Introducing Fiddler for OS X Beta 1

Fiddler for OS X Beta is now available for download. Try it out today and let us know what you think.

Over the years, we have received numerous requests from our user community to provide a Fiddler build for OS X. While Fiddler for Windows can be used as a proxy for apps running on OS X, there is still great value in being able to run Fiddler on OS X natively.

So we have ported the latest version of Fiddler to the Mono Framework which in turn supports OS X—and you can grab the beta bits today.

Download Fiddler for OS X Beta and use our Fiddler forum to leave your comments, ideas and suggestions for further development.

Getting Started with Fiddler for OS X Beta

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

1. If you don’t have the Mono framework installed on your Mac, 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:
   /Library/Frameworks/Mono.framework/Versions/<Mono Version>/bin/mozroots --import --sync 
   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 OS X. 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-mac.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.

While the Oct 2016 Fiddler Release for OS X increases development speed, this approach introduced some limitations, which you will find more details about in the next section.

Limitations, Known Problems and Workarounds

Unstable UI

Fiddler for OS X has the same familiar look that Fiddler for Windows has, however, it is built on top of the open source WinForms Mono implementation. The quality of that implementation is significantly lower than that of Microsoft WinForms, and this results in a less than ideal user experience. While we were aware of that when we began our work on the macOS version of Fiddler, we chose to go this way so that we can bring OS X support to life faster, not sacrifice the roadmap for Fiddler for Windows and base our future work on real world usage.

The most problematic areas in the UI for the beta 1 release are resizing the window and resizing elements inside the window. That oftentimes results in poor or laggy redrawing of all the affected elements. Quite often, though, hovering over or clicking on the affected areas will fix things.

When Fiddler is running and ‘decrypt HTTPS traffic’ is on, Safari cannot access some popular sites (Facebook/Twitter/GitHub etc.)

Currently this effect is limited to Safari only and it happens only if you visited the site before opening Fiddler. Cleaning the browsing history (just the history not cache or cookies) for the affected site(s) fixes the problem.

Our preliminary research shows this problem occurs with websites using TLS versions greater than 1.0. The lack of Mono implementation of TLS 1.1 and 1.2 limits Fiddler for macOS to using TLS 1.0 only. Rather unfortunately, Fiddler TLS 1.0 connection comes after TLS 1.2 connection has been made to the same domain which doesn’t seem to be acceptable to Safari.

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 OS X cannot use these protocols at present.

SSL/TLS Handshake properties not available

Fiddler for OS X Beta cannot display these at present. This is work in progress.

Auto update

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

Limited lifespan

This version of Fiddler for OS X will work for 60 days and then it will need to be updated.

Try Fiddler for OS X Today

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