I am trying v5.0.20253.3311 for .NET 4.6.2.

When [File]-[Save]-[All Sessions] and input filename of Session Archive(*.saz) and [Save], 

I see the following dialog: 

Failed to save Session Archive. Could not load file or assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51' or one of its dependencies. The system cannot find the file specified.

Please let me know how to solve this problem.

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. 

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

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? 


---------------------------
Awww, Fiddlesticks!
---------------------------
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] 
---------------------------
OK   
---------------------------

I keep getting this warning and as soon I click, I get it back. I think one of the security apps is monitoring and locking down the proxy server setting in Windows. I am running Fiddler as an admin and manually setting the proxy server but my setting is instantly removed.
It seems I can't use network sniffers that depend on certain proxy server settings.

Does Fiddler Anywhere suffer from the same issue?

Today after upgrade Fiddler Classic to new version we got compilation error for our custom rules.

Fiddler version:

v5.0.20253.3311 for .NET 4.6.2
Built: Monday, March 31, 2025

64-bit AMD64, VM: 63.0mb, WS: 114.0mb
.NET 4.8 WinNT 10.0.22631.0

I don't see in release notes anything about FiddlerScript changes. So what need to be added now to resolve this issue?

Hi there, I've used Fiddler occasionally for years, but am new to Fiddler Anywhere. I want to use Fiddler to accurately time page load times of my Dynamics 365 CRM system. I used to do this by filtering on the URL of my CRM system, clearing the traffic window, loading a page, clicking Ctrl+A in the traffic window to highlight all the sessions, and then reading off the total time from start to end (currently shown as the Max Duration figure in the Overview Window).

This method is working for me some of the time currently, but only for about one in three page loads that I test. The problem seems to be related to the "Client Connected" time which sometimes doesn't reset for each page load. In the screenshot below, you can see that I clicked the link in my browser at 11:54:12, but the system is providing a timing which starts at 11:53:59 as the Client Connected time. It incorrectly tells me the session lasted 13.67s when it actually only began at the Client Begin Request time and took less than a second to complete.

Is there a way to tell Fiddler Anywhere to ignore the Client Connected time and measure from Client Begin Request instead? Alternatively, can I force my browser to start a new connection each time I load a page (which it seems to sometimes, if I've been idle for a minute or so)?

Any help greatly appreciated,

Best wishes,

Tony