Table of Contents Acknowledgements............................................................................................................................................................ iii Table of Contents................................

Recently, a handful of folks have emailed me complaining that some HTTPS sites cannot be reached by their .NET programs or from any program when Fiddler is configured to decrypt traffic. Notably, these users only have problems when running on Windows...

With the recent kerfuffle about sites providing misleading P3P statements , I decided to throw together a quick Fiddler add-on that displays privacy information simply in the Fiddler UI. Install the new Privacy Scanner add-on and Fiddler will gain...

The new Fiddler Beta has a few useful tricks. First, you can copy a DataURI to your clipboard (from Fiddler itself, or anywhere else): and use the new Edit > Paste Files as Sessions command: … to instruct Fiddler to parse...

I’m a long-time ThinkPad fan and owner—the keyboards are sublime, and I love the TrackPoint interface. What I don’t love is the ThinkPad driver software, which doesn’t send the standard WM_MOUSEWHEEL messages to the system. That...

Back in September, I blogged about the configuration steps required to debug Windows 8 “Metro-style” apps using Fiddler . Since that post was originally written, I’ve made available a new version of Fiddler which runs natively on the...

Much work remains, but the basic architecture is in place for Fiddling with both secure and insecure HTML5 WebSockets:

Recently, a colleague asked me to look at a network capture in which a .NET client application’s communication with a web service was not meeting their performance goals. In particular, he noted that this was primarily a problem on high-latency...

For this morning’s post, I wanted to give everyone a quick picture of some of the data I've collected about Fiddler usage, how I plan to respond, and how I will continue to learn more. I’ve recently had the chance to run some surveys and...

HTML5 introduces the concept of an Application Cache, which allows a web developer to provide a manifest of pages that should be cached to permit offline use. You can see an instance of AppCache over on the IETestDrive site ; if you examine the markup...

Over on StackOverflow, a new Windows 8 user asked how to get Fiddler working with new Windows 8 Metro-style applications. These applications work somewhat differently than classic desktop applications, and require a bit of special configuration work to...

Just under a year ago, I wrote a blog post about how the new “Extended Protection” feature (also known as Channel Binding Tokens or CBT) prevented seamless decryption of certain authenticated HTTPS traffic when Fiddler is running. The quick...

This morning, someone asked me to look into a site-compatibility problem on a HTML5 demo site. When loading the site into IE9 and IE10, the F12 Developer Tools’ Script Debugger showed the following error: Now, obviously, IE does support...

I recently got a bug report from a user who was attempting to use Fiddler in a pure-IPv6 environment, where IPv4 is entirely disabled. On startup, he saw the following message: The problem here is an obscure one, which makes it somewhat interesting...

My talk at this year’s MIX conference is now complete and the video, slides, and references are now available for download. See https://www.fiddler2.com/mix/ for links. One of demos showed off a simple little extension that can be used to manipulate...

One feature added to Fiddler a few years ago is the ability to map a given HTTP request back to the local process that initiated it. It turns out that this requires a bit of interesting code, because the .NET Framework itself doesn’t expose any...

I think origin stories are fun. I spoke about the origins of Fiddler in my talk at the PDC last year, and it was interesting to share how a little idea bloomed into a surprisingly widely-used piece of software. Cleaning up some old hard drives a few weeks...

I’m delighted to announce that the now-available IE9 RC includes three significant enhancements for users of proxy-based debuggers like Fiddler. These improvements are: The default Connections-Per-Proxy limit has been raised from 6 to 12...

Back in October, I showed how to debug Windows Phone emulator traffic with Fiddler . Since then, I’ve acquired the LG Quantum phone, and naturally, one of my first goals was to start looking at the traffic from mobile Internet Explorer and...

I’ve recently heard from a number of Silverlight developers who report that certain cross-domain web service requests from their applications work properly with Fiddler running, but fail when Fiddler is not active. Using lower-level tools like NetMon...

Note: Please see this post for an update. Some users of Fiddler who have HTTPS Decryption enabled have found that some of their internal HTTPS sites that used to work properly with Fiddler now endlessly prompt for credentials while Fiddler is running...

Note: This post is part of a larger set on using Fiddler with Windows Phone 7 . This post covers the Windows Phone Emulator only. Recently, some developers have asked me why Fiddler no longer works with the Windows Phone 7 emulator. Fiddler properly...

FiddlerCore version 2.3.0.4 is now available for download. The primary change in this update is that the installation package now includes FiddlerCore4.dll, a version of the assembly compiled to run on the .NET4.0 CLR. I expect to maintain versions of...

The Request Builder feature in recent versions of Fiddler includes a number of enhancements, including the ability to follow HTTP redirections, and to automatically authenticate (using the current user's credentials) to servers that demand authentication...

New features and fixes in the Beta . The Find Sessions feature (CTRL+F) now supports searching with regular expressions. Enhanced the "Compare Sessions" feature on the context menu (set fiddler.differ.ultradiff = "False" if you don't like it...