values · Cloudflare Rules docs","description":"Supported header name and value formats for response header modifications.","url":"https://developers.cloudflare.com/rules/transform/response-header-modification/reference/header-format/","inLanguage":"en","image":"https://developers.cloudflare.com/og-docs.png","dateModified":"2026-08-24","publisher":{"@type":"Organization","name":"Cloudflare","url":"https://www.cloudflare.com/"},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"},"keywords":["Headers"]}
```