ILSpy

ILSpy is a free, open-source .NET assembly browser and decompiler. It enables users to inspect compiled assemblies (DLLs and EXEs) and reconstruct high-level source code from the Common Intermediate Language (CIL) used by the .NET framework. The project is designed as a practical, open alternative to proprietary decompilers, serving developers, security researchers, and learners.

Key features include a graphical user interface for browsing assemblies, decompiling code to C# and Visual Basic .NET, viewing IL code and metadata, and inspecting embedded resources. ILSpy also offers a search function, the ability to export decompiled code, and a decompiler backend that can be extended. In addition to the GUI, the project provides a command-line tool (ilspycmd) for automation and scripting, as well as a library that allows embedding decompilation functionality into other applications. The software supports plug-ins and localization to aid integration and accessibility.

Development and licensing are driven by a community of volunteers. ILSpy is hosted on a public repository where contributors add features, fix bugs, and respond to issues. As an open-source project, it aims to remain free for use in code analysis, debugging, and education. While primarily a Windows desktop application, its underlying libraries and tooling are usable in broader .NET contexts and can be integrated or extended in other environments.

ILSpy has become a widely used tool in the .NET ecosystem as a transparent, accessible method for examining compiled assemblies, complementing other reverse-engineering and debugging workflows.

---