Troubleshoot Fiddler Everywhere Not Capturing Traffic

Troubleshooting Fiddler Everywhere Not Capturing Traffic

If Fiddler Everywhere is running but not capturing HTTP(S) traffic, even when:

  • The application is launched and running.
  • The Fiddler root CA (certificate authority) is correctly installed.
  • The chosen capturing mode is enabled.
  • No active filters or rules are blocking traffic.

And you see the message:
"It looks like you are unable to capture traffic. You might have a configuration issue - check our troubleshooting page for more information.",

This article provides troubleshooting steps and solutions to help you identify and resolve common issues that may prevent Fiddler Everywhere from capturing traffic.

Common Causes and Solutions

Below are the most frequent reasons Fiddler Everywhere may not act as a system proxy, along with troubleshooting steps and solutions:

Lack of Administrative Rights

Fiddler Everywhere requires administrative rights to set and unset the operating system proxy settings.

Troubleshooting:

  1. Start Fiddler Everywhere as an administrator.
  2. Enable system capturing mode.
  3. Open your OS proxy settings and check if Fiddler sets the manual proxy (default: 127.0.0.1:8866).

If Fiddler cannot set/unset the proxy, it likely lacks the necessary rights.

Solution:
Reinstall Fiddler Everywhere with administrative rights or consult your system administrator.

Incompatibility with VPN Tools

Some VPNs modify network settings, which can interfere with Fiddler's proxy.

Troubleshooting:

  1. Test Fiddler Everywhere with your VPN disconnected.
  2. Test again with the VPN connected.

If Fiddler only works when the VPN is off, the VPN is likely causing the issue.

Solutions:

  • Bypass VPN Servers:
    Add your VPN server addresses to Settings > Connections > Bypass Fiddler for URLs that start with and save.

  • Use Alternative Capturing Modes:
    Try browser capturing mode or terminal capturing mode instead of system capturing.

Incompatibility with Security Tools

Security tools or policies may block Fiddler's proxy configuration.

Troubleshooting:

  • Audit your security tools and policies for restrictions on:

Solutions:

  • Ask your administrator to:

    • Allow Fiddler Everywhere to run with admin rights.
    • Permit proxy configuration.
    • Open the default proxy port (8866).
    • Ensure system requirements are met.

  • Use Alternative Capturing Modes:
    Try browser capturing mode or terminal capturing mode.

Incompatibility with Other Preset System Proxies

Complex proxy setups (e.g., PAC scripts) may prevent Fiddler from chaining to the upstream proxy.

Troubleshooting:

  • Test if Fiddler works after removing the upstream proxy from OS settings.

Solutions:

  • Configure the upstream proxy to allow Fiddler's proxy (127.0.0.1:8866).
  • Adjust PAC scripts or proxy settings as needed.

  • Consult your network administrator.

  • Use Alternative Capturing Modes:
    Try browser capturing mode or terminal capturing mode.

Incompatibility with Third-Party Proxy Tools

Some proxy tools overwrite Fiddler's proxy settings instead of chaining to them.

Troubleshooting:

  1. Start Fiddler Everywhere and enable system capturing.
  2. Confirm traffic is captured.
  3. Start the third-party proxy tool and enable its capturing mode.

If Fiddler stops capturing, the third-party tool is likely overwriting the proxy settings.

Solutions:

  • Start the third-party proxy tool before enabling Fiddler's system capture.
  • Stop the third-party proxy tool before starting Fiddler.
  • Configure the third-party tool to chain to Fiddler's proxy (127.0.0.1:8866).
  • Check the tool's documentation for chaining options.
  • Use Alternative Capturing Modes:
    Try browser capturing mode or terminal capturing mode.

Limited Internet Connectivity

Fiddler Everywhere requires access to certain endpoints for authentication and cloud features:

https://*.telerik.com/
https://*.getfiddler.com/
https://fiddler-backend-production.s3-accelerate.amazonaws.com

If these endpoints are blocked, you may see login errors.

Solutions:

  • Use a network that allows access to these endpoints.
  • [Enterprise only] Use Fiddler's offline mode (Windows only; contact support for details).

Incompatibility with Graphics Drivers

Fiddler may fail to start or display a white screen due to incompatible graphics drivers.

Solutions:

  • Update your graphics drivers from the official source.
  • Disable hardware acceleration by adding "disableHardwareAcceleration": true to %userprofile%\.fiddler\Settings\electron-settings.json.
    Learn more...

Receiving AutoProxy Detection Failed Error

If your system uses the ProxySettingsPerUser group policy set to 0, Fiddler needs admin rights to set the proxy for all users.

Solutions:

  • Run Fiddler Everywhere as administrator.
  • Change the registry entry value to 1 or remove ProxySettingsPerUser.
    Learn more...

Receiving ERR_CONNECTION_RESET Error

If you see ERR_CONNECTION_RESET only when using Fiddler, it often means the Fiddler CA certificate is not installed correctly.

Solution:

  1. In Fiddler Everywhere, go to Settings > HTTPS > Advanced Settings.
  2. Click Reset CA.
  3. Restart your client application and try again.

If the issue persists:

  1. Remove all Fiddler CA certificates from your OS certificate manager.
  2. Reinstall the CA via Settings > HTTPS > Trust CA Certificate in the User Store or via Settings > HTTPS > Trust CA Certificate in the Machine Store.
  3. Enable the HTTPS capturing via Settings > HTTPS > Capture HTTPS Traffic option.

This error may also appear in browser capturing mode. In that case, manually remove all Fiddler CA certificates and reinstall.

Other Scenarios

If you still cannot resolve your issue:

Testing macOS Network Access

macOS-specific configurations may prevent Fiddler from detecting the active network adapter. See this KB article for troubleshooting.

See Also

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