Last Updated: 24 May 2023 04:12 by chen
Created by: Eric
Comments: 1
Type: Feature Request

The .NET Framework has added support for TLS/1.3.

We should do the work to enable TLS/1.3 in Fiddler (it's very little additional work to add "Tls1.3" to the options dialog and the underlying code). 

Last Updated: 05 May 2023 07:24 by ADMIN

Fiddler classic uninstall after epic app & valorant online game not working some error as to come valorant error code : val 29

Epic error code : 404

Need More Info
Last Updated: 05 May 2023 07:09 by ADMIN
Created by: Michael
Comments: 1
Type: Bug Report

Fiddler would NOT allow me to save the file.  We tried this multiple times to various file locations. 

I do not have Visual Studio installed on my PC -- so I selected the latest verison in this form because it is a REQUIRED field. 

Fiddler provided the text below. 



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.


Could not find file 'C:\Users\629243897\Documents\IBMSPend on v85 debug - 2 refreshes after logon.saz'.


Type: System.IO.FileNotFoundException

Source: mscorlib

   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)


   at System.IO.FileInfo.get_Length()


   at Fiddler.frmViewer.actSaveSessionArchive(String , String
, Session[] ) in C:\Jenkins\Fiddler_Windows\workspace\Fiddler2\Fiddler.Shared\Viewer.cs:line 6808



Fiddler v5.0.20211.51073 (x64 AMD64) [.NET 4.0.30319.42000 on Microsoft Windows NT 10.0.22621.0]




Last Updated: 29 Mar 2023 08:21 by ADMIN
Created by: Eric
Comments: 0
Type: Bug Report

When sending post data, -d option needs to ensure that the data does not start with an @



BasicFormats.dll - cURLExport.cs

Last Updated: 03 Dec 2022 04:14 by Eric

As noted in the Fiddler book,

Sessions rerouted from one hostname to another using the Host Remapping tool are rendered with a light blue background in the Web Sessions list. HTTPS Sessions that have been rerouted have the X-IgnoreCertCNMismatch and X-OverrideCertCN Session Flags set to avoid raising “Certificate Name Mismatch” errors.

However, there's a bug. In the HostsFile.cs code, there's are several places that look like:

            if (oS.isTunnel) {

                oS["x-overrideCertCN"] = oS.hostname;
                oS["X-IgnoreCertCNMismatch"] = "HOSTS-Ext";

This usually works for browser traffic going through Fiddler (because the HTTPS handshake is typically conducted on the CONNECT tunnel). However, it doesn't work (and the user is spammed with cert error warnings) if the traffic is sent from Fiddler itself (e.g. via Composer or using the "Reissue requests" context menu item). 

The code should look like this:

            if (oS.isHTTPS || oS.isTunnel) {

                oS["x-overrideCertCN"] = oS.hostname;
                oS["X-IgnoreCertCNMismatch"] = "HOSTS-Ext";


Last Updated: 22 Nov 2022 16:49 by Eric

If you open use fiddler for a while (a Day or so), eventually it lock up the UI on the other monitors. It is almost as if there is an invisible dialog over the other screens. Once you kill Fiddler. its all restored again.


We have been Noticing this over the last few months.

Last Updated: 29 Aug 2022 05:36 by ADMIN

Fiddler downloads content to show on its homescreen from HTTP URLs. This is not safe because the content is rendered to the user in a WebView control and thus an attacker on the wire could replace it with malicious code or instructions that could harm the user.

Fiddler should not be using HTTP URLs for anything in this day and age.


Last Updated: 12 Aug 2022 06:32 by ADMIN

document-policy: force-load-at-top



Need More Info
Last Updated: 01 Jul 2022 19:35 by Eric

I am trying to use settings Tools -> Win8 Loopback Exemptions -> Exempt All -> Save Changes. But it is giving me some error and saving those changes. Following is the error.

Failed to set IsolationExempt AppContainers; call returned 0x57

I am blocked due to this error and cannot perform tests on my application. Pls help.


Last Updated: 23 May 2022 06:51 by ADMIN

When there's a HAR file with h3 entries, they are either misinterpreted or ignored.

I know how to fix it both in the importer/exporter DLL and in Fiddler.exe.

I can submit a correction.

Need More Info
Last Updated: 06 May 2022 11:37 by zaaz
Created by: jeriko
Comments: 2
Type: Feature Request

For now fiddler just have filter, and it not ignore traffic. Filter just hiding it.

Also Fiddler have option "Capture/Dont capture traffic" via menu File or F12. but it general for all. Also this option NOT work while the target app still use fiddler proxy.

My example problem :

I am using Nox to test MyDownloader app, while apk connect internet or requesting web data its ok to proxified by fiddler. But when I start downloading, the file is downloaded first to Fiddler cache until complete. after complete then fiddler continue request with that file response. That the problem. This also applied to all request in my PC. No problem if size just 20MB. But above 100M, 500MB, 1GB, sometime it make fiddler hang.

