---
title: "HTTP Message Signatures: definition | Agent Ready Crawlers"
description: "HTTP Message Signatures: RFC 9421, a standard for signing selected components of an HTTP message, carried in Signature and Signature-Input headers."
canonical: https://agentreadycrawlers.com/glossary/http-message-signatures
site: "Agent Ready Crawlers"
last_updated: 2026-11-04
section: "Glossary"
---

# HTTP Message Signatures: definition | Agent Ready Crawlers

> HTTP Message Signatures: RFC 9421, a standard for signing selected components of an HTTP message, carried in Signature and Signature-Input headers.

Source: https://agentreadycrawlers.com/glossary/http-message-signatures
Site: Agent Ready Crawlers
Last reviewed: 2026-11-04

Glossary

# HTTP Message Signatures

In short

RFC 9421: a standard for signing selected components of an HTTP message, carried in Signature and Signature-Input headers. Web Bot Auth is a profile of it. A verifier library for RFC 9421 is the starting point for the checks in the guide. Example: OpenAI tells site owners to verify ChatGPT Cloud browser requests according to RFC 9421.

## Definition

RFC 9421: a standard for signing selected components of an HTTP message, carried in Signature and Signature-Input headers. Web Bot Auth is a profile of it.

## Sourced example

OpenAI tells site owners to verify ChatGPT Cloud browser requests according to RFC 9421. [Source](https://help.openai.com/en/articles/11845367-chatgpt-agent-allowlisting), read 2026-11-04.

## How it shows up here

A verifier library for RFC 9421 is the starting point for the checks in the guide.

-   [Verify Web Bot Auth signatures](https://agentreadycrawlers.com/guides/verify-web-bot-auth/)
-   [Web Bot Auth](https://agentreadycrawlers.com/glossary/web-bot-auth/)

Previous: [HTTP 402 Payment Required](https://agentreadycrawlers.com/glossary/http-402/). Next: [IP range JSON](https://agentreadycrawlers.com/glossary/ip-range-json/). [All 41 terms](https://agentreadycrawlers.com/glossary/).

## Sources

-   [ChatGPT Work's Cloud browser allowlisting](https://help.openai.com/en/articles/11845367-chatgpt-agent-allowlisting) read 2026-11-04

Last reviewed 2026-11-04