OSI-licensed open source
A software license key generator creates signed keys or license files that your application can verify, so you can enforce trials, seats or feature flags. Open-source options are mostly libraries rather than hosted services, and you build activation and billing around them.
This page lists six maintained libraries in C++, .NET, Java and Go. We excluded hosted or self-hosted licensing servers whose licences are not OSI open source, such as Keygen (Fair Core License) and LicenseGate (Elastic License 2.0). Remember that client-side licensing can always be bypassed by a determined user.
Tools, licences and pricing checked against vendor and repository pages on November 7, 2026.
| Tool | Best for | Pricing | Licence |
|---|---|---|---|
| licensecc | C++ desktop apps | Free, open source | BSD-3-Clause |
| Standard.Licensing | Modern .NET apps | Free, open source | MIT |
| Portable.Licensing | Cross-platform .NET | Free, open source | MIT |
| TrueLicense | Java apps | Free, open source | Apache-2.0 |
| License3j | Java license files | Free, open source | Apache-2.0 |
| lk | Go applications | Free, open source | MIT |
Best for: C++ desktop apps · Free, open source
licensecc provides software licensing and copy protection in C++, with few dependencies and cross-platform support.
Best for: Modern .NET apps · Free, open source
Standard.Licensing is an easy-to-use licensing library for .NET Framework, Mono, .NET Core and MAUI products.
Best for: Cross-platform .NET · Free, open source
Portable.Licensing is a cross-platform licensing framework for creating and validating licenses.
Best for: Java apps · Free, open source
TrueLicense is an open-source engine for licence management on the Java Virtual Machine.
Best for: Java license files · Free, open source
License3j is a free Java library for managing license files.
Best for: Go applications · Free, open source
lk is a simple licensing library for Go.
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| If you need… | Start with |
|---|---|
| C++ desktop software | licensecc |
| Modern .NET | Standard.Licensing, Portable.Licensing |
| Java | TrueLicense, License3j |
| Go | lk |
Quick answers to common questions
Keygen's repository uses the Fair Core License, which is not OSI open source.
Yes; client-side checks can be bypassed, so pair them with server validation.
These are libraries; you build activation and billing yourself.
Its repository uses the Elastic License 2.0, which is source-available rather than OSI open source.
List it on TechLogHub and we'll review it for this guide.
