dnSpy

Editing exe and dll files

dnSpy is a highly powerful and open-source tool specifically designed for software developers and security researchers, enabling reverse engineering within the .NET ecosystem (C#, VB.NET, F#).

Simply put: If you have a program that only has an executable file (.exe or .dll) and no source code, dnSpy allows you to look inside that file, read its code, and even modify it.

Here are the key features and uses of dnSpy:
1. Decompiler

When a .NET file is compiled, it's not converted into machine language, but into an intermediate language called "IL". dnSpy converts this complex IL code back into readable C# code. This allows you to see how a program runs in the background, what algorithms it uses, or what data it processes.
2. Debugger

dnSpy is more than just a viewer. It can stop a running program, traverse it line by line (step-by-step), and examine the current values ​​of variables. Most impressively, it allows you to debug any .NET application as if it were your own code, even without the source code.
3. Assembly Editing (Code Modification)

When you find an error in the program's code or want to change a feature, you can right-click and select "Edit Method" to edit the code in C#. dnSpy will recompile the changes you made within seconds, allowing you to update the original file.
4. User-Friendly Interface

It has an interface very similar to Visual Studio, which allows developers to use it without feeling unfamiliar. It offers themes (like dark mode), multi-tab support, and advanced search features.
In what situations is it used?

    Lost Source Code: If your company has an outdated application and the source code is lost, you can recover it with dnSpy.

    Security Analysis: Used to determine whether a software program is performing malicious actions or where it is sending data.

    Modding and Patching: Modding closed-source games or tools is often done to fix minor bugs.

    Learning: You can examine the code of a professional library or application to understand how it delivers a feature.

In summary

dnSpy is like the "Swiss Army Knife" of the .NET world. It's a technological marvel that unlocks the inside of closed-box software, making it transparent and giving you complete control. As stated on the project's GitHub page, although development has ceased (it's archived), it remains one of the most stable and popular tools in the industry.