Following guide online to swap out the old max speed with the new max speed but i'm using a mac whereas most people used fiddler classic on windows and i'm not sure whether I put the values in the correct places within the rule.  Anyone spot my noob mistake ?  Seems like many people had success so I know it's possible and my phone with the app making the API calls is connected properly to Fiddler that's not the problem. Please any help is so appreciated ! Thanks so much

websocket message garbled

Hello, for some tests, I'd like to use Fiddler to route through the corporate proxy network and, in a specific case, process requests/responses directly with mitmproxy scripts (because Fiddler Everywhere doesn't yet offer the same functionality as FC).

So I connect Fiddler to mitmproxy by setting the gateway proxy to mitmproxy listening at localhost:9090.

But it seems that Fiddler doesn't respect this setting. It always routes through the internet normally.
Even if I intentionally configure the wrong proxy port, the connection persists.

What should I do? Maybe I got wrong something??

 

I'm using Fiddler in Linux and already added certificates of Fiddler and mitmproxy to the system (actually i'm using the same one).

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?

I am running 

Progress Telerik Fiddler Classic
v5.0.20253.3311 for .NET 4.6.2
Built: Monday, March 31, 2025
64-bit AMD64, VM: 74.0mb, WS: 145.0mb
.NET 4.8 WinNT 10.0.26100.0

 

When trying to import a net-export JSON file it fails with

---------------------------

Failed to import NetLog
---------------------------
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.

Could not load type 'JSONParseErrors' from assembly 'Fiddler, Version=5.0.20253.3311, Culture=neutral, PublicKeyToken=null'.

Type: System.TypeLoadException
Source: FiddlerImportNetlog
   at FiddlerImportNetlog.NetlogImporter..ctor(StreamReader oSR, List`1 listSessions, EventHandler`1 evtProgressNotifications)

   at FiddlerImportNetlog.NetLogFormatImport.ImportSessions(String sFormat, Dictionary`2 dictOptions, EventHandler`1 evtProgressNotifications)


Fiddler v5.0.20253.3311 (x64 AMD64) [.NET 4.0.30319.42000 on Microsoft Windows NT 10.0.26100.0] 
---------------------------
OK   
---------------------------

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?

I am running Windows 11 Home addition and a friend of mine is running Windows 10 Pro.  When I installed Fiddler Classic on my computer I was able to start monitoring API traffic with a couple setting changes.  Once I did that, everything worked fine including being able to go to various websites.

My friend installed the same version of Fiddler on his computer and immediately had issues going to websites.  I gave him all of my settings and he never could see the API traffic.  He did get a message indicating that "Do_Not_Trust Certificate was the cause of this.

Why would Fiddler work on my computer and not his?  I did not think that installing a certificate would cause this issue.  I would really appreciate any information that would help get Fiddler working for him

Thanks

Charles

I am using Fiddler Classic strictly for its FiddlerScript capabilities, and I have just learned that the Progress team no longer have any plans to add this awesome functionality to Fiddler Everywhere. This is very sad news for me, as I feel that probably Fiddler's most appreciated feature is dropped all together. I have just installed the Everywhere version, checked out its Rules tab, but I am most positive that all those hard-coded rules will not even come close to the functionality and the simplicity provided by a scripting language. The Rules tab in Everywhere may be a more easier and intuitive option for most users, but this comes at the price of loosing the flexibility and the powerful tools that only a script can provide. The web is becoming more and more complex with each day, and in order for Fiddler to stay on top of it, I believe it should give its users access to the most powerful tools available. Employing scripting capabilities is certainly one of it, if not the best one! Why restrict that?!

I would like to take this opportunity to kindly ask the design team to re-evaluate this decision of dropping this future. It sets Fiddler apart from all the other software out there, and dropping it all together would be a major downgrade for Fiddler, in my opinion. Having a Rules tab for those in need of a quick set-up, and preserving the current scripting capabilities for those looking for powerful functionality seems like the best way to go for me. With these two foundations, I have no doubt Fiddler will continue to stay relevant and grow in the years ahead.

Anyhow, in case no re-evaluation will be made and approved, I would like to know if you have any plans of dropping support/updates for Fiddler Classic in the future. This would be a second blow to all the 10 year+ Fiddler users.

I hope both versions will be offered to us for many years to come, no matter how much the web will be changing. So, please confirm if we can at least rely on Fiddler Classic, as some believe it is only a matter of time until it will be deprecated (including me). For the time being, hopefully the plans to add support for HTTP/2 and TLS 1.3 will indeed materialize (for Fiddler Classic).

If others feel like me on this whole issue, please do comment. Thank you!

Alex

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