ZIP to TAR.GZ
Nothing you choose here leaves your browser, and nothing is downloaded to make it work — not a library, not a compression module, nothing. Your browser already knows how to deflate and gzip; this page writes the tar.gz around it.
The usual reason: something on a Unix machine wants a tar.gz.
The files are unpacked here and repacked as a tar, then gzipped. The result is normally within a few per cent of the ZIP, because both end up using deflate — gzip compresses the whole tar in one go rather than each file separately, so an archive of many small similar files often comes out slightly smaller.
How this works, and why nothing is fetched
Your browser already knows how to deflate and gzip, because it needs both to load web pages. This page reaches that through CompressionStream and DecompressionStream and writes the archive structure itself — a ZIP directory or a tar header, both of which are byte layouts rather than algorithms. Nothing is fetched and nothing is installed.
What it will not do
It will not open a RAR, and nothing ever writes one: RARLAB's licence forbids using their code to re-create the RAR algorithm, which is proprietary. That is a legal restriction and not a difficulty. It will not open a 7z, bzip2 or xz either — those need compressors your browser does not have, so supporting them would mean shipping one, which is the thing this page avoids. It says which of these it is looking at rather than just refusing.
It does not open password-protected archives, and it says so per file rather than failing silently. It reads plain ZIPs rather than ZIP64, so an archive over 4 GB or with more than 65,535 files is refused with that reason given.
Where to go next
- TAR.GZ to ZIP — the same conversion the other way
- ZIP to TAR — uncompressed, and it keeps Unix permissions
- JSON to CSV — for the data inside them