How to zip to 7z (browser) vs command-line tar / gzip / 7z
- Step 1Decide whether you truly need native 7Z — If a downstream system requires a
.7zextension or LZMA2 specifically, the browser tool cannot help — use a real7zinstall. If you just need 'smaller, and openable in 7-Zip', the browser TAR.GZ output is fine. - Step 2For the browser path: convert in a tab — Open zip-to-7z, drop one
.zip, download the.tar.gz. No flags, no options — it always uses GZIP level 6. This is the no-install path. - Step 3For the gzip-equivalent CLI path — On a machine with
tar: extract the ZIP (unzip in.zip -d out/), thentar czf out.tar.gz -C out .. This produces the same kind of output as the browser tool, with control over the gzip level viaGZIP=-9 tar czf .... - Step 4For the maximum-compression CLI path — Install p7zip / 7-Zip and run
7z a -mx9 out.7z out/after extracting. This produces a true.7zwith LZMA2, typically 5–15% smaller than the TAR.GZ on text — the gap the browser tool cannot close. - Step 5Compare the sizes that matter to you — If the size delta is small (binary-heavy archive), the browser tool's convenience usually wins. If it is large (big text/source tree) and you ship it often, the
7zratio may justify the install. - Step 6Pick by context, not dogma — Use the browser tool for one-off, ad-hoc, privacy-sensitive conversions where install is friction. Use the CLI for scripted, repeated, ratio-critical pipelines. They are complementary, not rivals.
Browser ZIP to 7Z tool vs CLI approaches
Feature matrix. The browser tool's row reflects its real behaviour (TAR.GZ output, GZIP level 6, no options, tier-capped). CLI rows assume a standard install.
| Aspect | JAD ZIP to 7Z (browser) | tar czf / gzip (CLI) | 7z a -mx9 (CLI) |
|---|---|---|---|
| Output container | .tar.gz (TAR + GZIP) | .tar.gz (TAR + GZIP) | .7z (native LZMA2) |
| Compression algorithm | DEFLATE (GZIP) level 6 | DEFLATE, level configurable | LZMA2, level configurable |
| Install required | None — runs in browser | Usually pre-installed on Linux/macOS | Must install p7zip / 7-Zip |
| Upload / network | None — fully local in tab | None — local | None — local |
| Typical size on text | Baseline (GZIP) | Same as browser (GZIP) | ~5–15% smaller (LZMA2) |
| Compression options | None (fixed level 6) | Full (-1..-9) | Full (-mx1..-mx9, dictionary, etc.) |
| Size ceiling | Tier: 50 MB Free … 2 GB Developer | Disk-bound | Disk-bound |
| Encrypted ZIP input | Not supported (no password field) | Needs unzip -P first | Needs decrypt first |
Rough compression-ratio expectations
Indicative only — actual ratios depend heavily on content. The browser tool and tar czf use the same DEFLATE family, so they land together; 7z (LZMA2) pulls ahead most on highly-redundant text.
| Content type | Browser TAR.GZ | tar czf (gzip -6) | 7z -mx9 |
|---|---|---|---|
| Source code / text | Baseline | ~same as browser | 5–15% smaller than TAR.GZ |
| Logs / CSV (very redundant) | Good | ~same | Often noticeably smaller |
| Binaries / executables | Modest | ~same | 3–8% smaller than TAR.GZ |
| Already-compressed (JPEG/MP4/ZIP) | ~no gain | ~no gain | ~no gain |
Cookbook
Real decision scenarios. Each shows the command-line equivalent next to the browser tool so you can see exactly what you trade.
Reproduce the browser tool on the command line
The browser tool is effectively 'extract ZIP, tar it, gzip level 6'. Here is the exact CLI equivalent — same output container, same algorithm family.
Browser: drop in.zip on zip-to-7z -> download in.tar.gz (gzip level 6) CLI: unzip in.zip -d in_extracted/ tar czf in.tar.gz -C in_extracted . Result: both are TAR.GZ; sizes within rounding of each other.
When 7z is genuinely worth the install
A 200 MB source-tree archive shipped weekly. The 7z LZMA2 ratio saves real bandwidth over time, justifying the install and the script.
Browser TAR.GZ: 58 MB 7z -mx9: 49 MB (~15% smaller) Weekly ship x52 = ~470 MB/yr saved -> install 7z, automate it. Command: 7z a -mx9 weekly.7z src/
When the browser tool wins outright
One-off conversion on a managed work laptop with no admin rights and a sensitive archive. No install possible, no upload allowed — the browser tool is the only zero-friction option.
Constraints: no admin (can't install 7z), no upload (sensitive data) CLI 7z: blocked (can't install) Upload tool: blocked (data can't leave device) Browser zip-to-7z: works -> local, no install -> in.tar.gz
Binary-heavy archive: the ratio gap nearly vanishes
For an archive of already-compressed media, 7z's LZMA2 advantage shrinks to almost nothing, so the browser tool's convenience wins.
Archive of 50 JPEGs + 3 MP4s (300 MB): Browser TAR.GZ: 298 MB 7z -mx9: 297 MB (<1% better) Verdict: not worth installing 7z — use the browser tool.
Encrypted ZIP: neither browser nor 7z reads it directly
Both the browser tool and a 7z re-compress need the data decrypted first. The browser tool has no password field, and 7z compresses, it does not silently decrypt a foreign-encrypted ZIP either — you extract first.
in.zip is AES-encrypted.
Browser zip-to-7z: fails (no password field).
