---
language: en
title: "User agent"
description: "A user agent identifies the client software; in HTTP, the header declares information about it. It helps analyze traffic but does not, by itself, authenticate the visitor."
canonical: "https://tropk.ai/en/resources/glossary/user-agent"
last_modified: "2026-10-12T16:11:35.267Z"
---

# User agent

Reviewed on 2026-10-06.

## What it means

A user agent is client software that initiates a communication, such as a browser or [crawler](/en/resources/glossary/crawler). In access analytics, the term also commonly refers to the HTTP User-Agent header, which declares information about that software. The HTTP specification allows product identifiers, versions, and comments; this declaration helps the server interpret the incoming request.

## Why it matters for marketing

For marketing and [SEO](/en/resources/glossary/seo), the header allows teams to separate groups of visits and investigate content delivery failures. A team might observe that requests declaring themselves as a particular bot receive a different response from visitors. This helps guide technical investigation, but attributing all such requests to the provider based on the name alone can distort the diagnosis.

## Example in practice

Imagine a portal that logs requests with the text [Googlebot](/en/resources/glossary/googlebot) in the header, all receiving a 403 error in a search section. Before requesting that they be allowed through, the analyst asks for the source addresses to be checked using the method documented by Google. The team decides to adjust the rule only for requests whose origin has been verified, while keeping a record of the diagnosis.

## How to apply or verify

To verify a visit, collect the URL, time, complete header, source address, and server response. Compare the declared identity with the operator's current documentation and apply its published validation method. For Google, the documentation includes checks using IP ranges and DNS names, as well as the reported header.

## Important distinctions

The User-Agent header does not provide cryptographic proof of identity or purpose and can be imitated by another client. It is also not identical to the token used in the User-agent line of [robots.txt](/en/resources/glossary/robots-txt). [Google-Extended](/en/resources/glossary/google-extended), for example, is a control token with no dedicated HTTP header. Product, access client, and content usage preference must be considered separately.

## Sources and references

- [RFC 9110: HTTP Semantics — User-Agent](<https://www.rfc-editor.org/rfc/rfc9110.html#name-user-agent>) — IETF
- [List of Google's common crawlers](<https://developers.google.com/crawling/docs/crawlers-fetchers/google-common-crawlers>) — Google
- [Verify requests from Google crawlers and fetchers](<https://developers.google.com/crawling/docs/crawlers-fetchers/verify-google-requests>) — Google

## Continue a leitura

- [Crawler purpose category](</en/resources/glossary/crawler-purpose-category>)
- [Crawler](</en/resources/glossary/crawler>)
- [robots.txt](</en/resources/glossary/robots-txt>)

## About the author

[Vinicius Pacheco](</en/team/vinicius-pacheco>)

Responsible for Tropk’s technical content, focusing on crawling, indexing, structured data, and agent access to content.

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