dnSpy is a debugger and .NET assembly editor. You can use it to edit and debug assemblies even if you don't have any source code available.
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The following pictures show dnSpy in action. It shows dnSpy editing and debugging a .NET EXE file, not source code.
- Debug .NET Framework, .NET Core and Unity game assemblies, no source code required
- Edit assemblies in C# or Visual Basic or IL, and edit all metadata
- Light and dark themes
- Extensible, write your own extensions
- High DPI support (per-monitor DPI-aware)
- And much more, see below
dnSpy uses the ILSpy decompiler engine and the Roslyn (C# / Visual Basic) compiler and many other open source libraries, see below for more info.
Latest build: 
Or build it from source, see the Wiki.
- Debug .NET Framework, .NET Core and Unity game assemblies, no source code required
- Set breakpoints and step into any assembly
- Locals, watch, autos windows
- Variables windows support saving variables (eg. decrypted byte arrays) to disk or view them in the hex editor (memory window)
- Object IDs
- Multiple processes can be debugged at the same time
- Break on module load
- Tracepoints and conditional breakpoints
- Export/import breakpoints and tracepoints
- Call stack, threads, modules, processes windows
- Break on thrown exceptions (1st chance)
- Variables windows support evaluating C# / Visual Basic expressions
- Dynamic modules can be debugged (but not dynamic methods due to CLR limitations)
- Output window logs various debugging events, and it shows timestamps by default :)
- Assemblies that decrypt themselves at runtime can be debugged, dnSpy will use the in-memory image. You can also force dnSpy to always use in-memory images instead of disk files.
- Public API, you can write an extension or use the C# Interactive window to control the debugger
- All metadata can be edited
- Edit methods and classes in C# or Visual Basic with IntelliSense, no source code required
- Add new methods, classes or members in C# or Visual Basic
- IL editor for low-level IL method body editing
- Low-level metadata tables can be edited. This uses the hex editor internally.
- Click on an address in the decompiled code to go to its IL code in the hex editor
- The reverse of the above, press F12 in an IL body in the hex editor to go to the decompiled code or other high-level representation of the bits. It's great to find out which statement a patch modified.
- Highlights .NET metadata structures and PE structures
- Tooltips show more info about the selected .NET metadata / PE field
- Go to position, file, RVA
- Go to .NET metadata token, method body, #Blob / #Strings / #US heap offset or #GUID heap index
- Follow references (Ctrl+F12)
- BAML decompiler
- Blue, light and dark themes (and a dark high contrast theme)
- Bookmarks
- C# Interactive window can be used to script dnSpy
- Search assemblies for classes, methods, strings, etc
- Analyze class and method usage, find callers, etc
- Multiple tabs and tab groups
- References are highlighted, use Tab / Shift+Tab to move to the next reference
- Go to the entry point and module initializer commands
- Go to metadata token or metadata row commands
- Code tooltips (C# and Visual Basic)
- Export to project
- ILSpy decompiler engine (C# and Visual Basic decompilers)
- Roslyn (C# and Visual Basic compilers)
- dnlib (.NET metadata reader/writer which can also read obfuscated assemblies)
- VS MEF (Faster MEF equals faster startup)
- ClrMD (Access to lower level debugging info not provided by the CorDebug API)
- Iced (x86/x64 disassembler)
Click here if you want to help with translating dnSpy to your native language.
See the Wiki for build instructions and other documentation.
dnSpy is licensed under GPLv3.