citadel: Open Source Publishing

What is citadel?

What it is

Citadel is a desktop application for managing ebook libraries, written in Rust and released under the MIT license. It is positioned inside the Calibre ecosystem as a backwards-compatible manager for ebook collections, with the stated goal that Calibre must be able to read any library that Citadel has edited. The project targets users who want a faster and easier-to-use interface for organizing ebooks, especially epub files, without replacing the Calibre library format.

The concrete problem Citadel addresses is the friction of managing an ebook collection with an existing Calibre library. Its README states that Citadel should feel much faster than Calibre and never slower, while remaining compatible enough that Calibre can still open the edited library. The project avoids becoming an ebook reader or an editor of ebook content, so it focuses on library organization and metadata rather than reading or modifying files inside ebooks.

Key capabilities

Citadel maintains Calibre-compatible ebook libraries, so Calibre can read a library after Citadel edits it.
It manages ebook collections and epub files rather than acting as an ebook reader.
It opens ebook files in the user's default applications instead of embedding a reader inside Citadel.
It provides automatic update checks that can be disabled in Settings, while installs require an explicit action.
It distributes stable builds through GitHub Releases and development builds through GitHub Actions.

Who uses it and how

Users who already keep ebooks in Calibre can use Citadel as a compatible manager for metadata and collections.
Readers who prefer external ebook apps can use Citadel to manage files and then open them in their default applications.
macOS users can install stable builds from a downloaded .dmg by dragging Citadel into Applications.
Contributors can install Bun and Rust, run bun install, and start the app with bun run dev or bun run build.

Getting started

Stable builds are downloaded from GitHub Releases, with a macOS .dmg installed by dragging Citadel to Applications; development builds are available from GitHub Actions. For source use, install Bun and Rust, run bun install, then use bun run dev or bun run build.

When to use it — and when not to

Use Citadel when you need a Calibre-compatible desktop manager for ebook collections and want to keep Calibre as the library format while using a different interface. Do not use it as an ebook reader, as a content editor, or as a complete replacement for Calibre’s plugins and advanced features, because the README states those are non-goals or unlikely. The repository is three years old, has ten open issues, and lists no contributor count; development builds are unsigned on macOS, so users must remove quarantine attributes and install updates explicitly.

project readme (upstream, from github) — read inline

Citadel

Manage your ebook library with Citadel. Backwards compatible with Calibre.

https://github.com/user-attachments/assets/7db593a9-2095-4ac9-8f38-45107cc059dd

Project goals

Backwards compatible with Calibre: Calibre must be able to read any library that Citadel has edited.
Good UX: Citadel must be easy to use and look good.
Performant: Citadel must feel much faster than Calibre, and never slower.

Non-goals

Ebook reader: Citadel is not an ebook reader. There are already excellent ereader apps: Citadel will open your files in your default apps.
...or editor: If you're editing ebook content (not metadata like titles), Citadel will not be a replacement for you.
100% feature parity: Primarily around Plugins, but there are some advanced features of Calibre we'll likely never build.

Downloading

Stable builds are available in Releases.

Development builds are available from GitHub actions.

Please report any issues or crashes you experience while using any version of Citadel!

Installing on macOS

Download the .dmg from Releases, drag Citadel to Applications, and open it.

[!NOTE]

Development builds from GitHub Actions are not signed. macOS will report those as "damaged"; removing the quarantine attribute resolves this:
xattr -d com.apple.quarantine /Applications/Citadel.app/

Developing

As a prerequisite, you'll need to install Bun and Rust.

Then, you can install the packages.

bun install

and start up the app like so:

bun run dev
# or just bun dev

Lint & Formatting

To lint all source code, run bun lint. To autoformat, run bun format.

Scope	Action	Command
All code	Format	`bun format`
All code	Format (Check)	`bun format:check`
All code	Lint	`bun lint`
Backend	Format	`bun format:backend`
Backend	Lint	`bun lint:backend`
Frontend	Format	`bun format:web`
Frontend	Lint	`bun lint:web`

App preview without backend

You can run just the frontend with this command, although you WILL see errors as the Rust backend will be missing but is assumed to exist:

bun dev:app

Building

To create a production version of Citadel, you'll need the development prereqs. Then:

bun install
bun run build

Auto-updater and releases

Citadel can check for app updates and install them on request. Automatic update checks can be disabled in Settings (Auto updates: On/Off), and installs are always explicit (Install and restart). For maintainer setup and release workflow details, see docs/updater-and-releases.md.

Additional Credit & Related Projects

This project would not be possible without the north star created by Kovid Goyal, Calibre. Without his hard work building such an extensive and powerful tool, Citadel would not exist.

Huge thanks to Kemie Guaida, who created an excellent Calibre redesign Figma prototype, from which Citadel takes inspiration. Thank you, Kemie!

Frequently asked questions

Is citadel free to use?

citadel is open source under the MIT licence. There is no licence fee and no seat count — you can self-host it or, where the project offers one, pay a vendor for a managed version instead.

What does citadel do?

Manage your ebook library without frustrations. Calibre compatible.

What is citadel written in?

citadel is primarily written in Rust. Its source is publicly available at https://github.com/everydaythingssoftware/citadel, and it has 1,276 GitHub stars.