Fiddler Web Debugger

Fiddler is a web debugging tool which is owned, developed, and distributed by Eric Lawrence.

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  • Blog Post: Visual Studio 2012, IIS Express, and Fiddler

    From the mail bag... Q: When I use IE10 on Windows 8 to visit an IIS Express instance using the following URL http://ipv4.fiddler:2468/, I get an unexpected error message. HTTP/1.1 400 Bad Request Content-Type: text/html; charset=us-ascii Server: Microsoft-HTTPAPI/2.0 Date: Wed, 22 Aug 2012 19...
  • Blog Post: My book “Debugging with Fiddler”, is now available

    I’m delighted to announce that my new full-length book on Fiddler is now available. Weighing in at 330 pages, it covers every feature in Fiddler, and provides the most comprehensive available documentation of how to develop Fiddler extensions (including Inspectors, Transcoders, and IFiddlerExtensions...
  • Blog Post: Sneak Peek at Table of Contents for the Upcoming Fiddler Book

    Table of Contents Acknowledgements............................................................................................................................................................ iii Table of Contents..................................................................................
  • Blog Post: Cookie Scanning with Fiddler

    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 a new top-level menu named Privacy. The...
  • Blog Post: ThinkPad Scrolling and Fiddler

    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 bug means that many .NET controls don’t scroll...
  • Blog Post: Revisiting Fiddler and Win8+ Immersive applications

    Back in September, I blogged about the configuration steps required to debug Windows 8 Immersive (“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 .NETv4 Framework, enabling Windows 8...
  • Blog Post: Glimpse of the future: Fiddler and HTML5 WebSockets

    Much work remains, but the basic architecture is in place for Fiddling with both secure and insecure HTML5 WebSockets:
  • Blog Post: .NET HttpWebRequests and Expect: 100-continue

    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 networks; each of the dozens of requests took hundreds...
  • Blog Post: News on Fiddler Surveys and Telemetry

    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 spend some time with developers who are using Fiddler...
  • Blog Post: Generating HTML5 AppCache Manifests with Fiddler

    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, you can find that the HTML tag contains a manifest...
  • Blog Post: Fiddler and Windows 8 Metro-style applications

    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 get Fiddler to work properly. Fear not, however...
  • Blog Post: Swapping out JQuery with Fiddler

    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 getElementsByTagName, and I confirmed that the...
  • Blog Post: Fiddler and IPv6-only environments

    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. What’s happening is that Fiddler...
  • Blog Post: MIX2011 Fiddler talk is now live

    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 GeoLocation web service responses, allowing...
  • Blog Post: Fiddler and the IE9 Release Candidate

    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, improving performance and in some cases reducing...
  • Blog Post: Fiddler and the Windows Phone 7 Emulator

    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 captured traffic from the CTP version of the emulator...
  • Blog Post: Automatic Authentication with the Request Builder

    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 using the NTLM or Negotiate (NTLM/Negotiate) challenge...
  • Blog Post: New Features in Fiddler 2.2.9.9 Beta

    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) Use a preference to persist the Scaling Mode preference...
  • Blog Post: New Features in FiddlerCore 2.2.9.9

    Version 2.2.9.9 of the FiddlerCore .NET class library has been released . This new version includes a number of new features that make FiddlerCore more useful for a variety of traffic monitoring and capture scenarios. With the exception of the final improvement (Server Read Callback), all of these improvements...
  • Blog Post: The Fiddler Community

    With a development team of one, Fiddler is in many ways a product of the rich community and ecosystem that has developed over the last six years. While I try to keep the official site updated, there are many other outlets to take advantage of when looking for Fiddler-related news, help, and tools. ...
  • Blog Post: Peeking at Fiddler’s Internals

    Fiddler 2.2.9 includes two new features that allow you to get some more insight into the state of the web debugger. The first allows you to inspect the caches used by Fiddler; simply type about:cache in the QuickExec box and Fiddler will display the current contents of its DNS Resolver cache and ServerPipe...
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