Also when i download file, then cancel it, fiddler still download file until complete. So to cancel that in fiddler, i need to disconnect it first.


For now, to bypass my problem i also using Proxi*fi*er filter to selecting mimetype.


Last Updated: 21 Apr 2022 22:07 by Eric

Hello! The problem is described on this link: stackoverflow


 Please add in Filter -  feature block named "Request Body" with options "Show only if request body contains", "Hide only if request body contains"

Under Review
Last Updated: 13 Apr 2022 12:21 by ADMIN
Created by: Imported User
Comments: 4
Type: Feature Request
Hi there, what's the correct way to call:



after calling these JSON methods, fiddler says:

Variable 'JSON' has not been declared


Pending Review
Last Updated: 10 Apr 2022 14:30 by Eu

I want to capture the traffic from Android Phone, and already install Root Certificate as 'System Trusted Credintials' in /system/etc/security/cacerts (renamed like '269953fb.0' by md5).

Accessing the https page, It seems to behave well in a normal application and other browser (like XBrowser, a tiny volume browser, only 1.01MB) ,and which proves that the certificate is installed correctly, but in Chrome it prompts 'NET:ERR_CERT_AUTHORITY_INVALID'. As shown, it seems that Chrome does not associate the web certificate returned by Fiddler with the root certificate already installed on the system, but I use the same installation method in Charles, it behaves well and can browse https pages normally, it seems that Charles generates a different certificate than Fiddler? I used the command

'openssl x509 -inform der -text -in /mnt/d/Users/menEu/Desktop/FiddlerRoot.cer'

to see the difference and it doesn't seem to be a huge difference (but I'm not specialized in this area)

Need More Info
Last Updated: 07 Apr 2022 05:55 by ADMIN

I've tried multiple allocation ratios and nothing solves the problem, the screen allocation ratio is 2560x1600.

Version Windows 10 Home Chinese
Version number 21H1
Installation Date ‎2021/‎12/‎25
OS Build 19043.1586
Experience Windows Feature Experience Pack 120.2212.4170.0

fiddler version :

v5.0.20211.51073 for .NET 4.6.1
Under Review
Last Updated: 29 Mar 2022 16:33 by Antonio
Created by: Bob
Comments: 2
Type: Feature Request
Could you add 'search text' function to the websocket tab?
Under Review
Last Updated: 26 Mar 2022 08:26 by Larry
In the File > Export > Export Raw Files code, there's a "Skip non-HTTP/200 responses" option. This option is designed for dumping files (either media files or files to be replayed by the AutoResponder) to a folder.

For various reasons, clients and servers often will use Range requests for media downloads, meaning that the response code for a response might be HTTP/206 instead of HTTP/200, even if the full body is present.

To enhance the file exporter, the code should look at the Content-Range response header for a HTTP/206 response. If the header is of the format:

Content-Range: bytes 0-N/N+1

Then Fiddler should treat the response as a HTTP/200 and save the body to disk.
Last Updated: 23 Mar 2022 06:25 by ADMIN

So far Fiddler says it can only import unencrypted sessions from PCAP files.

Various tools and libraries support the SSLKeylogfile environment variable and log the necessary keys.

You can either have them inside the pcapng file or in a seperate file.

It would be nice if Fiddler would accept an optional file with these keys and treated sessions with a suitable key as unencrypted.

This would make things a lot easier in the process.

Need More Info
Last Updated: 07 Mar 2022 10:17 by ADMIN


I have a connectivity issue when I run Fiddler (Progress Telerik Fiddler Web Debugger). I work behind a corporate proxy server and the server IP is changed every few hours. The change in IP is normally okay, but when I am running Fiddler with the 'Automatically Authenticate' option enabled, then Fiddler shows an error every time the proxy is changed; it shows a yellow error message suggesting "The system proxy was changed. Click to reenable capturing".

Clicking on the error in Fiddler works fine and it reconnects, but I find this frustrating because if i don't realise there was an error in fiddler and don't click it immediately then it affects my connectivity and some activities on my pc start to fail without me realising.

My suggestion is that you should let Fiddler auto-reconnect when this type of proxy change happens and when the 'Automatically Authenticate' option is enabled. I know it can't try to reconnect forever because it will cause an endless cycle for other people who have other types of proxy disconnects, but in my case it would be very helpful to let fiddler at least try once to auto reconnect (for me 1 retry is usually fine and Fiddler is able to connect to the new proxy address, but perhaps you can let the number of retries be a menu option so that users can set the number of retries that they want Fiddler to do after there was a proxy change or proxy error).


Thanks so much for your work, I really like Fiddler!

I hope you can bug fix this or add it as a feature, it will be very helpful!



Last Updated: 02 Feb 2022 14:45 by Oleg
This is a feature that's present in both the Firefox and Chrome dev tools, and it's incredibly useful. Fiddler is already great, and that would make it so much better :-)
1 2 3 4 5 6