dnSpy

dnSpy is a free, open-source .NET debugger, decompiler, and assembly editor. It brings together a decompiler, an integrated code editor, and debugging tools to inspect, modify, and run .NET assemblies. Users can open executables and libraries, view and decompile code into C# or IL, and edit the decompiled source. Changes can be rebuilt and saved back to disk, enabling patching or in-place updates of assemblies. The tool also includes a metadata and type browser, a resource viewer, a hex editor, and an IL-to-C# converter, making it useful for reverse engineering, diagnostics, and understanding compiled .NET code.

dnSpy supports debugging managed code, including breakpoints, inspection of variables, and step-through execution. It can attach to running processes or launch applications under the debugger, and it supports symbol loading to improve the accuracy of decompiled output and debugging information.

Platform and licensing: dnSpy runs on Windows as a .NET desktop application (built with WPF) and is distributed under an open-source license, specifically the GNU General Public License version 3.0.

History and reception: The project originated in the mid-2010s as an open-source alternative to proprietary .NET decompilers. Development has experienced periods of varying activity, with community-driven forks and continued releases by volunteers sustaining its availability. It is widely used by developers for learning, analysis, and interoperability tasks, while users should ensure compliance with software licenses and applicable laws.