A new look for .NET Reference Source

A new look for .NET Reference Source

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This post was written by Alok Shriram, Program Manager on the .NET Framework team. He will show you a significantly improved experience around .NET Reference Source.

Today I'm very excited to announce that we have an awesome new experience to use the .NET Framework reference source.

Browsing .NET Reference Source

First of all, most people just want to look at code. So we've added a brand new source browsing experience. For a tutorial, checkout our Channel 9 video:

This new browsing experience provides the following features:

  • Go to Definition and Finding References. You can now browse through .NET framework code in a Visual Studio like experience with features analogous to “Go to Definition” and “Find All References”. This tool was developed for internal use but we found it to be so incredibly useful that we had to share it with you. The video above highlights some of the cool features of this site and how you can use it. For more details, checkout the help page.

  • Offline Browsing. You can download the entire reference source as a zip file, which now also includes project and solution files, so that you can easily open and browse it in VS.

  • Jump to Reference Source right from Visual Studio. Schabse Laks has written an extension to VS called Ref12. This extension changes the behavior of F12 to jump to the online browser for symbols that aren’t in your solution but are part of the .NET Reference Source. If you have any more interesting ideas around how you can use leverage this site please touch base with us by using the feedback button on the site or leave a comment here in the post.

We generated this site using Project Roslyn, our new C# and VB compilers.

Using .NET Reference Source for debugging

We are also happy to announce that you can now step through .NET framework sources for .NET framework 4.5.1 and any associated patches and updates.

This has been one of the highest voted items on User Voice:

We are pleased to close this item as resolved. To read about how to setup VS to take advantage of this feature please go here.

So what does it mean for your day-to-day activities? Let’s assume that you have an app that uses List<string> to display a set of controls. One day after a framework update you suddenly realize that the order of the controls in your app has suddenly changed. You fire up VS and follow the instructions described above and start stepping through you code like you normally would. You get to the point where you were doing your sorting:

Hit F11 and voila you are in the List<T>.Sort code! Sweet.

We find that this is an extremely useful diagnostic tool for our developers when they are investigating issues internally. So we decided to fix this experience so that it also "just works" for you. This will give you the ability to better understand and diagnose issues between our and your code.

Improvements when debugging .NET Reference Source

Historically since the inception of this effort, we have published sources and PDBs for every major .NET framework update namely .NET framework 4.0 and 4.5. However these builds would be rendered effectively useless the moment any update to the framework was released, since the binaries on the updated box no longer matched the PDBs that were indexed on the reference source server. Unfortunately the design of the system that we had in place was geared towards doing single and infrequent pushes of sources and symbols out and did not account for the sheer volume of builds and patches that come are produced out of the .NET framework build system.

Starting with .NET 4.5.1 we have radically changed the symbol indexing and publishing process to be in sync with the build process such that as and when updates are shipped , the corresponding PDBs are also updated to the reference source site appropriately. The summary of this is going forward the reference source debugging experience should just work. If it does not use the troubleshooting instructions at the link provided above and send us an email with the data requested, we will do our best to turn it around quickly.

There is one caveat to this experiences; for security updates or updates that are otherwise deemed to have changes that we do not want leaked (think security exploits) you will still have a debugging experience, but rather than the file that corresponds to that PDB, you will get the last broadly shipped copy of that file. This could manifest itself in a slightly skewed debugging experience if you are stepping through a file where the fix was made.

How does reference source relate to the Microsoft Symbol Server?

The Microsoft Symbol Server is a repository where all public PDBs generated by most teams at Microsoft end up. However all PDBs that are present here do not have any source information in them, which makes them not very useful for stepping through sources. When you are trying to debug .NET Framework source please ensure that you do not have the Microsoft Symbol Server enabled. Doing so could result in the symbols being loaded from the Microsoft Symbol Server and the source stepping experience would not work in that case. You can disable Microsoft Symbol Server lookup via Tools | Options | Debugging | Symbols. Ensure that the checkbox in front of Microsoft Symbol Server is unchecked.

What's next?

But wait! There is more:

  • Replacing referencesource.microsoft.com. Our most immediate goal is to retire the current page at http://referencesource.microsoft.com in favor of the new browsing experience. Please take a look at the old site and let us know of any concerns you have around deprecating it.

  • Updating the indexed sources. The version of the framework that we currently have indexed is .NET Framework 4.5.1. Due to the improvements we made in our engineering system, we're now able to update both the symbols and the sources as new versions of the framework are released.

  • Adding source for assemblies. As you can probably notice, the set of assemblies that we have is not complete. We don't intend to keep it that way, so we plan to expand the set of assemblies over time.


Today we announced a new browsing experience for the .NET Reference Source. We've also fixed the long standing issue with using reference source for debugging.

We would love to hear your feedback. Please let us know what you think about the new browsing experience by leaving a comment on this blog or by emailing us. Also, if you're missing specific assemblies, please let us know so that we can prioritize which ones we add first.

Happy browsing & debugging!

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  • Please add 5 and 6 and type the answer here:
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  • 1 When can we expect to see the 4.5.2 references?

    2 I am still not able to debug into sources. I unsuccessfully tried all descriptions/hints with Win 8.1 / VS 2013 Pro / dotnet 4.5.1 installed and target / and now 4.5.2 installed and target. Never could step into list.Sort() or any other sources (except the URI Class - only in 4.5.1 !?) Pls. provide more troubleshouting with the VS settings /  Server configs.

  • Hi Alok,

    any news about wheter/when you will include DataVisualization.dll?



  • Wow! Massive effort.

  • This is awesome

  • Has anyone gotten this to work recently in VS2013? I've been trying to step into System.Configuration and have wasted hours trying to get this to work...

  • I just found an option in Reflector Pro to generate a PDB from decompiled sources. I selected System.Configuration and it worked! Thank you Reflector!

  • Has anyone got Reference Source debugging to work?   I  can't get any source code to show up.  The symbols are loaded but when I try and step into the .NET methods I get the Source Not Available page.  I've fiddle around with the symbol paths, downloaded the DotNetReferenceSource.zip, tried adding folders from that extracted Zip to my solutions's Debug Source Files property page, but still no luck.... driving me crazy!

  • Nice, although keeps crashing on System.Runtime.Serialization.Formatters.Soap

  • Help with System.Web.dll ? I can't seem to get this to show source, even trying a vanilla install on a blank vm of vs 2013 update 4. All I get is this:

    SYMSRV:  referencesource.microsoft.com/.../System.Web.pdb not found

    referencesource.microsoft.com/symbols: Symbols not found on symbol server.

    SYMSRV:  System.Web.pdb from msdl.microsoft.com/.../symbols: 131401 bytes

    msdl.microsoft.com/.../symbols: Symbols downloaded from symbol server.

    C:\Symbols\System.Web.pdb\E6EBD6B61CEA407591438CC4E48036891\System.Web.pdb: Symbols loaded.

    But no source.

    See others:



    Can't get it to work...

  • @Brandon could you reach out to us using the email on the site so that we can help diagnose/debug your issue.

    If you could provide the build number for the System.Web.dll it would be great.

  • WTF windows workflow debugging doesn't work?

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