calibre

Project Overview

calibre is maintained by Kovid Goyal and a group of volunteers, and it is the most platform-complete toolkit in e-book management. It puts library management, format conversion, metadata download, news-to-ebook recipes and reader sync into one desktop application; the source is released under GPL-3.0 and the interface runs on Python and PyQt6.

A library is a folder tree of book files, with metadata collected in metadata.db, a SQLite database at the top level of the library folder, so backing up means copying that whole folder. Conversion is a pipeline: an input plugin turns the file into XHTML, then an output plugin builds the target format.

Item	Value
Current version	9.18.0
Platform	Windows, macOS, Linux
Stack	Python 3.14+, PyQt6 6.10.0
Conversion plugins	23 input plugins, 17 output plugins
License	GPL-3.0-only

Install one program and you get a library, a converter, an editor, a viewer and a content server.

Key Features

• Format conversion: the GUI and ebook-convert share one plugin set covering EPUB, MOBI, AZW3, PDF, DOCX, FB2, HTMLZ, LIT, LRF, PDB, PML, RB, RTF, SNB, TCR, TXT and more
• Library management: each book keeps its metadata, cover and format files in the library folder, with metadata written to metadata.db
• Virtual libraries: save a set of search terms as a virtual library and type vl:name to show only that subset
• Full-text search: builds an index so you can search the body text of every book in the library
• Metadata download: fills in title, author, publisher, rating and description in bulk by title, author or ISBN
• E-book editing: the built-in editor changes body text, styles and the table of contents of EPUB and AZW3 files
• Viewer: ebook-viewer offers paging, a table of contents, search plus font and color adjustments
• News recipes: turns sites or RSS feeds into formatted e-books and downloads them on a schedule
• Device sync: sends books to Kindle, Kobo and similar readers by author, tag or series and manages the device library
• Content server: calibre-server publishes the library as a web page for reading and downloading in a browser

Library and Interface

The main window is the book list: the tag browser on the left filters by author, language, series or format, the middle switches between list and cover grid, and the right pane shows the cover and metadata of the selection. Virtual libraries and saved searches sit above the tag browser as separate views, while the toolbar gathers add books, edit metadata, convert books, view and send to device.

The conversion dialog groups its options into look and feel, page setup, heuristic processing, search and replace, structure detection and table of contents, matching the ebook-convert command-line switches.

Module	Purpose
Library	Browse by category, search and batch-edit metadata
Convert	Single or batch conversion with reusable presets
Edit book	Change the internals and styles of EPUB / AZW3
Viewer	A separate reading window with contents, search and colors
Jobs	Follow background batch conversions and metadata downloads

Target Audience

• Collectors with thousands of e-books
• Readers who batch-convert formats
• Users running their own book server
• Editors doing e-book layout work
• Kindle and Kobo owners

Quick Start

1. Install the package for your platform: calibre-64bit-9.18.0.msi on Windows, calibre-9.18.0.dmg on macOS, calibre-9.18.0-x86_64.txz on Linux
2. Choose a library folder in the first-run wizard; every imported book lands there
3. Drag e-books into the library window, or use Add books for a batch import
4. Select a book, click Convert books, pick EPUB or AZW3 as the output format, then adjust page setup and the table of contents
5. Use Edit metadata to download covers and descriptions in bulk, or by ISBN for one book
6. Select books and click Send to device to push them to a connected reader

Command-Line Tools

Command	Purpose
ebook-convert	Convert one file with the same options as the GUI
calibredb	Add, remove, edit and list library records in bulk
ebook-viewer	Open the reader window
calibre-server	Start the content server, with --port for the listening port
calibre-debug	Debug entry point for running scripts or inspecting the environment

System Requirements

Item	Requirement
OS	Windows, macOS, Linux
CPU	Official packages for x86_64 and arm64
Python	3.14+ when running from source
GUI dependencies	PyQt6 6.10.0, PyQt6-WebEngine 6.10.0
Package size	About 291 MB for the Windows MSI, 406 MB for the macOS DMG

Notes

• The converter is not a layout tool: complex layouts, footnotes and floats can shift during conversion, so convert to EPUB first and fix the result in the editor
• PDF input is limited: PDF text is reflowed from the text layer, and scanned pages need OCR before they are usable
• Do not touch the library folder: book files and metadata.db are managed by the program, and renaming things by hand breaks the records
• Running from source is heavy: many dependencies are pinned, while the official packages bundle Qt and Python