UPX review
A free, cross-platform packer with broad format support and detailed compression controls.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
UPX is a free, portable, open-source command-line packer for compressing executable programs, DLLs, libraries, and other supported binaries. It supports Windows, macOS, and Linux, with coverage for formats including PE, ELF, Mach-O, COFF, DOS, and Atari/TOS. The tool is suited to developers, release engineers, and technical users who need to reduce binary size while retaining runtime behavior for most supported formats. It also supports multi-architecture use and perpetual licensing.
Compression control is a central strength. Users can select levels 1 through 9 or use --best, apply brute-force and multiple-method workflows, and decompress packed files with the -d option. UPX can list compressed-file information such as size and compression ratio, test compressed and uncompressed data integrity, and maintain checksums for both forms. These features make it practical when file-size reporting and verification matter alongside packing. Its command-line design favors users comfortable working with executable files and compression options rather than teams seeking a graphical workflow.
UPX is focused on compression and packing, not verified protection features. That distinction matters when the goal extends beyond reducing distribution size. The software is distributed under GPL v2+ with special permissions for compressed commercial programs, so commercial distribution requires attention to those conditions. Choose UPX for free, cross-platform executable compression with broad format coverage and adjustable workflows. Consider another option when verified protection capabilities or a less technical operating model are central requirements.
UPX pros and cons
- Where it wins
- Supports Windows, macOS, Linux, and multiple executable formats
- Offers compression levels 1–9, --best, and multiple methods
- Includes decompression, integrity checks, checksums, and size reporting
- Where it doesn't
- Command-line operation may require technical familiarity
- Provides no verified protection features
- Compressed commercial distribution has special license conditions
UPX fact sheet, pricing and score →
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