> ## Documentation Index
> Fetch the complete documentation index at: https://gcore-doc-1046.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Invalid user agent and unknown user agent

These two WAAP policies work together to identify and block requests that lack a standard user-agent parameter. If the agent is missing, this can indicate that an illegitimate client is being used.

Most browsers provide user agent information across the network to validate a client's authenticity and purpose. User agent strings typically follow this syntax:

`User-Agent: <product> / <product-version> <comment>`

Where:

* `<product>`: A product identifier—its name or development codename.

* `<product-version>`: Version number of the product.

* `<comment>`: Comments containing more details. For example, sub-product information.

<Accordion title="Example formats of generated user agents">
  This is the common format of a user agent generated by a web browser:

  `User-Agent: Mozilla/5.0 (<system-information>) <platform> (<platform-details>) <extensions>`

  The following is an example of a user agent generated by a Windows XP user browsing a website via Google Chrome:

  `Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/98.0.4758.102 Safari/537.36`

  This user agent indicates that the user is using Windows 10 (Windows NT 10.0), a 64-bit system (Win64; x64), and the latest version of Chrome (98.0.4758.102) at the time of browsing.

  `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/98.0.4758.102 Safari/537.36`

  This user agent indicates that the user is using macOS (Macintosh), specifically version 10.15.7 (Intel Mac OS X 10\_15\_7), and the latest version of Chrome (98.0.4758.102) at the time of browsing.
</Accordion>