! Note: Fiddler registry settings are subject to change at any time, and should generally be set using only the Fiddler user-interface. In particular, the settings should not be set, or directly replied upon, by Fiddler Extensions.
HKEY_CURRENT_USER\Software\Microsoft\Fiddler2
Older Settings
AutoProxyLogon - Default: False. Controls whether Fiddler will permit WinHTTP to log in to the proxy server to obtain the proxy configuration script. Set to True if you have an autoproxy script that Fiddler isn't using.
CaptureFTP - Default: False. True causes Fiddler to register as the proxy for FTP traffic. Note, Fiddler does not itself support FTP, so if configured as the proxy for FTP, you must either satisfy all requests using the AutoResponder, or have a FTP-capable proxy server upstream.
CheckForISA - Default: True. True causes Fiddler to check for an ISA configuration file to determine if the ISA Firewall client is installed and may interfere with Fiddler.
DebugSpew - Default: False. True causes Fiddler to spew debug information to the system debug console.
ExclusivePort - Default: missing. True forces Fiddler's listening socket to set the ExclusiveAddressUse flag rather than relying on the operating system default.
GatewayUsername - Default: missing. Set to the username Fiddler should use when performing proxy authentication for the version check.
GatewayPassword - Default: missing. Set to the password Fiddler should use when performing proxy authentication for the version check.
LoadExtensions - Default: True. Controls whether Fiddler loads FiddlerExtensions.
LoadInspectors - Default: True. Controls whether Fiddler loads Inspector extensions.
LoadScript - Default: True. Controls whether FiddlerScript engine is loaded.
ReverseProxyForPort - Default: missing. Controls what port Fiddler is acting as a reverse proxy for.
TextEditor - Default: "notepad.exe". Controls what external editor Fiddler launches to edit text files.
UseEventLogForExceptions - Default: False. Controls whether Fiddler will log exceptions to the system event log.
UserPath - Default: missing. Set to the fully qualified path under which Fiddler should save and load its configuration settings.
Introduced in v2.2.4.1
HookWithPAC - Default: False. True causes Fiddler to set its PAC script file as the system proxy rather than registering directly. This allows Fiddler to capture http://localhost and http://127.0.0.1 traffic without special tricks.
MakeCertParamsEE - Default: "-pe -ss my -n \"{0}{1}\" -sky exchange -in {2} -is my -eku 1.3.6.1.5.5.7.3.1 -cy end -a sha1". This is the string passed to MakeCert.exe when Fiddler is creating the HTTPS traffic interception end-entity certificates.
MakeCertParamsRoot - Default: "-ss my -n \"{0}{1}\" -eku 1.3.6.1.5.5.7.3.1 -r -cy authority -a sha1". This is the string passed to MakeCert.exe when Fiddler is creating the HTTPS traffic interception root certificate.
MakeCertRootCN - Default: "DO_NOT_TRUST_FiddlerRoot"
MakeCertSubjectO - Default: ", O=DO_NOT_TRUST, OU=Created by http://www.fiddler2.com"
ShowDefaultClientCertificateNeededPrompt - Default: True. Set to False to prevent warning messages requesting that you move a client certificate into the Fiddler application folder.
UseXceedDecompress - Default: False. True causes Fiddler to use the Xceed libraries for decompression of HTTP traffic as it did in earlier versions. The switch to System.IO libraries enables proper decompression of malformed GZIP content, as sent by Bing.com and some other popular sites.