Access and anti-bot
User agent
Also called: User-Agent header
The request header in which a client identifies its software, such as a browser name and version.
In practice
Only one of many signals. A mismatched user agent is one of the fastest ways to get flagged.
What the header tells a server
A User-Agent request header identifies the client software making an HTTP request. Its text can include a product name, version and platform details, although the information may be reduced or inaccurate. It is useful context for troubleshooting, not strong proof of a particular person, browser or device. A client-supplied label should not be treated as an authentication credential.
Example: diagnosing different responses
Suppose a monitoring client receives a simplified page while a browser shows a richer layout. Record the request context, including the User-Agent, alongside the response and rendering behaviour. The header may be relevant, but cookies, location, JavaScript execution and other factors can also change what appears. Do not conclude that changing one header reproduces a full browser environment.
What it does not establish
A User-Agent value does not grant permission to access a source or establish the identity of a crawler. Keep access policy and authentication decisions separate from client identification. When testing your own site, compare the actual rendered content and supported features instead of relying solely on browser-name detection. For public specifications and examples, consult the linked header reference.
Further reading
Rendering, fingerprinting, challenges and residential egress in 190 locales are handled inside the Import.io platform, and blocked requests are not billed.
How Import.io reaches protected sites →