DLL Decompiler Online

For Windows app distributions, use the MSIX package viewer or APPX extractor to inspect bundles, manifests and supported managed assemblies.

What is a DLL File?

DLL stands for Dynamic Link Library. It is a file format used on Windows for shared libraries — code modules that can be loaded and used by multiple programs at the same time. DLLs allow code reuse and modular application architecture.

In the .NET ecosystem, DLLs are the primary way to distribute class libraries, frameworks, and reusable components. Many NuGet packages distribute managed DLLs; others contain native libraries, content or dependency metadata.

.NET DLL vs Native DLL

There are two fundamentally different types of DLL files:

• .NET DLL — contains CIL (Common Intermediate Language) bytecode with rich type metadata. Can be decompiled back to readable C# or VB.NET source code. Examples: Entity Framework, Newtonsoft.Json, ASP.NET libraries. This tool handles these files.
• Native DLL — contains compiled machine code (x86/x64). Found in Windows system directories (kernel32.dll, user32.dll) and C/C++ applications. Cannot be decompiled to high-level source code, but is still inspected here; see below.

How .NET DLL Decompilation Works

.NET DLLs contain CIL bytecode along with extensive metadata: type definitions, method signatures, field declarations, custom attributes, and assembly references. This metadata is far richer than what native code retains, which is why .NET decompilation produces much better results.

The decompiler reads the PE (Portable Executable) headers, parses the .NET metadata tables, and reconstructs high-level C# source code from the CIL bytecode. The output includes proper type inference, reconstructed LINQ expressions, async/await patterns, and other modern C# features.

What You Get From a Native DLL

A DLL with no CLR directory is native code, and the .NET decompiler is skipped rather than run and left to report that there is no managed metadata. The file is read structurally instead, which for a native library is often exactly what the question was:

• info/exports.txt — every exported function with its ordinal, and any forwarders to other libraries. This is the DLL's public interface.
• info/imports.txt — what the library itself depends on, delay-loaded imports included
• info/pe.json — architecture, subsystem, section table and data directories
• info/version.txt and resources/ — the version block, the manifest as XML, icons rebuilt into openable .ico files, and every other resource with its id and language

This is metadata and resource extraction, not source recovery, and the result labels it that way. An Authenticode certificate table is reported as present or absent only — nothing is hashed and no chain is built, so it is not a signature check. Reading native machine code itself is a job for a disassembler such as Ghidra or IDA.

Standard UPX-packed libraries are expanded to a separate copy first, confirmed by running UPX rather than by trusting UPX0 section names, and the expanded copy is classified again — so a .NET assembly hidden under the packing still reaches the C# decompiler. Your uploaded file is never modified and nothing is executed.

Common Uses for DLL Decompilation

• Inspecting third-party libraries — understand how a library works internally when documentation is insufficient
• Debugging without source — investigate exceptions or unexpected behavior in compiled libraries
• NuGet package analysis — review the source code of NuGet packages before adding them to your project
• Legacy code recovery — recover source code from old DLLs when the original source has been lost
• Security auditing — analyze DLLs for vulnerabilities, hardcoded credentials, or suspicious behavior

Frequently Asked Questions