# About findproxyforurl.net

Source: https://findproxyforurl.net/about/ · updated 2026-10-06

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](https://findproxyforurl.net/check/) 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](https://findproxyforurl.net/generate/) and the [builders for security service edge
  vendors](https://findproxyforurl.net/generate/sse/) write files that pass that test;
- the reference explains [`FindProxyForURL`](https://findproxyforurl.net/findproxyforurl/), every [helper
  function](https://findproxyforurl.net/functions/), the [engines](https://findproxyforurl.net/engines/) and their [differences](https://findproxyforurl.net/engines/differences/),
  [WPAD](https://findproxyforurl.net/wpad/) and the [rule catalogue](https://findproxyforurl.net/rules/).

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](https://findproxyforurl.net/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.