Pactester is a tool to test proxy
auto-configuration (PAC) files. PAC files are 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. Pactester resolves this issue by
simulating browser behavior.