Open & Extract 7Z Files Online — No 7-Zip Required
The 7Z format was created by Igor Pavlov as part of the open-source 7-Zip project. It's widely used for software releases, game mods, and large data archives because it achieves significantly better compression than ZIP — often 30–50% smaller for the same content. The downside: macOS, Windows, iOS, and Android don't open .7z files natively.
FastZip changes that. Drop any .7z file into the tool above and it extracts entirely inside your browser. No 7-Zip installation needed, no admin rights required, and nothing leaves your device.
LZMA2 compression — Most modern .7z files use the LZMA2 algorithm, which is optimized for multi-core processors. During extraction, LZMA2 decompresses faster than it compresses. FastZip's WebAssembly engine handles LZMA2 natively through libarchive, the same library used by most Linux distributions' archive managers.
Solid archives — 7Z supports "solid" archives where all files are compressed as a single stream. This produces the best compression ratios but means extracting a single file requires decompressing everything before it. FastZip handles solid archives correctly: it will decompress the full stream to reach your target file. For large solid archives this may take a few extra seconds.
BCJ and BCJ2 filters — 7Z archives built for executable files (software installers, game data) often use BCJ or BCJ2 pre-processing filters to further compress x86 machine code. FastZip supports these filters through its libarchive WebAssembly core.
Split 7Z archives — Files split as archive.7z.001, archive.7z.002 etc. are common for large downloads. FastZip can open the first part to show the archive listing, but combining split parts for extraction is a planned Pro feature.
Format & Feature Reference
| Feature | 7Z Format |
|---|---|
| Max archive size (free) | 200 MB |
| Compression algorithms | LZMA, LZMA2, BCJ, BCJ2, PPMd, BZip2 |
| Encryption | AES-256 |
| Filename encryption | Yes (optional) |
| Solid archive | Yes |
| File comments | No |
| Max path length | Unlimited |
| Unicode filenames | Yes (full UTF-8/16) |
Why 7Z Is Popular for Software and Game Distribution
Software developers and game modders choose 7Z because the LZMA2 algorithm consistently achieves 30–50% better compression than ZIP deflate. For a 2 GB game mod that would be 3 GB as a ZIP, the 7Z archive is often under 1.5 GB — a meaningful savings on bandwidth and storage.
Game platforms like NexusMods and software repositories like SourceForge default to 7Z for their largest downloads. If you've downloaded content from these platforms and ended up with a .7z file you can't open on your Mac or phone, FastZip is the easiest solution.
Extracting 7Z Files on macOS Without Installing Software
macOS ships with Archive Utility which handles ZIP and some TAR formats natively. It does not handle .7z. The traditional solution is to install The Unarchiver from the Mac App Store or 7-Zip from brew.
FastZip requires nothing: open fastzip.io in Safari or Chrome, drag your .7z file from Finder onto the browser window, and you'll see the file listing within seconds. Click "Extract all files" to download everything, or click individual files to download selectively. Works on Apple Silicon and Intel Macs.
How 7Z Encryption Works
7Z uses AES-256 encryption, the same standard used by banks and government agencies. When a .7z archive is password protected, not only are the file contents encrypted, but optionally the filenames as well — meaning you may not even know what's inside without entering the password first.
FastZip handles both scenarios: if filenames are visible it will show the archive listing before asking for a password; if filenames are also encrypted it will ask for the password before displaying anything. The password is processed entirely inside your browser — FastZip's servers never receive it.