September 27, 2017 10:00 am

Time Travel Debugging is now available in WinDbg Preview

By / Senior Program Manager, Windows Engineering Systems

We are excited to announce that Time Travel Debugging (TTD) features are now available in the latest version of WinDbg Preview. About a month ago, we released WinDbg Preview, which provides great new debugging user experiencesWe are now publicly launching a preview version of TTD for the first time and are looking forward to your feedback. 

What is TTD?

Wouldn’t it be great to go back in time and fix a problem? We can’t help you go back in time to fix poor life choices, but we can help you go back in time to fix code problems.

Time Travel Debugging (TTD) is a reverse debugging solution that allows you to record the execution of an app or process, replay it both forwards and backwards and use queries to search through the entire trace. Today’s debuggers typically allow you to start at a specific point in time and only go forward. TTD improves debugging since you can go back in time to better understand the conditions that lead up to the bug. You can also replay it multiple times to learn how best to fix the problem.

TTD is as easy as 1 – 2 – 3.

  1. Record: Record the app or process on the machine which can reproduce the bug. This creates a Trace file (.RUN extension) which has all of the information to reproduce the bug.
  2. Replay: Open the Trace file in WinDbg Preview and replay the code execution both forward and backward as many times as necessary to understand the problem.
  3. Analyze: Run queries & commands to identify common code issues and have full access to memory and locals to understand what is going on.

Getting Started

I know you are all excited and ready to start using TTD. Here are a few things you should know to get started.

  • InstallYou can use TTD by installing the WinDbg Preview (build 10.0.16365.1002 or greater) from the Store if you have Windows 10 Anniversary Update or newer at
  • Feedback: This is a preview release of TTD, so we are counting on your feedback as we continue to finish the product. We are using the Feedback Hub to help us prioritize what improvements to make. The Windows Insider website has a great overview on how to give good feedback
  • Questions: We expect you will have some questions as you work with TTD. So feel free to post them on this blog or send them in the Feedback Hub and we will do our best to answer. We’ll be posting a TTD FAQ on our blog shortly.
  • Documentation: We’ve got some initial documentation at and will be improving our content based upon customer feedback and usage. You can give us feedback or propose edits on the documentation by hitting “Comments” or “Edit” on any page.
  • Blogs: Watch for more in-depth TTD updates and tips in the future on our team’s blog

How to use TTD

You use TTD directly in the WinDbg Preview app. We have added all of the key TTD features into WinDbg Preview to provide a familiar debugging experience, which makes it intuitive to go backwards and forwards in time during your debugging session.

Record a Trace

WinDbg Preview makes it easy to record a trace. Simply click File >> Start Debugging and point to the app or process. You will have an option to Record during attach and launch. See for more information.

Replay a Trace

Once the Trace is complete, we automatically load and index the Trace for faster replay and memory lookups. Then simply use the WinDbg ribbon buttons or commands to step forwards and backwards through the code.

Basic TTD Commands

You can use the ribbon or enter the following TTD commands in WinDbg Preview. See for a complete list of TTD commands.

Final Thoughts

We are very excited to get TTD into the hands of our developers; but there are a few things to remember.

  • TTD is a preview, so we will be regularly improving performance and features
  • This only runs on Windows 10 since WinDbg Preview is a Store app
  • See documentation for TTD known issues and compatibility

Welcome to the world of time travel. Our goal is to improve the lives of developers by making debugging easier to increase product quality. Please send us feedback and feature requests in the Feedback Hub to let us know how we are doing!

Updated September 27, 2017 5:17 pm

Join the conversation

  1. Will it be possible to limit the size of the trace? I think the time travelling feature will be especially useful for debugging server code which may run very long before encountering a problem.

    • To be more specific: a ‘ring buffer’-feature would be great for the above mentioned purpose: record the last n minutes before a crash (with n being configurable).

      • These are great questions about some features that our team is considering for an upcoming release of TTD.
        For now, you cannot set the maximum size for the TTD trace file. As described in TTD help content ( the TTD trace file can quickly grow to be several gigabytes. If setting maximum file size is important to you, please send us feedback on the Feedback Hub (see how to at

        We have been testing ring buffer internally. If having a ring buffer is important to you, please send us feedback on the Feedback Hub ( to help us prioritize.

  2. Is it (or will it be) possible to record a trace on a remote machine that does not have Windows10, and then replay the trace on a Windows 10 machine? We develop enterprise software which runs on Windows 2008 R2 and Windows 2012 R2, so ideally I would like to be able to record the trace on those machines and replay them on my dev box.

    Really great to see Microsoft finally making this public. I used the old iDNA to solve countless issues when I worked at Microsoft.

    • For now, TTD recording is only supported on machines with Windows 10 Anniversary Update or greater. We are considering TTD support for down level Windows in the future. Please use Feedback Hub if down level Windows support is required for your debugging scenarios. See WinDbg blog ( for Feedback Hub instructions.
      We are excited to bring TTD to the public and look forward to hearing how it helps you solve problems faster.

  3. So, I’m attempting to try TTD, howerver, each time I attempt to launch an executable I’m getting a red bar bellow the ribbon saying : “Could not launch process under the Time Travel Debugging: The system cannot find the file specified”…

    • @Arthur, Sorry to hear about problems using TTD. Please email the WinDbg Preview log to our feedback alias Here is the easiest way to email the log data.
      • Open WinDbg Preview
      • Repro the problem you are having
      • Go to View and click the Logs ribbon item
      • Select all text in the Logs window by setting focus use CTRL + A
      • Copy using CTRL + C and Paste into email

    • It’s because the packaging seems screwed up. Go to C:\ProgramData\Microsoft\Windbg\1-1804-18003\TTD and copy TTDInject.exe to TTDInject64.exe.

      For some reason it’s looking for TTDInject64.exe instead of TTDInject.exe inside the x64 folder. This fixed the issue for me.

  4. Does it provide a web interface for playback?
    Often, we need to check the trace on the test machine which will typically not have an IDE installed. Having a web interface to upload and playback the trace helps in such cases.

  5. Related to other improvements in limiting trace file size, is there any possibility of adding a trace file “slicing” feature like in video editing? Removing any unnecessary traces before or after a breakpoint, so that only the essential traces would make it into the final “cut”(trace file) is something I could certainly use.

  6. Getting the following error when recording is started:
    Error: Trace of “C:\Temp\DI\MouseCaptureLockDemo.exe” PID:3776 did not complete successfully: status:20
    Error: Communication between the guest process and this client
    could not be established, which may be an indication of
    permissions or privileges problem.
    Error: Corrupted trace dumped to C:\temp\tdd\
    After closing this error message, I will get the following message:
    The debugging session could not be started: Empty path name is not legal

    WinDbg has been run as Admin.
    I am on a Dell PC.

    • Hi Mohamed,
      I am sorry to hear that you are getting an error trying to record your app using TTD in WinDbg Preview. It sounds like you are having problems attaching to your EXE to record. We need some additional information to help figure this out. Please send email to our external feedback alias with the following information. Optionally you can use the Windows Feedback Hub ( to provide the information.
      • What type of app are you trying to record: native, managed code, other?
      • Can you use WinDbg Preview to attach to the EXE in Temp folder without trying to record?
      • Attach a Zip file with the TTD *.err and *.out files

      Also see for help information on using TTD.