Questions on Fiddler Forum

1 answer

12 views

Already saw the post about adding the column via "Customized Columns"

So I did:

Customized Columns>Collection>Session Timers

then

Timer Name>ClientBeginRequest

However it only shows the time and does not show the date. I need the date for when something particular happens with my browser connections, and I am not in front of my computer every minute.

Fiddler Classic

answered on 30 Oct 2026

1 answer

9 views

Request: Fiddler Classic Old Version Installers and SHA256 Hashes for CNAS Testing

Dear Telerik Support Team,

We are an ISO/IEC 17025 (CNAS) accredited software testing laboratory in China. We need a specific old version of Fiddler Classic for controlled HTTP/HTTPS traffic capture and interface testing in our accredited test activities.

The latest public download page only provides the newest version, and the required historical build is no longer available publicly.

Could you please provide the official installer download link for Fiddler Classic version:

5.0.20262

5.0.20261

5.0.20253

And please also provide the **official SHA256 checksum** of this installer file for integrity verification.

Important notes for our quality system:

1. This installer will be used as a calibrated test tool under our CNAS quality management system (CNAS-CL01-A019:2018).

2. We need official evidence to prove the package is the original, unmodified release from Telerik.

3. We will archive your reply, download link and checksum record in our tool control file, and perform local hash validation before putting the tool into formal testing use.

4. Fiddler Classic is freeware, we confirm we will comply with its end-user license agreement.

If you cannot share the file directly, please let us know the official channel we can obtain this authentic historical release.

Thank you very much for your support.

Best regards,

linyan,Qian

Fiddler Classic

answered on 28 Oct 2026

2 answers

34 views

Fiddler Classic and everywhere blocked by CloudFront

Tried multiple browsers but always receive from booking.com when inspecting traffic:

HTTP/1.1 403 Forbidden
Server: CloudFront
Date: Mon, 19 Oct 2026 19:55:37 GMT
Content-Type: text/html
Content-Length: 919
Connection: keep-alive
X-Cache: Error from cloudfront
Via: 1.1 fc20c1482245d494719df97cc96116e0.cloudfront.net (CloudFront)
X-Amz-Cf-Pop: PHX52-P3
X-Amz-Cf-Id: _nmq3w2vKtiW70wXoSzzLJMBavMsrHTE7odnkCrEVoQgzrdV_iQ7iA==
Strict-Transport-Security: max-age=63072000; includeSubDomains; preload
Accept-CH: ECT

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML><HEAD><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<TITLE>ERROR: The request could not be satisfied</TITLE>
</HEAD><BODY>
<H1>403 ERROR</H1>
<H2>The request could not be satisfied.</H2>
<HR noshade size="1px">
Request blocked.
We can't connect to the server for this app or website at this time. There might be too much traffic or a configuration error. Try again later, or contact the app or website owner.
<BR clear="all">
If you provide content to customers through CloudFront, you can find steps to troubleshoot and help prevent this error by reviewing the CloudFront documentation.
<BR clear="all">
<HR noshade size="1px">
<PRE>
Generated by cloudfront (CloudFront)
Request ID: _nmq3w2vKtiW70wXoSzzLJMBavMsrHTE7odnkCrEVoQgzrdV_iQ7iA==
</PRE>
<ADDRESS>
</ADDRESS>
</BODY></HTML>

Any work around?

Fiddler Classic

answered on 21 Oct 2026

12 answers

2.8K+ views

Firefox 36.0 breaks Fiddler HTTPS decryption

There seems to be a problem with Firefox version 36.0 onwards with the Fiddler HTTPS decryption option. The instructions at http://www.telerik.com/blogs/configuring-firefox-for-fiddler used to work for adding the Fiddler root certificate so that Firefox will trust the certificates that Fiddler issues. This is also the only way to trust Fiddler for HSTS (HTTP Strict Transport Security) sites because Firefox doesn't allow adding regular "exceptions" for those sites.

After updating Firefox, I found that the Fiddler root CA no longer works to connect to the HTTPS websites. Firefox gives a "ssl_error_bad_cert_domain" error. An example of what this looks like is:

www.google.com uses an invalid security certificate. The certificate is only valid for *.google.com (Error code: ssl_error_bad_cert_domain)

So this appears to be failing to match the wildcard domain (*.google.com) to the website (www.google.com) and rejecting the certificate as a result.

I tried downgrading back to different Firefox versions, and found that 35.0.1 is the last one that seems to work properly for the Fiddler HTTPS decryption, with 36.0 breaking this functionality.

I first reported this issue on Mozilla support: https://support.mozilla.org/en-US/questions/1090724

Is this a known bug / break in compatibility? Has anyone reported this issue yet and is there a known workaround?

Fiddler Classic

answered on 13 Oct 2026

1 answer

33 views

MCP Server not supporting SSL

Claude Desktop will not let me enter an MCP server with our https

Jay

Fiddler Everywhere

answered on 02 Oct 2026

1 answer

26 views

Unsaved Changes dialog when closing Fiddler Anywhere after opening a HAR file and changing column layout

Columns I find useful like the timestamp and duration are missing from the default, so I have to add them when I open a HAR. Since version 8.0.0 I have started to get a dialog box when I try to close Fiddler Anywhere:

Title: You have unsaved Changes!
Are you sure you want to quit?
You have unsaved changes that will be lost in Filters.

I have not added filters to this HAR file, and I have closed all other HAR files and all other saved sessions.

I never actually want to save anything related to the files I open. I don't care if any filters I've added are unsaved, I don't want to be prompted. I just want the program to close when I click the close button.

Is there any way to disable this dialog?

Fiddler Everywhere

Windows

answered on 29 Sep 2026

2 answers

875 views

blocking fiddler from interfering with certain apps

hi, i am new to fiddler and i only use it to set up some private servers for games, and it ends up logging data from all my active apps even chrome, is there a way to stop fiddler from touching chrome/other apps while it only works with my games? even when i am on discord i have a hard time on calls because fiddler is on and i have to turn it off to make the voice call work smoothly without issues, is there a way i can block fiddler from interfering with discord?

Fiddler Classic

answered on 13 Aug 2026

1 answer

112 views

[Solved] Clarification on Fiddler Classic commercial use during and after the transition period

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.

Fiddler Classic

Windows

updated question on 05 Aug 2026

1 answer

64 views

Feature Request: Stop after #### Sessions

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?

Extensions and Customization

Fiddler Classic

Windows

answered on 03 Aug 2026

3 answers

1.3K+ views

If no FiddlerScript in Everywhere, will you at least continue to support Fiddler Classic?

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

Fiddler Classic

Fiddler Everywhere

updated answer on 03 Aug 2026