Add !dns [hostname] and !nslookup [hostname] to list DNS info to Log tab
Add !listen PORT [CERTHOSTNAME] to QuickExec
Add audio/video/font/silverlight/flash/HTTP-POST Session icons
Revamp a few toolbar icons
Enable +/- latency adjustments using AutoResponder
Add fiddler.ui.inspectors.request.alwaysuse and fiddler.ui.inspectors.response.alwaysuse preferences
Changed "Remove Un-Marked" to ignore breakpointed sessions
Added fiddler.ui.CtrlX.KeepMarked and fiddler.ui.CtrlX.PromptIfMoreThan # (to replace CONFIG.iPromptBeforeClearAll)
Add Screenshot toolbar command, including delay option
Delay-Create FiddlerScript file behind pref "fiddler.script.delaycreate", defaults to true
Add IE10 User-Agent to default rules
Add AlwaysFresh option to Performance menu
Add fiddler.requestbuilder.followredirects.max preference
Add actInvertSelectedSessions() with hotkey of CTRL+I
about:network is now a synonym for about:connectoids
Add support for SELECT @REQUEST.HEADER VALUE, use * to test for existence or "\*" to match on a literal star.
Various bugfixes

Version 2.3.3.0 - Released 4/12/11

Improved AutoResponder with latency and per-rule editor
Add support for QuickLinkMenu and QuickLinkItem
Various bugfixes

Version 2.3.2.7 - Released 4/3/11

Allow save/load of session content to FARX file, using compression if needed
Added "Open URL" to AutoResponder rules menu
Add "11" to Options > Font Size dropdown; enable CTRL+Plus, CTRL+Minus, CTRL+0
Set the mouse cursor for the interactable panels on the Status Bar
Support sequential requests via # token in RequestBuilder
Don't trim a User-Marked/Commented session
Add "Remove Un-Marked" to toolbar menu
Update _replaceVirtualHostnames to update request line for CONNECT tunnels
Fixed the directly-specified Proxy script handling code; added fiddler.network.gateway.DetermineInProcess preference
Fix AutoResponder's Connect+AlternateURL scenario
AutoResponder now emits detailed 404 error if session has a process ID or was generated by Fiddler
Update installer for Win7+ You must use "Turn Windows features on or off" in the Control Panel to install or configure Microsoft .NET Framework 2.0 SP2 for Windows 7+

Version 2.3.2.3 - Released 2/12/11

 Improved Performance
Improved AutoResponder
Improved support for Windows Phone emulator
Edit preferences with about:config
Various small improvements
Lots of bugfixes

Version 2.3.0.5 - Released 10/1/10

Various small improvements
Lots of bugfixes

Version 2.3.0.0 - Released 7/23/10

Various small improvements
Lots of bugfixes

Version 2.2.9.6 - Released 6/24/10

Import/Export feature
Tons of bugfixes

Version 2.2.8.6 - Released 1/28/10

Added -viewer switch for new "view only" mode
Improved Filters tab
Improved Request Builder
Improved FiddlerHook for Firefox
Various bugfixes

Version 2.2.7.5 - Released 11/9/09

64-bit support
Added Tools > HOSTS
Improved inspectors
Improved performance
Various bugfixes

Version 2.2.4.2 - Released 8/4/09

Improved Text Encoder/Decoder
Improved performance
Improved FiddlerHook
Various bugfixes

Version 2.2.2.0 - Released 4/18/09

New Fiddler toolbar
Improved Timeline
Performance and fidelity improvements
Include WebView inspector by default
Various bugfixes

Version 2.2.1.4 - Released 3/31/09

Added FiddlerHook Firefox Extension
Hook all connections by default
Improved TextWizard
Improved default behavior of Find dialog
Allow drag/drop of files to AutoResponder to create new rules
Assorted bugfixes

Version 2.2.0.7 - Released 12/17/08

Assorted bugfixes

Version 2.2.0.5 - Released 12/1/08

"Monitor all connections" option
Support for commenting on sessions
Enhanced QuickExec
Added "Decode compressed content" option to Find Sessions
UI columns now extensible via BindUIColumn or AddBoundColumn APIs
Unlocking of sessions (see context menu) for editing after completion
Assorted bugfixes

Version 2.2.0.0 - Released 11/11/08

Improved Autoresponder
Improved user-agent spoofing
Improved performance
Support for BZip2 compression

