The Web tool shows you what your web browser's "User-Agent" header for your HTTP requests. The "User-Agent" is acting on behalf of a user.
Most Web browsers use a User-Agent value as follows: Mozilla/[version] ([system and browser information]) [platform] ([platform details]) [extensions]. For example, Chrome has used the following: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.152 Safari/537.36