UnRAR License vs GNU GPL: Key Differences

The primary difference between the UnRAR license and the GNU General Public License (GPL) lies in software freedom and operational restrictions. While the GNU GPL is a copyleft free software license designed to grant users complete freedom to use, modify, and share software, the UnRAR license is a restrictive, proprietary "source-available" license. Although UnRAR distributes its source code publicly, it explicitly forbids developers from using that code to recreate the proprietary RAR compression algorithm, fundamentally clashing with the GPL's core principles.

Software Freedom vs. Proprietary Restrictions

The GNU GPL is maintained by the Free Software Foundation (FSF) and adheres to the Open Source Definition. It guarantees four essential freedoms: running the program for any purpose, studying how it works, redistributing copies, and distributing modified versions.

In contrast, the UnRAR license (authored by Alexander Roshal for RARLAB) is not an open-source license. It allows developers to use and distribute the UnRAR source code freely to decompress RAR archives, but it denies the freedom to use the code for general development purposes.

The Compression Restriction

The most critical legal divergence is UnRAR's explicit prohibition on developing compression tools. The UnRAR license contains a specific clause stating:

"The source code of UnRAR may not be used to develop a RAR (WinRAR) compatible compression algorithm or to reverse engineer the RAR compression algorithm without written permission."

This restriction prevents developers from studying the decompression logic to write an independent RAR encoder.

Under the GNU GPL, imposing such a restriction is strictly forbidden. Section 6 of GPLv2 and Section 10 of GPLv3 state that a distributor may not impose any further restrictions on the recipient's exercise of the granted rights. Because the UnRAR license limits what technology can be created with the code, it fails the basic criteria of free software.

Copyleft and Derivative Works

The GNU GPL is a strong copyleft license. If a developer modifies GPL-licensed code or incorporates it into a larger program, the entire derivative work must also be released under the GPL, ensuring that the source code remains accessible to end users.

The UnRAR license does not implement copyleft. Instead, it allows the UnRAR decompression code to be embedded into proprietary software, freeware, or commercial applications, provided that the UnRAR copyright notice remains intact and the restriction against building compression tools is upheld.

License Compatibility

UnRAR source code is legally incompatible with the GNU GPL. Because the UnRAR license places restrictions on usage (barring compression development) and the GPL forbids downstream restrictions, the two licenses cannot be combined into a single binary.

Due to this incompatibility, open-source operating systems and projects (such as Linux distributions) handle the software differently:

  • Purely open-source tools (like unshield or GPL-compliant archive utilities) cannot link directly against official UnRAR source code.
  • Most Linux distributions place official UnRAR packages in "non-free" or restricted software repositories.
  • GPL-compatible projects that require RAR extraction often rely on clean-room reverse-engineered alternatives, such as the unar tool or libarchive, which implement extraction without using UnRAR's restricted code.