ilspycmd

ilspycmd

.NET assembly decompiler. Converts compiled DLL/EXE back to readable C# source.

Prerequisites

dotnet tool install --global ilspycmd

Quick Reference

Task	Command
Decompile to directory	ilspycmd <assembly.dll> -o <output-dir>
Decompile single file	ilspycmd <assembly.dll> -o <output-dir> -p
Show types only	ilspycmd <assembly.dll> -l
Decompile with deps	Copy all dependency DLLs to same folder first

Common Patterns

Extract API surface from a NuGet package:

# 1. Download nupkg from NuGet.org
dotnet nuget push does not apply. Use:
# https://www.nuget.org/api/v2/package/<id>/<version>

# 2. Extract the nupkg (it's a zip)
unzip <package>.nupkg -d <dir>

# 3. Find the DLL in lib/netX.Y/

# 4. Decompile
ilspycmd <dir>/lib/net8.0/<assembly>.dll -o <output> -p

If ilspycmd fails with runtime version error:

The tool requires the exact .NET runtime it was built for. Install the missing runtime from https://dotnet.microsoft.com/download.

Limitations

• Decompiled code approximates original source. Variable names, comments, and formatting are lost.
• Obfuscated assemblies produce garbled output.
• Native AOT assemblies cannot be decompiled.

See references/decompilation-guide.md for detailed workflows.