I tried running some requests in Python to see if they will appear in Fiddler

For a HTTP request, it worked with no problem:

However, trying to send a request over HTTPS results in long blocking and eventually fails. Nothing is logged to Fiddler, because no actual request was made. After 20-30 seconds, a long error is raised in Python:

urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='www.google.com', port=443): Max retries exceeded with url: /?id=1234567890 (Caused by ProxyError('Your proxy appears to only use HTTP and not HTTPS, try changing your proxy URL to be HTTP. See: https://urllib3.readthedocs.io/en/1.26.x/advanced-usage.html#https-proxy-error-http-proxy', SSLError(SSLError(1, '[SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1129)'))))

What is causing Python to stop working (only while Fiddler is running)?  My current Fiddler version is v5.0.20204.45441 which is, I know, an old version. I trusted the root certificate, even installed it manually, and the HTTPS traffic from my browser is displayed normally as it should.

I've just downloaded Fiddler Everywhere for the first time and installed on my relatively virgin Mac. I am logged in as adminstrator, and have enabled capture of https, but despite visiting several unsecure and secure urls within my browser, nothing is being captured in the Live traffic capturing tab (which is enabled). 

When viewing the network proxies tab, nothing changes between when Fiddler is running and not running, both HTTP and HTTPS checkboxes are unchecked with no server details. 

Is there an additional step to configure that I am missing? 

When I use fiddler classic, response from https://ok.ru on my last laptop (Lenovo Legion Y520 Win11) is normal, but my new laptop (Asus ROG Strig G17 Win11) - have a problem with decode.

Error from Fiddler:

See the end of this message for details on invoking 
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.Exception: Brotli conversion failed
   at Fiddler.Utilities.BrotliExpand(Byte[] arrIn) in C:\Jenkins\Fiddler_Windows\workspace\FiddlerCore\FiddlerCore.Shared\Common\Core\Utilities.cs:line 2796
   at Standard.Transformer.Expand(ExpanderDelegate eD, Boolean bUpdateSizeLabel)
   at Standard.Transformer.doRaw(Boolean bUpdateSizeLabel)
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.RadioButton.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


