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.

When I attempt to browse to one of my company's websites with Fiddler running, I get the following error on the CONNECT:

fiddler.network.https> HTTPS handshake to site.mycompany.com failed. System.IO.IOException Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. < An existing connection was forcibly closed by the remote host

Fiddler is running under the administrator account and can access most other HTTPS sites (ie, Outlook, Facebook, other company sites).  Things I've tried:

• Installing the Fiddler certificate under Local Machine (that compounded the problem, couldn't access the Telerik site then)
• Tried running IE as administrator
• Added CONFIG.oAcceptedServerHTTPSProtocols = System.Security.Authentication.SslProtocols.Ssl3; in the Main function in Fiddler script.

Any ideas?

Hi

I recently downloaded the fiddler classic and it's crash when opening. And i already tried almost ways to fix it. And the log show that the MSVCR80.dll module error when the fiddler classic started.And  I Already reinstall the Microsoft Visual C++ 2005 Redistributable but it doesn't work. Could you please help to fix the crash？

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:

 

Whenever I try to open  3 Patti Lucky, the screen either freezes or stays completely blank for a long time. Sometimes it just loads halfway and suddenly disappears without showing anything. On other occasions, I notice the screen going black, and after a few seconds, it automatically closes without any message or warning. Even after trying multiple times, the same issue continues. I have restarted my device, made sure my internet is working fine, and even cleared stored data to see if something changes. I also made sure my device has enough storage and is updated, but the problem still doesn't go away. It feels like something is stopping the process from running fully, especially during the initial stage.

This issue started recently, and it wasn’t like this before. Everything used to work fine, and I used it daily without any problem. Now, it’s difficult to continue because nothing loads properly. I hope this problem gets fixed soon, or at least there is a proper solution or update available. If anyone else is facing the same thing or has found a way to fix it, please let me know.

Hello,

I have two questions regarding Fiddler Classic, and I would appreciate your help.

1) Cloudflare blocking error

When I try to load either of the two websites below through Fiddler Classic, I receive the following Cloudflare error message: "Sorry, you have been blocked." Please see the screen shot attached.

https://www.gurufocus.com
https://et3arraf.com

Both websites load fine when Fiddler is not active. Over time, I’ve encountered the same issue with several other sites as well — the two above are just recent examples. It seems this error has become more frequent lately.

Do you know why this happens? Is there any way to bypass or prevent this issue?

2) TLS 1.3 support in Fiddler Classic

Could you please provide an update regarding the implementation of TLS 1.3 in Fiddler Classic? Is it still under development, or has the upgrade been officially discontinued?

No recent news here: https://feedback.telerik.com/fiddler/1584209-support-tls-1-3-now-that-net-framework-does

Please note that I’d consider switching to Fiddler Everywhere, but I’m currently relying on a large script that only works with the Classic version, since scripting isn’t yet supported in Everywhere.

Thank you in advance!

Best regards,
Alex

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?

HI All,

I get the following error when trying to open .saz files.  Do you know what is happening and if I get other .saz files recorded, is there a particular setting I should look for? 


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Awww, Fiddlesticks!
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Fiddler has encountered an unexpected problem. If you believe this is a bug in Fiddler, please copy this message by hitting CTRL+C, and submit a bug report at http://www.telerik.com/forums/fiddler.

Input string was not in a correct format.

Type: System.FormatException
Source: mscorlib
   at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)

   at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)

   at Fiddler.Session.TestComparator(Object )

   at Fiddler.Session.LoadMetadata(Stream strmMetadata)


Fiddler v5.0.20253.3311 (x64 AMD64) [.NET 4.0.30319.42000 on Microsoft Windows NT 10.0.22631.0] 
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OK   
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