DLL Obfuscator Online — Free .NET Library Protection

Q: Will existing callers still use my obfuscated DLL?

Class libraries preserve their public API while eligible private and internal names are rewritten. Verify assembly identity, public signatures and an unchanged consumer. Our unsigned .NET 8 example retains 24 contract entries and passes ten consumer checks; this is not a universal compatibility guarantee.

Q: Does every DLL count as a library?

No. A modern .NET application can be a DLL with a managed entry point. The entry point, rather than the extension, determines application versus library behavior. Public renaming is disabled for class libraries.

Q: Can I obfuscate a native DLL?

No. This service rewrites managed .NET assemblies. A native C/C++ DLL is not supported. Inspect the actual assembly rather than assuming the DLL extension identifies managed code.

Obfuscate a .NET DLL Free vs Pro

Public library names are a compatibility contract

A consumer compiled against InvoiceCalculator.Calculate must still resolve that type and method. For a class library, FreeObfuscator disables public renaming and targets eligible private and internal symbols instead. Compatibility exclusions may leave some implementation names unchanged.

This preserves the naming contract; it does not prove every runtime path works. Reflection, serialization, resources, signing and dependencies need application-specific checks.

Measured DLL case: compare the contract, then run the caller

We processed a self-authored .NET 8 invoice library through the production anonymous Free endpoint. The public API includes an interface, a calculator, invoice properties and an event. It is an unsigned demonstration library, not a customer SDK.

In addition to the C# calculation example, we compared the exported types, declared public members and assembly identity of the original and protected DLLs:

Check	Observed result
Exported public types	3, unchanged
Public-contract entries	24, identical; includes types, constructors, methods, properties, event and accessors
Assembly identity	InvoiceLibrary, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null; unchanged
Compiled consumer	Same consumer binary; no recompilation
Runtime comparison	10 explicit checks pass; original and protected output match
Private implementation	ILSpy shows _calculationCount → @b and RoundMoney → @d

The 24 entries are a reflection snapshot, not 24 independent behavior tests: getter/setter and event-accessor methods appear alongside their properties and event. The ten consumer checks cover five expected totals, JSON fields and round trip, events, state and an invalid-quantity exception.

Download the DLL contract case Read all 24 contract entries

The ZIP contains source, original/protected library folders, the unchanged consumer, ILSpy listings, runtime results and a contract-comparison script. Its hashes identify the captured files. A preserved signature list and one consumer do not certify every consumer, framework or publish mode.

Reproduce the DLL checks

Extract the sample and review its source and README.
Run dotnet original/InvoiceConsumer.dll, then dotnet protected/InvoiceConsumer.dll. Both assert ten checks and print the same invoice JSON.
Run the included public-API comparison script to reproduce the signature and assembly-identity comparison.
Open both InvoiceLibrary.dll files in ILSpy. Public Calculate remains, while the private field and rounding helper have short names.

For your own library, compile a consumer against the original once, replace only the library in a separate staging folder under its expected filename, and run the unchanged consumer. Recompiling the caller against the protected DLL can hide a compatibility break.

DLL extension does not mean class library

A modern .NET application may also be a DLL, with a managed entry point. That application can opt into public renaming; a class library cannot. See the application DLL and Windows launcher case for the opposite boundary. A native C/C++ DLL is not a supported managed input.

Even a private library can have other assemblies compiled against its public names. This service keeps class-library public names; requesting public renaming does not override that safeguard.

What else to test before distributing a DLL

Reflection and wire formats: exercise string-based lookups, serializers, DI conventions and resources. Explicit JSON names work in this sample; that does not cover every serializer.
Nested APIs and callbacks: verify public nested types, generic callers, interface dispatch, events and plugins actually used by your consumers.
Signing and packaging: this sample is unsigned and is not a NuGet-package validation. Independently verify strong names, package layout, assembly loading and supported target frameworks.
Release behavior: exercise normal and exceptional paths with the real dependency versions and configuration. A successful load alone is insufficient.

Frequently asked about DLL obfuscation

Will existing callers still use my obfuscated DLL?

Public class-library APIs are preserved, but test the actual callers. The measured unsigned .NET 8 sample keeps 24 contract entries and passes ten runtime checks with the same compiled consumer.

Does every DLL count as a library?

No. An application DLL can have a managed entry point. The extension is not the deciding factor, and public renaming remains disabled for class libraries.

Can I obfuscate a native DLL?

No. This tool expects a managed .NET assembly, not a native C/C++ binary.

Free supports one managed file up to 1 MB, with no account. It renames eligible symbols; strings and algorithms can remain readable. Pro adds deeper transforms and larger-file workflows. Compare the verification evidence, compatibility guide and .NET overview before choosing your settings.

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