Hey everyone,

I’m hitting a bit of a wall with mTLS in Fiddler Everywhere. My logs are showing the following error repeatedly: "[Error] [Fiddler] The server [domain] requested a client certificate, but no client certificate was available."

The Situation:

• I have my client certificate ready (as a .pfx, no password).

• My setup involves several subdomains, specifically:

  • appdata.mydomain.com

  • apps-boost-global.mydomain.com

• They all use the SAME certificate.

The Problem: I can’t find a clear, definitive path on where to save these files so Fiddler Everywhere actually "sees" and picks them up. I've seen mentions of Documents\FiddlerCore, .fiddler\ClientCerts, and others, but none seem to trigger the handshake correctly.

My Questions:

1. What is the exact directory path Fiddler Everywhere uses for client certificates in the latest version?

2. Since I’m using the same cert for multiple domains, do I need to duplicate and rename the file for every single subdomain (e.g., hostname.pfx), or is there a way to map one cert to multiple hosts in the UI/Settings?

3. Does the file extension matter (should I use .pfx, .p12, or rename to .cer)?

   
   

I am trying to capture the traffic while launching Bloons TD 1 but it doesn't appear on fiddler

I have a C# rule script in fiddler classic, which convert the http request form-data body from "key1=value1" to json {"key1": "value1"}

I am trying to migrate to fiddler everywhere, but I have no idea how to achieve this in fiddler everywhere, where's rule script in fiddler everywhere?

Fiddler classic doesn't capture anything because there's a security software in my case that always changes the proxy setting if I change it for Fiddler.

Fiddler Anywhere feels like a hack. It's only good for capturing when launching a browser from within it.
There's no functionality to capture http requests that come out from apps running on the machine. No capturing from apps that host browsers like webview.

Please make a tool that can capture requests from any app. See httpdebugger.com as an example. The tool need not depend on a proxy.

Receiving this error: 

[2025-09-25 16:50:27:054] [Error] [Fiddler] !SecureClientPipeDirect failed: Org.BouncyCastle.Tls.TlsFatalAlertReceived illegal_parameter(47) for pipe (CN=*.facebook.com, O=Progress Telerik Fiddler, OU=Created by http://www.fiddler2.com)

I have a user that reported issues trying to use "Fiddler Everywhere" after upgrading their OS:

"I updated from windows 10 to windows 11...Fiddler Everywhere was working last week when I was using on Windows 10. After upgrading, I tried to use it again today and cannot establish a remote connection to monitor traffic from a mobile device. I noticed when I first opened Fiddler I received a windows firewall notification. The option to "allow" was greyed out and I could only close the prompt. I am assuming the problem with connecting is related to the firewall but these seem to be managed by the organization. Please help allow traffic through Fiddler to assist in my debugging workflows."

I don't use Fiddler, and my team doesn't have internal documentation on troubleshooting Fiddler.  I enclosed some screen captures of what the user has sent us.  He is an Administrator on his Windows laptop, but I noticed some duplicate entries in his Windows Firewall that are grayed out, likely to Group Policy.

Any assistance would be greatly appreciated.

Hi,
I'm unable to access DuckDuckGo with Fiddler Everywhere. I can connect to DuckDuckGo without Fiddler. I think it's because DuckDuckGo detects Fiddler. Other possibilities are that the Fiddler certificate also supports unsafe TLS 1.0 and TLS 1.1, and their server ignores the request, but I'm not sure. Can you connect to DuckDuckGo, or is this issue exclusive to me? Thanks

This is what I received in the response. 

Delete my account

I need to capture URLs for Oracle SmartView logins. I saw some video for fiddler classic to setup. but can you help me to do the same set up ln enterprise.

https://youtu.be/syUoIw8N2WQ

pls provide the steps for enterprise:

 

When I try to analyse the requests on Yahoo Finance, I see different results when requesting from a browser with Fiddler turned on compared to the same request when Fiddler is turned off. I also tried different capture methods (System Proxy, Network Capture and Browser), but the same occurs. If I use this url:

 

https://query1.finance.yahoo.com/v8/finance/chart/IVV?events=capitalGain%7Cdiv%7Csplit&formatted=true&includeAdjustedClose=true&interval=1d&period1=0&period2=1747180800&symbol=IVV&userYfid=true&lang=en-US&region=US

 

Opening this url in a Chrome tab with Fiddler turned off, everything works fine (HTTP 200 response). Wih Fiddler turned on, however, the site responds with a HTTP 429 code (Too Many Requests).

 

Why this is happening?