Version 2.1.9.2 - Released 9/16/08

Lightweight process filter in status bar
New "quiet mode" feature (-quiet on command line)
Improved request builder
Various bugfixes

Version 2.1.8.2 - Released 8/5/08

Improved AutoResponder, including playback from .SAZ file
Support http://ipv4.fiddler and http://ipv6.fiddler
Added > < and = operators to QuickExec
Improved HTTPS Certificate Error handling
Filter rules automatically reload
Minor performance improvements
Various bugfixes

Version 2.1.6.2 - Released 5/3/08

Improved Fiddler Options dialog
ProcessID column added to Session List
Process Filter added to Filters tab
Improved Upstream Gateway support
Improved Performance
AutoStream Video option
Various bugfixes

Version 2.1.4.4 - Released 3/10/08.

Improved HTTPS support
Improved installer compatibility with Vista
Fixed Win2k bug preventing use of Fiddler

Version 2.1.4.2 - Released 3/1/08.

Improved Inspectors and Extensions
Map requests back to process ID (oSession.oFlags["x-ProcessInfo"])
Added Response Templates
Improved AutoResponder (RegEx support)
Various bugfixes

Version 2.1.3.6 - Released 1/28/08.

SmartScroll of Session List
Enhanced Timers
Many bugfixes

Version 2.1.2.0 - Released 11/12/07.

Improved APIs for automation
Improved inspectors
Improved SimpleFilter tab
Improved HTTP compression efficiency
Improved international support
Improved TextWizard
Many bugfixes

Version 2.1.1.1 - Released 9/15/07.

New context menu Select Parent/Children/Duplicates (or hit D,C,P)
SimpleFilters tab now included by default
Improved Session Archive File format with timestamps
Improved streaming mode
Improved inspectors
Improved performance
Improved extensibility
Improved international support
Improved search box
Improved Header editor including header templates
Many bugfixes

Version 2.1.0.4 - Released 7/6/07.

General Improvements
Introduced Client certificate support
Improved performance
Numerous bugfixes

Extensibility Improvements
Added FiddlerApplication.UI
Added CodeDescriptions to Fiddler.CONFIG, updated visibility of some functions

Version 2.1.0.2 - Released 6/28/07.

Extensibility Improvements
Added IFiddlerExtension, IAutoTamper, and IHandleExecAction interfaces
List loaded Fiddler Extensions in Options dialog
Added FiddlerApplication object
Added oSession["log-drop-request-body"] and oSession["log-drop-response-body"]
Added bBufferResponse to Session object
Added UriScheme property to HTTPRequestHeaders & Parse it from request headers
See http://www.fiddler2.com/fiddler/dev/IFiddlerExtension.asp

Improved HTTPS/Networking Support
New IPv6 options
Defaulted HTTPS-decryption to false
Added "Learn more" link for HTTPS support
Reloading secure traffic correctly reloads protocol
Added "Enable IPv6" to Tools > Fiddler Options
Added CaptureFTP Registry value and CONFIG.bCaptureFTP
Added CLR Version and Windows Version to Exception Reporting

Version 2.0.9.0 - Released 5/25/07.

Improved Inspectors (WebForms/Cookies/Hex/Etc)
Improved Save As WebTest
Support for HTTPS connection reuse and upstream HTTPS gateways
More explicit http errors on malformed response.
Various bugfixes

Version 2.0.8.8 - Released 4/12/07.

Improved WebTest Export code
Improved "Caching" inspector
Introduced /noattach command-line option
Added Session.ResetSessionCounter();
Rudimentary Session.Timer introduced
Added WinINETCache information to session Properties dialog

Version 2.0.8.7 - Released 3/11/07.

Fixed Image inspector to size correctly
Improved AutoFiddler support
Introduced SAZ file extension for ZipArchives
Fixed race condition in root certificate generation
Improved IPv6 support

Version 2.0.8.5 - Released 2/14/07.

Fixed "Simulate modem speeds"  feature (request-trickle-delay, response-trickle-delay) for HTTPS traffic

Version 2.0.8.4 - Released 2/13/07.

Version 2.0.8.3 - Released 1/29/07.

Completed AutoResponder tab
Minor new features, bugfixes.

Version 2.0.8.1 - Released 1/16/07.

Version 2.0.8 - Released 11/25/06.

