It takes input a http log file. The User-Agent string format is currently specified by Section 14.43 of RFC 2616 (HTTP/1.1) . The format of the User-Agent string in HTTP is a list of product tokens (keywords) with optional comments. For example if your product were called WikiBrowser, your user agent string might be WikiBrowser/1.0 Gecko/1.0. The "most important" product component is listed first.