WebPAC: A Proxy auto-config file generator

What’s a .PAC file?

PAC file allows your to create custom rules for proxy settings in an intranet. All workstations can have their proxy settings centralized in one file and you can set different proxies, depending on IP address, URL or network.

Under the hood, it is basically a JavaScript file (but with .pac extension) loaded onto browsers. When the browser is requesting a new URL, the JavaScript function FindProxyForURL() runs, and based on the function’s return value, a proxy is set. Read more