Why UnRAR Source Code Is Freeware Not Open Source
While the source code for the UnRAR extraction utility is freely available for anyone to download, inspect, and compile, its restrictive licensing prevents it from being classified as true open-source software. Although many developers assume that accessible source code automatically equals open source, the UnRAR license contains specific prohibitions on how the code can be utilized, placing it firmly in the category of proprietary freeware or "source-available" software.
Source-Available vs. Open Source
For software to be considered "open source," it must comply with the Open Source Definition (OSD) maintained by the Open Source Initiative (OSI). The OSD requires that a license must not only allow the source code to be viewed and modified, but it must also allow derived works and must not restrict anyone from using the program in a specific field of endeavor.
UnRAR fails these standards because the copyright holder, Alexander Roshal, provides the code under a bespoke license that intentionally limits how the logic inside it can be repurposed.
The Compression Algorithm Restriction
The defining factor that makes the UnRAR source code freeware rather than open source is an explicit restriction regarding RAR compression. The UnRAR license contains a clause stating:
"The unrar utility and its source code are freeware, but you must not use the unrar source code to re-create the RAR compression algorithm, which is proprietary."
This single clause directly violates multiple criteria of the Open Source Definition:
- Restriction on Derived Works (OSD Criterion 3): Open-source licenses must permit modifications and derived works to be distributed under the same terms. By forbidding developers from using the decompression code to reverse-engineer or implement a RAR-compatible compressor, the license restricts derived works.
- Discrimination Against Fields of Endeavor (OSD Criterion 6): An open-source license cannot restrict anyone from using the code in a specific field. Barring developers from the field of RAR compression development violates this principle.
Commercial Protection for WinRAR
The reason for this restriction is business-driven. The RAR format
and its primary tool, WinRAR, are commercial products developed by
RARLAB. While RARLAB benefits from wide adoption of the format by
allowing third-party tools to decompress .rar archives,
they maintain an exclusive monopoly over the official compression
algorithm.
Allowing third-party developers to study the UnRAR source code and create full-fledged, free RAR compressors would undermine the commercial viability of WinRAR licenses.
Conclusion
Because you can obtain, compile, and distribute the UnRAR code at zero financial cost, it qualifies as freeware. However, because its license dictates what you can and cannot build with that logic, it lacks the legal freedoms required of open-source software. It remains a proprietary, source-available utility designed solely to enable file extraction while protecting the commercial interests of its creator.