CLI: 7z x in.zip -pSECRET -oout/ # decrypt+extract
7z a out.7z out/ # then compress
For the browser path, extract with multi-format-extractor first.Edge cases and what actually happens
Assuming the browser output is a real .7z
Mislabel riskThe tool is named for the search term but outputs .tar.gz. If a downstream process literally checks for a .7z magic header or extension, it will fail. The browser metrics state 'Native 7Z: unavailable in browser' — read them before assuming.
Expecting 7z-level compression from the browser tool
Won't happenThe browser tool uses GZIP/DEFLATE level 6, not LZMA2. On compressible text the gap to 7z -mx9 is usually 5–15%. If that margin matters for your payload size, you need a native 7z install — no browser tool here closes it.
CLI tar on Windows behaving differently
Platform quirkWindows tar (bsdtar) and Git Bash tar differ slightly in flag handling from GNU tar. If you script the CLI equivalent across OSes, pin the gzip level explicitly and avoid relying on environment defaults. The browser tool sidesteps this entirely (always level 6).
7z installed but not on PATH
Setup gapA common CLI pitfall: 7-Zip is installed but 7z is not on PATH, so scripts fail with 'command not found'. The browser tool has no PATH/install dependency, which is part of why it is preferred for ad-hoc use.
Tier cap vs disk capacity
Capacity differenceThe browser tool refuses archives over the tier cap (50 MB Free, up to 2 GB Developer). CLI tools are bounded only by disk. For very large archives, the CLI is the practical choice; for normal sizes, the cap is rarely hit.
Reproducible output across tools
DiffersGZIP streams embed a timestamp and the OS byte, so byte-identical output across gzip, the browser tool, and runs is not guaranteed even for identical contents. If you need reproducible archives, normalise inputs first; do not diff the compressed bytes — diff the extracted contents.
Empty directories handled differently
Differstar can preserve empty directories; the browser tool drops ZIP directory entries during extraction, so empty folders vanish from its output. If empty folders are semantically meaningful, use the CLI or add a placeholder file.
Timestamps: browser uses 'now', tar preserves
Differstar preserves original file mtimes by default; the browser tool stamps every entry with the current time. For builds that depend on timestamps, this matters — normalise with timestamp-normalizer or prefer the CLI.
Frequently asked questions
Does the browser ZIP to 7Z tool produce a real .7z?
No. It produces .tar.gz. Real 7Z (LZMA2) writing in a browser needs a heavy WASM encoder the tool does not ship, so it re-packages as TAR.GZ. The metrics explicitly say 'Native 7Z: unavailable in browser'. The output still opens in 7-Zip because 7-Zip reads TAR.GZ.
Is the browser tool's compression as good as 7z?
No — it uses GZIP/DEFLATE level 6, comparable to tar czf, not LZMA2. Expect a 5–15% larger file than 7z -mx9 on compressible text, 3–8% on binaries, and roughly no difference on already-compressed media. For maximum compression you need a native 7z install.
When should I use the browser tool over the CLI?
When you cannot or do not want to install software, when the archive cannot be uploaded (the browser tool keeps it local), for one-off conversions, and when 'opens in 7-Zip and is reasonably small' is good enough. The CLI wins for scripted, repeated, or ratio-critical pipelines.
What is the exact CLI equivalent of this tool?
Extract the ZIP, then tar czf out.tar.gz -C extracted .. That reproduces the browser tool's output (TAR + GZIP). The browser tool fixes the gzip level at 6; on the CLI you can override it with GZIP=-9 or gzip -9.
Does the browser tool upload my archive anywhere?
No. The conversion runs entirely in your browser tab with fflate — the archive never leaves your device. In that respect it matches a local CLI for privacy, but with zero install.
Can I control the compression level in the browser?
No — it is fixed at GZIP level 6 with no options. To experiment with levels on a ZIP, use compression-level-optimizer; to choose a different target container, use archive-format-converter.
Which is faster, the browser tool or 7z?
For normal-size archives the browser tool is effectively instant and beats the round trip of opening a terminal. For very large archives, native code may finish a high-compression pass faster than a single-threaded browser pass — but 7z -mx9 is also slower by design. It depends on size and level.
Are file contents identical after conversion?
Yes for the browser tool and for tar/gzip — both are byte-lossless on contents; only the container changes. 7z is also lossless on contents. Verify any of them with checksum-generator on the extracted files.
What about encrypted ZIPs?
Neither the browser tool nor a 7z re-compress reads encrypted ZIP data directly — you must decrypt first. The browser tool has no password field; extract with multi-format-extractor first, then convert the plaintext.
Will the output be reproducible byte-for-byte?
Not guaranteed. GZIP embeds a timestamp/OS field, and the browser tool stamps entries with the current time, so compressed bytes can differ between runs even for identical contents. Compare extracted contents, not compressed bytes, when checking equivalence.
Does the browser tool keep empty folders like tar does?
No. It drops ZIP directory entries during extraction, so empty folders disappear. tar can keep them. If empty folders matter, use the CLI or add a .gitkeep-style placeholder file before zipping.
Is there a tool that converts the other direction (TAR.GZ to ZIP)?
Yes — see tar-gz-to-zip. For arbitrary conversions among ZIP, TAR.GZ, and GZIP, use archive-format-converter.
Privacy first
Every JAD Archive tool runs entirely in your browser using fflate, @zip.js/zip.js, and the libarchive WASM bridge. Your archives never leave your device — verified by zero outbound network requests during processing.