Looking for a Calibre alternative?
Usually that search means you keep a serious library in Calibre and mostly need the library part: find a book, fix its metadata, move on. Calibre is remarkable software that can do almost anything to an ebook, and that power adds up to a lot of interface for those everyday sessions.
Citadel is a free, MIT-licensed desktop ebook library manager for macOS (Apple Silicon) and Linux, built for exactly those sessions. It is not a Calibre clone and doesn't try to match it feature for feature. It replaces the part you look at all day: the library window.
It's also, deliberately, not a server. Most Calibre alternatives (Calibre-Web, Kavita, Komga) are self-hosted web apps you administer and visit in a browser. Citadel is desktop software like Calibre itself: it opens the library on your disk, works offline, and needs no setup.
The part that makes it low-risk
Citadel works on your existing Calibre library, in place: the same folder layout, the same metadata.db, the same on-disk format. There is no import step and no export step. If Citadel isn't for you, delete it and open Calibre; nothing moved. The project's compatibility bar is that Calibre must always be able to read a library Citadel has edited. Anything less is treated as a bug.
Where Citadel replaces Calibre
- Browsing and filtering a library, responsive into the thousands of books
- Editing metadata (title, authors, tags, identifiers, languages) with lookups from the Library of Congress, Open Library, Deutsche Nationalbibliothek, and K10plus
- Importing EPUB, MOBI, and CBZ files into the library
- Opening books in your default reading app
- Keeping each book's metadata.opf in sync with your edits
Where it doesn't (yet, or on purpose)
- Format conversion: Calibre's home turf, and out of scope by design
- Reading and editing ebooks: Citadel opens your reader instead
- Device management and sync: not yet
- Content server, news fetching, plugins: no plans
- Windows builds: not published yet
If you rely on any of those, keep Calibre installed. Using Citadel for the day-to-day library window doesn't require giving anything up, because both apps read the same library.
At a glance
| Citadel | Calibre | |
|---|---|---|
| Scope | Library management, focused | Everything ebooks |
| Library format | The same Calibre library on disk, fully shared | |
| Interface | Native desktop app, light and dark | Qt app, dense and endlessly configurable |
| Format conversion | No | Yes, best in class |
| Built-in reader | No; opens your default app | Yes |
| Device sync | Not yet | Yes |
| Plugins | No | Yes |
| Platforms | macOS (Apple Silicon), Linux | macOS, Windows, Linux |
| Maturity | Young, in active development | 20+ years, battle-tested |
| License | MIT | GPL-3.0 |
Using both
Browse and edit in Citadel; drop back into Calibre for conversion or device sync whenever you need it. One caution: don't edit the same library from both apps at the same moment. Calibre treats its database as private while it's running, and concurrent writes from another program are how libraries get hurt. Close one before writing in the other.
Obligatory respect: Citadel wouldn't exist without Calibre, which is a project by Kovid Goyal and contributors. Citadel is independent, unaffiliated, and grateful. If Citadel ever writes something Calibre can't read, report it and it gets fixed as a data-safety bug.