head to head · open source
calibre vs zlib
calibre has 26,054 GitHub stars, 2,712 forks, 6 open issues and last shipped today. zlib has 524 stars, 38 forks, 1 open issues and last shipped 26 days ago. calibre leads on adoption by 4,872% (26,054 vs 524 stars). calibre is written in Python under GPL-3.0; zlib is written in Go under MIT. calibre has attracted 10% as many forks as stars, zlib 7%. calibre was the more recently maintained of the two, and both are self-hostable with no licence fee. The two share 2 topic tags (ebook, kindle), so they are genuine substitutes rather than adjacent tools.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| calibre | zlib | |
|---|---|---|
| GitHub stars | ★ 26K | ★ 524 |
| License | GPL-3.0 | MIT |
| Written in | Python | Go |
| Last push | 2026-10-03 | 2026-09-07 |
| Forks | ⑂ 2.7K | ⑂ 38 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick calibre if
- You weight community size — 26K stars and counting
- You want the GPL-3.0 license terms
- Your stack matches Python
- You value the larger contributor base for long-term maintenance
pick zlib if
- You want the zlib feature set and don't need the biggest community
- You prefer the MIT license terms
- Your stack matches Go
- You evaluated both and zlib fits your workflow better
About calibre
calibre is the official source code repository for the calibre e book manager, an open source application written in Python and released under GPL 3.0. It lives in the content and publishing ecosystem as a desktop tool for books, and it is cross platform, running on Linux, Windows and macOS. The project has been hosted on GitHub for roughly thirteen years, carries about 25,900 stars and 2,683 forks, and its home on the web is calibre ebook.com, where an About page and a screenshots page document it further.
read the full calibre overview →
About zlib
zlib is a command line interface for Z Library that lets readers search the catalogue, download ebooks, send them to a Kindle device, and drive the whole workflow from AI coding agents.
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Frequently asked questions
Is calibre or zlib more popular?
calibre has 26,054 GitHub stars and zlib has 524. calibre has the larger community by that measure.
Are calibre and zlib free?
Both are open source. calibre is licensed under GPL-3.0 and zlib under MIT. Neither carries a licence fee.
What is the difference between calibre and zlib?
calibre is written in Python and zlib in Go. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, calibre or zlib?
Choose calibre if you want the larger community (26,054 stars) or its GPL-3.0 licence terms. Choose zlib if its feature set, stack or MIT licence fits better. Both are self-hostable.