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Test a PAC file

A PAC script decides, URL by URL, which proxy to use. The only way to know what it does for your URL is to run it.

What a PAC script is

A proxy auto-configuration file is a JavaScript function, FindProxyForURL(url, host), that returns DIRECT or a list of proxies for each URL (MDN). Companies use one to send internal hosts around the proxy and everything else through it. Browsers and many Windows programs follow the script the machine names. Command-line tools usually do not, and read proxy variables instead - one reason the browser and a script disagree.

Run the script your machine uses

certdoctor https://api.example.com/

L2 finds the script your machine names, fetches it, runs it in a sandbox for this URL, and shows its answer next to every other place that names a proxy: the environment variables, the Windows Internet Settings and the WinHTTP settings. When they disagree, you see which program follows which.

Run any script by its address

certdoctor https://api.example.com/ --pac-url http://wpad.example.com/proxy.pac

--pac-url asks about a script whether or not anything on the machine names it. On Linux, where there is no system-wide PAC setting, it is the way to ask. Run it once per URL you care about: a script often sends different hosts different ways.

What the answer means

• A proxy - this URL goes through it. certdoctor then asks the proxy whether it wants credentials, and names a 407.
• DIRECT - this URL goes straight to the server.
• No usable answer - reported as UNKNOWN with the reason, never as DIRECT, because guessing “no proxy” would send you looking in the wrong place.