Fiddler for Linux Beta is now available for download. Try out our free web debugging proxy on Linux today and let us know what you think.

After introducing Fiddler for OS X a few months ago, we focused on delivering the same for Linux. We are strong believers in the benefits of running Fiddler on the same system that generates/accepts the traffic being watched.

Now Fiddler for Linux Beta is available for download! Get it now and hit the forum to leave your ideas and suggestions for further development.

Getting Started

Once you download the new Fiddler for Linux file, follow these steps to get up and running with it:

1. If you don’t have the Mono framework installed on your Linux machine, please download it and install it. If you already have it installed, please update it to the latest version.
2. If you just installed Mono, please open Terminal and type in:/usr/lib/mono//mozroots --import --sync
   
   NOTE: The Mono framework has its own trusted root certificates store. Currently (at mono version 4.2.4) this store remains empty after installing Mono on Linux. Fiddler uses the certificates in this store to validate the certificates of the websites visited. So you need to populate this store with a set of commonly trusted root authorities to avoid getting constant certificate warnings by Fiddler. The mozroots tool imports trusted authorities from the Mozilla LXR.
3. Extract fiddler-linux.zip to a folder you have write access to. It is recommended that the full path to the Fiddler install folder does not contain any Windows path illegal characters. (At present it is possible that some Fiddler functionality, e.g. various file exports or Fiddler Script won’t handle such paths.)
4. Open Terminal and navigate to the folder form 3.
5. Type mono Fiddler.exe in Terminal.

We decreased the time to release by basing the Jan 2017 Fiddler Release for Linux on Mono. However, this approach introduced some limitations, which we'll cover in the next section.

Limitations, Known Problems, and Workarounds

Proxy Settings

Fiddler is a proxy. So in order to see traffic in Fiddler the application generating that traffic should be set up to use Fiddler as a proxy. Fiddler tries to help you with that by changing the proxy settings on startup and reversing them back to original on quit. However, the numerous Linux distributions offer a great variety of proxy settings. Fiddler cannot support all possibilities, so we chose to support gsettings and .bashrc. If the app you are trying to debug doesn’t respect the proxy settings at these two locations, then you will have to manually point it to Fiddler. Under Linux Fiddler still runs under the default localhost:8888 address.

TLS 1.1 and 1.2 Not Supported

This is a hard limitation introduced by the current state of TLS implementation in the Mono framework. So Fiddler for Linux cannot use these protocols at present.

SSL/TLS Handshake Properties Not Available

Fiddler for Linux cannot display these at present. This is a work in progress.

Auto Update

The initial version of Fiddler for Linux can be updated only manually.

Try Fiddler for Linux Today

We're excited to release our Beta to you—try out Fiddler for Linux Beta now and be sure to head to the forums to leave us your feedback.