Post by Manu Garg, Google Systems Administrator
I'm pleased to announce that we've just released pactester, a tool to test the proxy auto-configuration (PAC) files used by browsers to identify the correct proxy server for a given URL. Since the PAC file evaluation mechanism is generated inside the browser and cannot be accessed from outside, the only way to tell which proxy your browser will use for a specific URL is manual inspection of the PAC file. Unfortunately, this approach is error prone and quickly becomes impractical for large and complex PAC files. Enter pactester, which resolves this issue by simulating browser behavior.
For more on pactester, check out the project documentation.