************** Loaded Assemblies **************
mscorlib
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9093.0 built by: NET481REL1LAST_C
    CodeBase: file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/mscorlib.dll
----------------------------------------
Fiddler
    Assembly Version: 5.0.20211.51073
    Win32 Version: 5.0.20211.51073
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Fiddler.exe
----------------------------------------
System
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9093.0 built by: NET481REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System/v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Core
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9093.0 built by: NET481REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Core/v4.0_4.0.0.0__b77a5c561934e089/System.Core.dll
----------------------------------------
System.Windows.Forms
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9093.0 built by: NET481REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Windows.Forms/v4.0_4.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System.Drawing
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Drawing/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
System.Configuration
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Configuration/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
System.Xml
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Xml/v4.0_4.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
Analytics
    Assembly Version: 1.0.20182.27266
    Win32 Version: 1.0.20182.27266
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Analytics.DLL
----------------------------------------
Microsoft.GeneratedCode
    Assembly Version: 1.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Xml/v4.0_4.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
System.ComponentModel.Composition
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.ComponentModel.Composition/v4.0_4.0.0.0__b77a5c561934e089/System.ComponentModel.Composition.dll
----------------------------------------
Telerik.NetworkConnections
    Assembly Version: 0.1.2.0
    Win32 Version: 0.1.2.0
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Telerik.NetworkConnections.DLL
----------------------------------------
Telerik.NetworkConnections.Windows
    Assembly Version: 0.1.2.0
    Win32 Version: 0.1.2.0
    CodeBase: file:///C:/USERS/VALDI/APPDATA/LOCAL/PROGRAMS/FIDDLER/PLUGINS/NETWORKCONNECTIONS/TELERIK.NETWORKCONNECTIONS.WINDOWS.DLL
----------------------------------------
MetadataViewProxies_13e3577d-0d9f-40cf-b9db-c5eff2edd807
    Assembly Version: 0.0.0.0
    Win32 Version: 4.8.9037.0
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.ComponentModel.Composition/v4.0_4.0.0.0__b77a5c561934e089/System.ComponentModel.Composition.dll
----------------------------------------
Standard
    Assembly Version: 2.6.2.0
    Win32 Version: 2.6.2.0
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Inspectors/Standard.dll
----------------------------------------
SyntaxView
    Assembly Version: 2.6.2.0
    Win32 Version: 2.6.2.0
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Inspectors/SyntaxView.dll
----------------------------------------
FiddlerOrchestra.Addon
    Assembly Version: 1.0.20202.16135
    Win32 Version: 1.0.20202.16135
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Scripts/FiddlerOrchestra.Addon.dll
----------------------------------------
FiddlerOrchestra.Connection
    Assembly Version: 1.0.20202.16135
    Win32 Version: 1.0.20202.16135
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Scripts/FiddlerOrchestra.Connection.dll
----------------------------------------
netstandard
    Assembly Version: 2.0.0.0
    Win32 Version: 4.8.9037.0
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/netstandard/v4.0_2.0.0.0__cc7b13ffcd2ddd51/netstandard.dll
----------------------------------------
FiddlerOrchestra.Protocol
    Assembly Version: 1.0.20202.16135
    Win32 Version: 1.0.20202.16135
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Scripts/FiddlerOrchestra.Protocol.dll
----------------------------------------
FiddlerOrchestra.Utilities
    Assembly Version: 1.0.20202.16135
    Win32 Version: 1.0.20202.16135
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Scripts/FiddlerOrchestra.Utilities.dll
----------------------------------------
RulesTab2
    Assembly Version: 2.6.2.0
    Win32 Version: 2.6.2.0
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Scripts/RulesTab2.dll
----------------------------------------
SimpleFilter
    Assembly Version: 2.6.2.0
    Win32 Version: 2.6.2.0
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Scripts/SimpleFilter.dll
----------------------------------------
Timeline
    Assembly Version: 2.6.0.3
    Win32 Version: 2.6.0.3
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Scripts/Timeline.dll
----------------------------------------
Microsoft.JScript
    Assembly Version: 10.0.0.0
    Win32 Version: 14.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/Microsoft.JScript/v4.0_10.0.0.0__b03f5f7f11d50a3a/Microsoft.JScript.dll
----------------------------------------
System.Windows
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Windows/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Windows.dll
----------------------------------------
JScript Thunk Assembly
    Assembly Version: 0.0.0.0
    Win32 Version: 14.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/Microsoft.JScript/v4.0_10.0.0.0__b03f5f7f11d50a3a/Microsoft.JScript.dll
----------------------------------------
Accessibility
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/Accessibility/v4.0_4.0.0.0__b03f5f7f11d50a3a/Accessibility.dll
----------------------------------------
W2uBEJRg
    Assembly Version: 0.0.0.0
    Win32 Version: 14.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/Microsoft.JScript/v4.0_10.0.0.0__b03f5f7f11d50a3a/Microsoft.JScript.dll
----------------------------------------
Microsoft.GeneratedCode
    Assembly Version: 1.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Xml/v4.0_4.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
GA.Analytics.Monitor
    Assembly Version: 1.0.20182.27266
    Win32 Version: 1.0.20182.27266
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/GA.Analytics.Monitor.DLL
----------------------------------------
System.Net.Http
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Net.Http/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Net.Http.dll
----------------------------------------
System.Security
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Security/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Security.dll
----------------------------------------
Newtonsoft.Json
    Assembly Version: 11.0.0.0
    Win32 Version: 11.0.2.21924
    CodeBase: file:///C:/Users/valdi/AppData/Local/Programs/Fiddler/Newtonsoft.Json.DLL
----------------------------------------
System.Numerics
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Numerics/v4.0_4.0.0.0__b77a5c561934e089/System.Numerics.dll
----------------------------------------
System.Runtime.Serialization
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Runtime.Serialization/v4.0_4.0.0.0__b77a5c561934e089/System.Runtime.Serialization.dll
----------------------------------------
System.Data
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9093.0 built by: NET481REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_64/System.Data/v4.0_4.0.0.0__b77a5c561934e089/System.Data.dll
----------------------------------------
Microsoft.mshtml
    Assembly Version: 7.0.3300.0
    Win32 Version: 7.0.3300.0
    CodeBase: file:///C:/WINDOWS/assembly/GAC/Microsoft.mshtml/7.0.3300.0__b03f5f7f11d50a3a/Microsoft.mshtml.dll
----------------------------------------
System.Web
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.9037.0 built by: NET481REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_64/System.Web/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Web.dll
----------------------------------------

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.

For example:

<configuration>
    <system.windows.forms jitDebugging="true" />
</configuration>

When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.

Click here don`t help me 

My settings

I check test version Fiddler Everywhere, and error have here.

