I recently upgraded to the latest version of Fiddler Classic and the application no longer starts up.  It crashes silently (no error message pop-up) and the Fiddler window is never displayed. 

Running on Windows 10. 

The Windows Application Log shows the following:

Faulting application name: Fiddler.exe, version: 5.0.20245.10105, time stamp: 0x670fd121
Faulting module name: KERNELBASE.dll, version: 10.0.19041.5198, time stamp: 0xd1eefc71
Exception code: 0xc06d007e
Fault offset: 0x000000000003b699
Faulting process id: 0x3e54
Faulting application start time: 0x01db636fee33f9f3
Faulting application path: C:\Users\XXXXX\AppData\Local\Programs\Fiddler\Fiddler.exe
Faulting module path: C:\Windows\System32\KERNELBASE.dll
Report Id: 8bf8de2d-211a-4462-93da-34efc27e8337
Faulting package full name: 
Faulting package-relative application ID: 

I have tried uninstalling and re-installing but the results are the same.

Any ideas for how this can be fixed?  Thanks.

While playing around with windows 10 and looking for ways to ensure it will Shut the F*** up and break up with M$ I noticed that the various privacy violating services seam to respect the proxy configuration in the internet options.

So I installed fiddler on my test VM and enabled SSL decryption.

For some requests like windows update that seamed to work just fine,

but for the interesting telemetry once, it fails with error 408, for example requests to watson.telemetry.microsoft.com

The textView window says "The request body did not contain the specified number of bytes. Got 0, expected 1.359"

So I think its a bug with fiddler (or the lack of support for some protocol version) rather than M$ cooking up their own super secret SSL replacement.

So it would be great if the makers of fiddler could fiddle around a bit with this issue and solve it please :)

Hi,

We are unable to execute any with Power apps  in Desktop application when Fiddler Trace is active, it keeps loading forever and after closing Fiddler it works fine.  Could you please advise?

Thanks in advance.

Victor Pontes

Hey,

since tonight (nothing changed on my Side I believe), randomly some Websites stopped to appear on Fiddler Everywhere MacOS in Capture Mode.

When I surf around / facebook / mmo-champion etc. (just example pages) they appear as Connect Tunnel opened but no content is seen.

So the Websites no longer get shown in the Traffic Window, just the Connect Tunnels.

I tried to uninstall Fiddler Everywhere, Resetting Configs by removing the Transprancy Proxy from MacOS but nothing seems to help, is there any instance I can check, why some websites randomly disappear and not coming back on MacOS? 

Do I need to "listen" on more Ports or so?

I am using Windows 10 (it may work fine on Windows 11).

I was unable to capture the link below using Fiddler Classic and Fiddler Everywhere (trial version).

I think Fiddler Everywhere does not support TLS 1.3 successfully in Windows 10. If there is a way to force the connection to TLS 1.3 in Fiddler Everywhere, it may work, but I could not find such a setting.

I have confirmed that 3rd party network capturing tools successfully capture the link below, but why only Fiddler Classic and Everywhere fail? If Windows 10 does not fully support TLS 1.3, then 3rd party capturing tools should not work either, but since 3rd party programs work perfectly, I am wondering why this symptom only occurs in Fiddler.

https://smartstore.naver.com/powermtb/products/6236194845

Why does the POST request custom reply file not work?

GET asks him to be able to reply normally with a local file！

fiddler-everywhere-5.21.0.AppImage runs successfully on a Fedora 37 workstation. On a Fedora 41 workstation it throws a System.TypeInitializationException and reports " Fiddler.WebUi is tampered" and fails to start the server.:

09:08:37.489 › Trying to start server at port [16197].
09:08:37.617 › Server error log during start: Unhandled exception. 
09:08:37.632 › Server error log during start: System.TypeInitializationException: The type initializer for '<Module>' threw an exception.
 ---> System.Exception: Fiddler.WebUi is tampered.
   at MaoFcf2Vq4taIANM6n.hIDAYxH6DWLHIthQgC.zSLipEDdx()
   at .cctor()
   --- End of inner exception stack trace ---

The checksum on the AppImage file is the same on both FC37 and FC41 workstations. It fails on a clean FC41 installation as well as on another system that was upgraded from FC38 to FC41. Full "script" log attached. Am I missing some preparation or is this a bug?

Hello,

Pretty new to Fiddler, I'm using Fiddler Everywhere 5.21.0 .

What I'm trying to achieve is to replace the status code of a call to an identity server with 401, but just once.

I've created a following rule

Conditions:

When any of these conditions are met specific number of times: 1

URL Contains [Identity Server]/connect/token

Actions:

Update status code: 401

However, live traffic shows that when a /connect/token request is sent out, its status code is 200.

Only when I increase

When any of these conditions are met specific number of times: 2

A /connect/token request (a singular one, based on the Live Traffic view) will have its status code replaced to 401.

Why is that the case? Does the Live View actually filter out some traffic?

Thanks for bearing with my silly questions.

How is possible select a target (e.g. an opened application) ?

I mean that in the classic fiddler is possible to drag the "target" icon over any app or browser, which you like to inspect

Thank you