---
title: "User-agent string: definition | Agent Ready Crawlers"
description: "User-agent string: The User-Agent HTTP header a client sends. Anyone can copy it, so operators pair it with IP lists, reverse DNS or signatures."
canonical: https://agentreadycrawlers.com/glossary/user-agent-string
site: "Agent Ready Crawlers"
last_updated: 2026-11-04
section: "Glossary"
---

# User-agent string: definition | Agent Ready Crawlers

> User-agent string: The User-Agent HTTP header a client sends. Anyone can copy it, so operators pair it with IP lists, reverse DNS or signatures.

Source: https://agentreadycrawlers.com/glossary/user-agent-string
Site: Agent Ready Crawlers
Last reviewed: 2026-11-04

Glossary

# User-agent string

In short

The User-Agent HTTP header a client sends. Anyone can copy it, so operators pair it with IP lists, reverse DNS or signatures. Each profile prints the string the operator documents. For the 23 rows with no robots.txt token the field says so. Example: OAI-SearchBot sends a Chrome-like string ending "compatible; OAI-SearchBot/1.4; +https://openai.com/searchbot". Related: Tokens versus user-agent strings and GPTBot profile.

## Definition

The User-Agent HTTP header a client sends. Anyone can copy it, so operators pair it with IP lists, reverse DNS or signatures.

## Sourced example

OAI-SearchBot sends a Chrome-like string ending "compatible; OAI-SearchBot/1.4; +https://openai.com/searchbot". [Source](https://platform.openai.com/docs/bots), read 2026-11-04.

## How it shows up here

Each profile prints the string the operator documents. For the 23 rows with no robots.txt token the field says so.

-   [Tokens versus user-agent strings](https://agentreadycrawlers.com/guides/tokens-versus-user-agent-strings/)
-   [GPTBot profile](https://agentreadycrawlers.com/crawlers/gptbot/)

Previous: [Training crawler](https://agentreadycrawlers.com/glossary/training-crawler/). Next: [User-triggered fetcher](https://agentreadycrawlers.com/glossary/user-triggered-fetcher/). [All 41 terms](https://agentreadycrawlers.com/glossary/).

## Sources

-   [Overview of OpenAI Crawlers](https://platform.openai.com/docs/bots) read 2026-11-04

Last reviewed 2026-11-04