About PAC Explained

PAC Explained is a free, open-source reference for writing and debugging Proxy Auto-Configuration (PAC) files. For years, findproxyforurl.com was the place network engineers turned to for a clear explanation of every PAC helper function. When it went offline it left a real gap — the remaining documentation is scattered across MDN, decade-old MSDN articles, and forum threads.

This site was built to fill that gap in one place: a complete function reference, best practices, security guidance, WPAD auto-discovery, performance notes, and a live in-browser tester that evaluates your PAC file without sending anything to a server.

PAC Explained is built and maintained by abskulaity (abskulaity.net, GitHub @bunnis) — a developer who has spent a fair amount of time wrangling corporate proxy configs and wanted the reference that was missing. It is an independent project, not affiliated with Mozilla, Google, or any proxy vendor.

The site is open source. Anyone can read the code, suggest corrections, or contribute improvements on GitHub. If a section is wrong or incomplete, a pull request or issue is the fastest way to fix it.

Every function description, example, and caveat on this site is written by hand and checked against authoritative sources and real-world behaviour, including:

• The original Netscape PAC specification and Microsoft's WinHTTP/WPAD documentation.
• The MDN PAC reference.
• The pacparser engine, used to verify how functions actually evaluate.
• Hands-on testing in Chrome, Firefox, and Edge to document browser-specific quirks.

The goal is accuracy over volume. If you spot an error, please get in touch — corrections are always welcome.

The site is free and ad-supported. If it saved you time, you can buy me a coffee — it's appreciated but never required. For questions, corrections, or anything else, see the contact page.