ilspy-decompile

Decompile a compiled assembly when you need the real implementation - a framework internal, a NuGet package you have no source for, or the exact behavior of a method before you upgrade across it. For source you already have, navigate with serena / the LSP instead; this is only for compiled .dll you cannot open otherwise.

Tool

ilspycmd, via either form (pick whichever the environment has):

dnx ilspycmd -h                       # needs the .NET 10 SDK
dotnet tool install --global ilspycmd # or pin per-repo in .config/dotnet-tools.json

Flags vary by version - confirm with ilspycmd -h.

Locate the assembly