About findproxyforurl.net

findproxyforurl.net is a free, independent tool and reference for proxy auto-configuration (PAC) files. It is named after the one function every PAC file defines, FindProxyForURL(url, host).

What it is for

PAC files decide, for every web request in an organisation, whether traffic goes to a proxy or straight to the internet. They are small, rarely reviewed and evaluated slightly differently by every browser. A mistake usually does not show up as an error. Traffic quietly bypasses the proxy, or every request waits for DNS.

The site exists to make those mistakes visible before users or attackers find them:

• the online PAC file tester runs a proxy.pac or wpad.dat in Chromium, Firefox and pacparser engine profiles and rates it from A+ to F;
• the PAC file generator and the builders for security service edge vendors write files that pass that test;
• the reference explains FindProxyForURL, every helper function, the engines and their differences, WPAD and the rule catalogue.

It is written for network and security engineers, proxy and SSE administrators, and anyone who inherited a PAC file.

How it works

The checker runs in your browser. Your PAC file is evaluated in a sandboxed worker on a separate origin. For the rating only anonymised facts about the code are sent, and the original file is never sent or stored. There are no cookies, no analytics and no third-party scripts on this site.

Every statement about how an engine behaves names its evidence (engine source code, vendor documentation, a lab run or practitioner knowledge) and the date it was checked. Unverified claims are labelled as such. The details are in the methodology.

Who runs it

findproxyforurl.net is an independent project, not affiliated with any browser or proxy vendor. Vendor names appear only to describe compatibility. The site is free to use and is provided as is, without warranty. Verify results in your own environment before you roll out a PAC file.