While Fiddler isn't designed for use in a service, it is possible, and enables a few interesting scenarios.
For example it can launch on system startup, and removes the need for a user to be logged in.
- Establish the account that will install Fiddler. This user needs to be at least a standard user, but the privileges can be dropped back to restricted when install is done.
- Log in as FiddlerUser. Install Fiddler, make sure that it works and settings, rules etc are as desired, when logged in as that user. Log out as FiddlerUser.
- Logged in as an admin: follow the directions to set up a user app as a service given in http://support.microsoft.com/kb/137890. (Note for this you will need instsrv.exe and srvany.exe from the Windows Server 2003 Resource Kit. If you don’t have them download from here. They work under XP also). Call the service FiddlerService or something like that.
- To adjust settings on the service go to MyComputer > Manage > Services and Applications > Services. Find your FiddlerService in the services list and double click. Check the Log on tab; uncheck Local System Account and check This Account. Now select the account under which you installed Fiddler. You’ll have to enter the FiddlerUser password. This part is important, since Fiddler loads rules from the MyDocuments folder of the user in whose context it runs.
- You can adjust other settings, such as manual or automatic launch of the service in the General tab, and any actions you want on failure in the Recovery tab.
- Restart and verify that Fiddler works. Note that you might have to wait for all the services to get started. I’ve noticed that it can be a minute or more after the login prompt appears. In the task manager you should see the service running
You will almost certainly want to use the -quiet command line parameter when launching Fiddler, to prevent modal dialogs from appearing.