Visual disassembler for .NET assemblies
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spec structs.txt

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Have you ever wondered what was inside your C# EXE or DLL? Have you ever tried to modify a binary and got some weird CLR exception? dotNetBytes can help.

There are many good .NET disassemblers out there, and there are many good visual explanations of what the pieces of a .NET assembly are. I wanted the best of both worlds, having a tool to create a custom visualization of my assemblies.


  • See a structured view of the PE file header, CLI metadata, and the byte-code
    • look in the Table of Contents on the left
  • See the raw hex codes and ASCII view of the bytes
    • bytes are colored based on grouping and ToC selection
  • Understand little endian numbers, bit flags, and string blobs
    • look though the detail view on the right
  • Errors are listed in red details
  • Relative and absolute addresses are hyperlinked
    • look for the cursor to change

Try It!

Try it out at


I was working on a C# assembler and I was frustrated when running the EXE failed with useless errors. Without this app, you might need to resort to reading through the EMCA-335 spec to find the off-by-one error in your metadata tables or op codes.


There are many ways to help out!

  • You can try out the app at the website or try cloning it yourself.
  • You can file issues for any problems or questions you run into.
  • You can file issues with any suggestions or features requests you have.
  • You can submit pull requests for any issues or to add testing.

Software design

There's two main parts to the app, a C# back-end and a JavaScript frontend.

There are four major parts:

  • dotNetBytes has the disassembly library, and a command line host to serve static files
  • dotNetBytes/view is the web frontend
  • WebHost is a ASP.NET server, hosting the disassembly library.
  • Test is a bunch of test cases of different C# and IL features. Please make sure they all pass before you submit a PR.

When coding on the frontend, I normally:

The interface is the frontend POSTS the assembly, and the back-end returns recursive JSON description of the entire assembly, in this recursive format:

    "Name": "SomeUniqueName"
  , "Description": "Notes about this node based on the language spec"
  , "Value": "A ToString() view of the node\n Can Be multiple lines"
  , "Start": StartingByteIndex
  , "End": EndingByteIndex
  , "LinkPath": Path/To/Another/Node
  , "Errors": ["Any problems in the bytes that violate the language spec"]
  , "Children": [ { $DescriptionsOfTheInnerNodes }, ... ]

Scenarios for full test pass

  • From http-server, open
  • From VS run dotNetBytes, look at "YAML" command line output, click around
  • From VS run WebHost, Open root URL, upload EXE, modify EXE, Try Example
  • Run Tests unit project