ILSpy is the best first dnSpy alternative for most .NET assembly inspection work, but it is not the only smart pick. dnSpy is still loved because it combined decompilation, editing, and debugging in one place, yet the original project has been archived since December 2020 [source: GitHub]. That matters if you inspect unknown binaries often, because stale tools can waste time on newer .NET builds.
TL;DR: Start with ILSpy if you need a free, clean, reliable .NET decompiler. Pick dnSpyEx if you miss dnSpy’s debugger and editing flow. For example, a small security team checking 30 internal assemblies after a failed build could use ILSpy for fast code review, then dnSpyEx for breakpoint testing in the 2 or 3 assemblies that look suspicious. Paid tools like .NET Reflector and JetBrains dotPeek are better when you want polished search, IDE links, or support.
1. ILSpy: the safe default
ILSpy is open source, free, and widely used. It handles C#, IL, metadata, resources, and project export. The interface is clean enough that a junior developer can open a DLL and understand what is going on within minutes.
It is especially good for:
- Reviewing third-party assemblies before adding them to a project.
- Checking compiler output when source code does something odd.
- Recovering logic from an old internal tool when the source is gone.
The catch is that ILSpy is mainly a decompiler, not a full debugging studio. If you need live breakpoints, memory inspection, or patching, you may hit its limits fast. Still, for read-only inspection, it is hard to beat.
2. dnSpyEx: closest to the original dnSpy feel
dnSpyEx is the obvious choice if your muscle memory still expects the old dnSpy workflow. It keeps the general feel of dnSpy and adds updates aimed at newer .NET versions. You can decompile, edit assemblies, set breakpoints, and debug managed code.
This makes it useful for malware research, plugin debugging, and legacy app fixes. Of course, use it legally. Inspect your own code, internal apps, open source projects, or files you have permission to study.
Honestly, it feels like the tool you reach for when ILSpy gives you the answer, but not the proof. You can stop execution, inspect values, and see how the app behaves at runtime.
3. JetBrains dotPeek: polished and practical
dotPeek is a free .NET decompiler from JetBrains. It feels smooth, especially if you already use Rider or ReSharper. Search is strong. Assembly browsing is tidy. Decompiled code is usually easy to read.
dotPeek can export assemblies into Visual Studio projects, which is useful when you need more than a quick glance. It also reads PDB files and supports source server data when available. That helps when debugging third-party libraries that ship symbols.
The annoying part? It can feel heavier than ILSpy for quick checks. Opening a single small DLL may take a little longer than expected. Not terrible. Just noticeable when you are repeating the same task 40 times in a day.
4. .NET Reflector: paid, mature, and still useful
.NET Reflector is one of the oldest names in .NET decompilation. It is paid software, which may be a deal breaker if you only inspect assemblies once a month. But it still has a place in teams that want a supported commercial tool.
Reflector is useful for:
- Debugging into third-party code from Visual Studio.
- Understanding APIs when documentation is thin.
- Comparing behavior across library versions.
It drives me crazy that some teams ignore paid tools on principle, then spend hours fighting rough edges in free tools. If a tool saves two engineers half a day each month, the math may work.
Image not found in postmeta5. Visual Studio decompilation: best when you are already debugging
Visual Studio is not a dnSpy clone, but its built-in decompilation support is handy. When you are debugging and step into external .NET code, Visual Studio can show generated source for code without local files. That is a big time saver.
This option is best for normal development work. You stay inside the IDE, keep your call stack, inspect locals, and avoid switching tools. It is less ideal for reverse engineering a pile of DLLs from scratch. For that, use ILSpy or dotPeek first.
How to choose the right tool
- Use ILSpy for fast, free assembly reading.
- Use dnSpyEx when you need debugging plus editing.
- Use dotPeek if you like JetBrains tools and strong search.
- Use .NET Reflector if your team wants paid support and Visual Studio integration.
- Use Visual Studio decompilation when you are already inside a debug session.
One more tip: keep at least two decompilers installed. Decompiled output can vary. If a method looks broken or messy in one tool, open it in another before blaming the assembly. That simple habit can save a lot of head scratching.
dnSpy was popular for good reason. It packed many jobs into one sharp tool. But modern .NET work is broader now. The best replacement depends on the job: quick reading, deep debugging, project recovery, or IDE-based troubleshooting. Pick the tool that fits the task, not the one with the loudest reputation.