WinZST

WinZST is a Windows archive utility derived from 7-Zip. It focuses on making tar archives and compressed tar archives behave like normal Windows archives.

The core idea is simple:

compressed tarball in -> final contents out

When a user extracts example.tgz, example.txz, example.tbz, example.tar.zst, or example.tzs, the expected output is the archive contents, not an intermediate .tar file.

WinZST is tarball-first, not Zstandard-only. Zstandard-compressed tarballs are the preferred default, but WinZST also supports other tar workflows such as gzip, bzip2, XZ/LZMA2, GNU tar, and POSIX tar, while keeping broad archive support inherited from 7-Zip.

Why WinZST Exists

Compressed tarballs are common, portable, and useful, but Windows archive tools often expose their internal layering in awkward ways.

A user who downloads this:

project.tar.gz

usually wants this:

project/

not this:

project.tar

WinZST exists to make tarballs worth downloading on Windows.

Archive Formats

WinZST keeps the inherited general archive utility model, but gives tar formats better first-class treatment.

Primary creation formats include:

Format	Typical extension	Notes
WinZST archive	.tzs	Standard tar archive compressed with Zstandard
Tarball with Zstandard	.tar.zst	Expanded form of .tzs
Tarball with gzip	.tgz, .tar.gz	Common Unix/Linux tarball format
Tarball with bzip2	.tbz, .tbz2, .tar.bz2	Older but still common compressed tar format
Tarball with XZ/LZMA2	.txz, .tar.xz	High-compression tarball format
GNU tar	.tar	Plain tar archive using GNU tar behavior where supported
POSIX tar	.tar	Plain tar archive using POSIX tar behavior where supported
ZIP archive	.zip	Standard Windows-compatible archive format
7-Zip archive	.7z	Inherited compatibility format

Other inherited archive formats may remain supported where licensing, maintenance, and security allow.

The .tzs Format

.tzs is WinZST's preferred archive extension.

.tzs == .tar.zst

A .tzs file is a standard tar archive compressed with Zstandard.

It is not:

• a proprietary container
• a renamed .7z archive
• a renamed .zip archive
• a WinZST-only format
• encrypted by default

A .tzs archive should remain compatible with standard tar plus Zstandard tooling. In practice, this means a user should be able to rename:

archive.tzs

to:

archive.tar.zst

and extract it with tools that understand tar and Zstandard.

The purpose of .tzs is Windows usability: a short, recognizable extension for a standard tar plus Zstandard archive.

Tarball Extraction Behavior

WinZST should extract compressed tarballs directly to their final contents.

For example, if this archive:

example.tgz

contains:

example/
example/file.txt

then normal extraction should produce:

example/
example/file.txt

It should not produce:

example.tar

This behavior applies to supported compressed tarball formats, including:

.tzs
.tar.zst
.tgz
.tar.gz
.tbz
.tbz2
.tar.bz2
.txz
.tar.xz

The tar layer is an implementation detail during normal extraction.

Decompress-Only Behavior

WinZST may support decompress-only behavior for advanced users.

For example:

example.tgz -> example.tar
example.txz -> example.tar
example.tzs -> example.tar

That is valid when the user explicitly asks for the raw tar stream.

However, decompress-only is not the default behavior. Normal archive extraction should give the user the final files and folders.

Project Status

WinZST is an early fork of the 7-Zip source tree.

The first target platform is:

Windows 11 x64

Early builds may be experimental and unsigned. Windows SmartScreen or similar trust prompts should be expected until release signing is established.

The current .tzs and .tar.zst creation path writes a tar archive through the bundled libzstd streaming encoder. It is standard tar plus real Zstandard compression, not stored/raw placeholder blocks, a renamed .7z, a renamed .zip, or a WinZST-only wrapper. Re-run tests/test-zstd-archive-creation.ps1 after compression changes to verify creation, listing, testing, extraction, hash matching, size ratios, and tar plus Zstandard compatibility.

Relationship to 7-Zip

WinZST is derived from 7-Zip.

That inheritance is important. The existing 7-Zip codebase provides mature archive parsing, extraction, compression, Windows GUI infrastructure, shell integration, build rules, and broad format support.

WinZST is not official 7-Zip and is not endorsed by upstream 7-Zip.

WinZST must preserve applicable upstream copyright notices, LGPL notices, third-party notices, and unRAR license restrictions.

RAR Support

WinZST may keep inherited RAR extraction support where the source tree and licenses allow it.

RAR support is extraction-only.

WinZST does not create .rar archives and must not use unRAR-derived code to recreate the proprietary RAR compression algorithm.

Building

WinZST uses the inherited upstream 7-Zip NMAKE build system.

The PowerShell helper scripts in build-helpers/ wrap that build flow from the repository root. They do not replace the upstream build system.

Requirements:

• Windows
• PowerShell
• Visual Studio 2022 Build Tools
• MSVC C++ toolchain
• Windows SDK

Default build:

.\build-helpers\build.ps1

Clean rebuild:

.\build-helpers\build.ps1 -CleanFirst

Build File Manager:

.\build-helpers\build.ps1 -Target Fm

Clean helper-supported targets:

.\build-helpers\clean.ps1 -Target All

If PowerShell blocks the helper scripts because they are unsigned, run them with an explicit temporary execution policy bypass:

powershell -ExecutionPolicy Bypass -File .\build-helpers\build.ps1

or:

powershell -ExecutionPolicy Bypass -File .\build-helpers\clean.ps1 -Target All

Testing Expectations

A build is not useful just because it compiles.

At minimum, WinZST should be tested for:

• opening archives
• listing archive contents
• creating .tzs
• creating .tgz
• creating .tbz
• creating .txz
• creating plain .tar
• extracting .tzs directly to contents
• extracting .tar.zst directly to contents
• extracting .tgz and .tar.gz directly to contents
• extracting .tbz, .tbz2, and .tar.bz2 directly to contents
• extracting .txz and .tar.xz directly to contents
• keeping .zip extraction and creation working
• keeping .7z extraction and creation working
• testing archives without extraction
• preserving safe extraction behavior

A WinZST build that creates .tzs but breaks ZIP or 7z is not good enough.

A WinZST build that still extracts compressed tarballs to intermediate .tar files by default is not good enough.

Security Notes

Archive extraction handles untrusted input and writes to the filesystem.

WinZST must preserve safe extraction behavior and should prefer Windows-safe tar extraction over perfect Unix metadata restoration.

Do not weaken checks for:

• path traversal
• absolute paths
• drive-qualified Windows paths
• UNC paths
• unsafe symlinks
• unsafe hardlinks
• alternate data streams
• unsafe overwrites
• password handling
• plugin loading
• archive parser behavior

Tar metadata is not harmless. Symlinks, hardlinks, device files, owners, groups, permissions, and unusual paths all need careful handling on Windows.

Safety beats compatibility.

Non-Goals

WinZST is not trying to be:

• a new proprietary archive format
• a replacement compression algorithm
• a cloud storage product
• an Electron rewrite
• a Rust rewrite
• a cosmetic 7-Zip reskin
• a RAR creator
• a fork that hides its upstream origin

The goal is narrower and more practical:

Make tarballs behave correctly on Windows.

License

WinZST is derived from 7-Zip and retains the applicable upstream license structure.

The source tree includes LGPL-covered code, third-party code under other compatible terms, and unRAR-derived code with additional restrictions.

Do not remove license files or upstream notices.

See the included license documents for details.