A Proxy Auto-Configuration file (PAC file) is a file which contains a function,FindProxyForURL(), which is used by the browser to determine whether requests (including HTTP, HTTPS, and FTP) should go directly to the destination or if they need to be forwarded through a web proxy server.

function FindProxyForURL(url, host) {  // …}ret = FindProxyForURL(url, host);

SeeProxy Auto-Configuration (PAC) file for details about how these are used and how to create new ones.

See also

• PAC on Wikipedia
• Proxy Auto-Configuration file on MDN