First public alpha

Version 2.0.7 - Released 11/10/06.

Version 2.0.4- Released 8/23/06.

Version 2.0.3 - Released 8/20/06.

Fixed hang when notifying of new version
Smooth scrolling of Session List
Tools | Fiddler Option to disable HTTPS decryption
Assorted bug fixes; code forked from Fiddler v1.2.0.7

Version 2.0.2 - Released 8/17/06.

Exception handling no longer crashes process
Fixed up CertMaker to set correct EKU
Added IgnoreServerCertErrors option
Disabled Server Cert revocation check

Version 2.0.1 - Released 8/16/06.

Updated release with significant improvements to stability.
Harmless (in Fiddler 1.2) exceptions now result in process termination if you acknowledge the Watson dialog (Apparently, an improvement in .NET 2.0. Later builds use a workaround).

Save the following as C:\program files\fiddler\fiddler.exe.config
<configuration>
<runtime>
<legacyUnhandledExceptionPolicy enabled="1" />
</runtime>
</configuration>

Version 2.0 - Released 8/9/06.

Initial Release

Fiddler v1.x Changelog

Click here to see latest Beta change log.

Note: Fiddler v1.x has been retired; all future updates will only be made for Fiddler v2, above.

Version 1.3.0.0 - Released 6/1/07.

Many bugfixes
Updated SampleRules.js
Improved Inspectors; WebForms, Hex were major rewrites
Improved performance-timers
Added Timer calculations to Performance Statistics tab
Added Password-protected archive option; Click the "Save As Type" dropdown on the Save Dialog

Version 1.2.2.5 - Released 4/13/07.

Improved inspectors & AutoResponder
Changed ZipArchive to use .SAZ file extension
Introduced AutoFiddler extensibility interface
Performance improvements
Many bugfixes and improved error messages

Version 1.2.2.0 - Released 1/30/07.

New AutoResponder features simplify tampering
Many new rules; added Performance submenu to Rules menu
Improved QuickExec box below session list (type HELP)
Improved Inspectors; added IAutoFiddle support
Improved Reporter tab with chart improvements
Improved TextEncoder
Improved options dialog
More flexible Request builder
Improved Visual Studio WebTest export
Improved RFC2616 support
Performance improvements
Many bugfixes and improved error messages

Version 1.2.0.7 - Released 8/20/06.

Many bug fixes
Added InfoTip if response is encoded
Added Authentication Inspector
Session Properties view shows # bytes downloaded (helpful when downloading huge files through Fiddler. Hit F5 to refresh)

Version 1.2.0 - Released 6/29/06.

Fixes to support Windows Vista
Improved support for Rules Menu items
New version check feature
Header inspector enables editing all headers at once
Significant performance improvements

Version 1.1.9 - Released 5/18/06.

Added QuickExec box (Hit Alt+Q)
IPv6 Literal Support
Support for request chunking
Performance Report improvements
Web-Test Export Bugfixes
ImageViewer improvements (e.g. Middle+Click to dump image to desktop)
Added FontSize to Options dialog
Added lightweight Request Form viewer
Added HideOnMinimize option
Created ExecFiddlerAction.exe for use by command line tools wishing to drive Fiddler
Added actResumeAllSessions()
Added "GetTokenValue" to HTTPHeaders object
Dozens of miscellaneous bugfixes

Version 1.1.6 - Released 3/1/06.

Introduced support for upstream proxy autodetection and configuration scripts (http/https delivered scripts only)
Enhanced Find Sessions feature with new options
Added "Clone response" to session context menu
Fixed upstream NTLM/Negotiate proxy support
When DebugSpew is on, both requests and responses dumped to debug console in hex format
Change default for CaptureCONNECT to True
Added FiddlerObject.UI.actReloadInspectors() added to simplify inspector development
Fixed Save as WebTest in various ways
Allow userscript to override the hostname used to determine upstream IP, without changing the HTTP headers. This enables HOSTS-file type scenarios where a request should be sent to an alternative server.  e.g. in your OnBeforeRequest() handler, put code like: if (oSession.host=="production.example.com") { oSession["x-overrideHost"] = "development.example.com" }  Obviously, this doesn't work if you have an upstream proxy, and you have to just tweak oSession.host directly for those cases.
Performance and Robustness improvements

Version 1.1.0 - Released 11/29/05.

