"proxy_pac_rb" is a gem to compress, lint and parse proxy auto-config files. It comes with a cli program, some rack middlewares and can be used from within ruby scripts as well. "proxy_pac_rb" uses a JavaScript runtime to evaulate a proxy auto-config file the same way a browser does to determine what proxy (if any at all) should a program use to connect to a server. You must install on of the supported JavaScript runtimes: therubyracer or therubyrhino