There's a 3rd party ios app that i want to capture traffic from, and i'm not having any luck in doing so.  It is specifically the Twinkly app.  My web requests from the browser seem to be getting decoded and i did not expect the apple apps to be decoded, due to certificate pinning, but I really would like to get this working for a 3rd party app.  I installed a bouncy castle certificate and tried that, and I also set up a trial of Fiddler Everywhere and started over, with no luck.  Any ideas?  I am willing to jump through any kind of hoop necessary to get this to work, including jailbreaking the phone.

I know that Fiddler uses local DNS resolver as it didn't work on some test sites that only worked through DoH geobypassing proxy. Are there any trick/method to make Fiddler respect browsers DoH setting? If not, would you guys please consider adding it since DoH/DoT seems to be very useful/popular these days.

Here's some use case scenarios

• You want to hide your DNS queries from your ISP while doing Fiddler session on a browser.
  
• Your ISP filters your DNS (transparent DNS proxy, etc) and you want to debug sites that are blocked by your ISP with Fiddler.
• You want to debug geo-blocked sites which can be bypassed by geo-bypassing DoH resolver.
• and so on.

You can also add following to any of the scenarios above if we think alternative solutions like using Windows 10/11, configuring DoH on the router, using VPN, etc.

• "you use an operating system that doesn't support configuring DoH/DoT"
• "your ISP/Organization blocks VPN/proxies"
• "your router doesn't support DoH/DoT"

BTW, I know Microsoft natively added DoH in Windows 10 more than a year ago, DoT to Windows 11 insider build a few months ago. I don't know if Fiddler works on them (works as in properly using DoH/DoT) as i don't use those OSes. I am curious to know about it though.

Anyways,

Here's quick guide to confirm that Fiddler/Firefox bypasses DNS-over-HTTPS just in case anyone wants to test.

Open Firefox (Use this guide for other browsers)

1. Click the menu button and select Settings.
2. In the General panel, scroll down to Network Settings and click the Settings… button
3. Check "Use system proxy settings"
   
4. Scroll down to Enable DNS over HTTPS.
5. • On: Select the Enable DNS over HTTPS checkbox.

     Check Custom and paste this server (this is DoH DNS resolver that blocks social media sites we are using for the test)
     

   • https://freedns.controld.com/p3
     

   • Press OK

6. Open www.facebook.com and it should be blocked.

7. Now open Fiddler and try to open www.facebook.com again on the browser. Facebook will work.
   

i used these settings:

public static void StartupFiddlerCore()
        {
            // Build startup settings:
            var settings = new FiddlerCoreStartupSettingsBuilder()
                                //.CaptureLocalhostTraffic()
                                .MonitorAllConnections()
                                .CaptureFTP()
                                .DecryptSSL()
                                .RegisterAsSystemProxy()
                                .OptimizeThreadPool()
                                .Build();
            FiddlerApplication.Startup(settings);
            //FiddlerApplication.oProxy.Attach();

        }

when i use WinSCP and use the fiddlerCore's ftp proxy to connect ftp server, the fiddlerCore's ftp proxy did net capture the ftp traffic.

the picture is winscp's proxy setting.

I am using fiddlerCore to capture ftp traffic, and i used the "CaptureFTP()" setting and "RegisterAsSystemProxy()" setting.

But when i use Winscp application with fiddlerCore's proxy to connect ftp server,it did not work,and connect failed. 

how dose fiddlerCore's ftp proxy work? how to use it?

Hi,

I tried

static function OnBeforeRequest(oSession: Session) {
var arr: Byte[] = oSession.requestBodyBytes;
var istr: String = '';
istr =  Convert.ToBase64String(arr);

// ... do something with request body ...

oSession.RequestHeaders['Fiddler-Encoding'] = 'base64';
oSession.utilSetRequestBody(istr);
}

base on this article. Unfortunately this does not work. Any help appreciated.

I'm using Fiddler Classic and android Emulator - MEmu. I have installed some android application there.

Of course I have installed fiddler certificates on my host and on android also i moved them to the system folder, I set up fiddler proxy in the Wi-Fi settings and everything works fine, I can receive all https traffic but somehow in this application when I'm trying to log-in the application logs in but in the fiddler I don't have any activity, it is just empty at this moment. Same thing when I enter wrong password the application says me "Wrong password" which means it sends request to the server somehow but fiddler doesn't have any requests when I press the button "Log in".

How is this possible? Can application bypass proxy that set up in the wi-fi connection settings in the android somehow? Or how is it possible even it theory?

I also tried android firewall with block all connections option on, when I Log in in the application with this firewall that blocks everything - I have error in the application and in the blocked list I can see requests like IP address and some urls, so why I can't see this requests in the fiddler?