Critical security update
New View | Stacked Layout option
Autobreakpoints now ignore images by default
Image inspector offers two scaling modes
Insert key marks current session
Prompts to install WinDiff if Session Compare can't find it
String registry entry "CompareTool" enables custom Compare tool choice
Autobypass upstream proxy for hostnames "127.0.0.1" and "localhost" (only downside is can't chain instances)
.NET Framework v2.0 now detected by installer

Version 1.0.5 - Released 11/15/05.

Rebuilt proxy registration code to ensure Fiddler leaves settings as it found them
Hex inspector again installs as it now works on Windows Vista beta2.
Slight tweaks to default session colors
Changed file-save dialogs for clarity
Script can set state to SessionStates.Done to abort further processing
Improved NTLM handling (It's now believed to be bug free!)
Updated Session Archive feature
Changed default for Server socket reuse to ON
Updated Find Sessions form to automatically cycle color choices
Fiddler Options dialog is now sizable
Added View Bytes option to Text Decoder applet
Fiddler now supports autohooking connection other than the default LAN connection
Fixed race condition in server socket pool

Version 1.0.1 - Released 8/30/05.

Fiddler will only load public, non-abstract types as Inspectors
UI-tweak: Double-click in status bar panels to enable/disable capturing or set automatic breakpointing
Added Load Sessions option on File menu
Added new flags request-trickle-delay and response-trickle-delay
Fixed Windows Vista installation issue. Note Hex Inspector does not run on Windows Vista.
Fixed startup code to show running instance if possible
New icons for 204/401/403/5xx/HEAD
New color choices for Find results
Prefaced all Fiddler-generated HTTP Response status lines with "Fiddler -"
Added Spoof IE6 to default rules
Updated so NTLM doesn't show "0" for second part of handshake.
Added support for TextEditor registry key respected by the "View in Notepad" button on Standard::TextView
Fixed JSEditor persistence on option screen
Fixed duplicate accelerator on Options dialog

Version 1.0.0 - Released 7/7/05.

Restructured menus for clarity
Improved support for Windows Vista
Improved SSL CONNECT capture
Minor bugfixes

Version 0.9.9 - Released 2/1/05.

Fix to Chunked Transformer
Minor bugfixes

Version 0.9.8 - Released 12/29/04.

New scripting methods improve power
Scripting rules now stored in My Documents\Fiddler\Scripts
Header inspector improvements
Breakpoint experience cleanup
Improved Menu Extensibility via script
Assorted robustness improvements and bug fixes

Version 0.9.6 - Released 8/31/04.

Edit | Find now implemented
Scripting methods renamed for clarity; now stored in CustomRules.js
Text Encoder/Decoder no longer limited to one instance
Header Inspector now allows editing of >256 byte entries
Header Inspector now breaks out cookies for easier reading
CTRL+ALT+F systemwide hotkey
Menu Extensibility via script (see included script for examples)
Better UTF8 support in XML Inspector
Assorted bug fixes

Version 0.9.5 - Released 6/24/04.

Copy Headers now works much better (no more junk like <!-- StartFragment-->)
Dramatically improved NTLM rules handling (aka: rules now run)
Header Inspector now allows editing
Supports OnBoot, OnShutdown, OnAttach, OnDetach in EventHandlers.js
New x-fiddler-markitalic and x-fiddler-markstrikeout attributes for Session.Flags
Assorted performance improvements
Assorted bug fixes

Version 0.9.4 - Released 5/28/04.

Assorted bug fixes
New "Copy | Full Summary" feature to capture Sessions List data
Reorganized menus

Version 0.8.6 - Released 1/21/04.

JScript.NET auto-tampering rules and filters
Single-step debugging
Basic hand tampering now supported using TextView inspector only
Reorganized menus

Version 0.8.3 - Released 1/2/04.

Added SSL Tunneling
Added Chunked-Encoding
Added some basic spoofing options
Lowered memory consumption / increased speed
Reorganized menus

Version 0.8.2 - Released 10/26/03.

Added NTLM / Negotiate support
Fixed crash when an existing proxy erroneously prepended HTTP:// in IE Proxy Settings
HTTP Method / Response line more prominently displayed
Incremental Find Feature in TextView inspector
Download time approximations added to Statistics
Improved boot performance
Reorganized menus

Version 0.8 - Released 10/6/03.

Initial Release, supporting most viewing tasks