User-Agent

User-Agent

The User-Agent header is used by client applications to identify themselves, much like the Server header for servers. Its value is the product name and possibly a comment describing the client application.

This header's format is somewhat free-form. Its value varies from client product to product and release to release. This header sometimes even contains information about the machine on which the client is running.

As with the Server header, don't be surprised if older proxy or gateway applications insert what amounts to a Via header in the User-Agent header itself.