Hello Fiddler team,

I am writing to request clarification on how commercial use of Fiddler Classic is defined following the licensing change effective 3 August 2026.

We have used Fiddler Classic for many years in software and API testing, troubleshooting, and network traffic analysis. We are currently reviewing legacy deployments and images that may still contain the product and planning the appropriate migration and compliance steps.

Could you please clarify how commercial use is assessed in the following situations?

• Does the presence of Fiddler Classic on an EC2 instance or AMI, by itself, constitute commercial use?

• Or does commercial use apply only when Fiddler Classic is launched and actively used, such as to capture API calls or other network traffic?

• How should an unused legacy AMI that still contains the installation be treated?

• What licensing or compliance steps do you recommend for deployments or images that may still contain Fiddler Classic after 17 September 2026?

A clear explanation of the applicable criteria would help us determine the appropriate migration and compliance steps. Thank you for your assistance. We look forward to your guidance.

Hi Telerik -

I need to capture a the web requests that go to an OAUTH token endpoint in order to troubleshoot a bug.

The app seldom refreshes tokens, and normally it works fine, but sometimes it gets stuck in a loop where it does it over and over and over. 

Currently, if I use the "Keep #### Sessions" combobox, once it gets stuck, I get only the last #### sessions which is not what I want.  I want the first ones so I can see what might have been different that caused it to get stuck in a loop.

Alternatively, I can keep all sessions but that crashes the PC because it uses all the RAM before I notice it when into the loop.

It would be great if, next to the "Keep: #### Sessions" drop down, there was an option to "Stop Capture after this limit."

Can you please add this feature?

Hello,

i try to read a capfile created by zscaler. But Fiddler gives a error. 
Any idea how to solve that?

Regards,

René

Hello,

i have a pcap file exported from zscaler. when reading it into fiddler classic the error attached in the screenshot is displayed.

how can i solve it?

regards,

René

Hi, i get this error on any site any browser, 

when i looked at the certificate list, i see that the certificate is expired:

i just reinstalled the last version, but the problem persists

is there any way to fix that ?

I need Fiddler to capture my call from nodejs. 

I call https://domain from nodejs like this

  import { ProxyAgent, fetch } from 'undici';
  const dispatcher = new ProxyAgent('http://127.0.0.1:8888' )
   var r2 = await fetch('https://domain', {
	method: 'POST',
	dispatcher,
	headers: {	
                 ...}
	  },
    body:  ...
  }
  );
  var r2data = await r2.json();

I can do the above call to http://domain, but when I changed to https://domain, I got the below error, any idea how do I handle this? thanks

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.