Calibre_LogoCalibre is a free, cross-platform software, for managing digital books. Its creator is Kovid Goyal.

Its main features are:

  • Management of one or more libraries

  • Converting books in various digital formats

  • Changing the code e-books

  • Synchronization with e-readers and other e-book devices

  • Download articles from the web and editing it as e-books

  • e-Book reader

  • Content server for online access to its collection of books

A scalable, flexible and collaborative program

Calibre is a program actively monitored by a team of volunteer developers who provide weekly updates and offer additional modules that extend the functionality of Caliber.

The interface is translated into many languages by volunteers and bug reports are actively supported.

A forum, which involved Kovid Goyal and other programmers, allows users to ask questions, suggest improvements and exchange tips and tricks.

A popular program

According to the official website, Calibre has about 3.5 million users (number of computers that Calibre was used/updated in the last 2 months). On average 500,000 people install or update each month.

Connections from many countries: United States (20.3%), Spain (11.1%), Germany (8.6%), England (7.1%).

Management of one or more libraries


When a digital book is saved with Calibre, the file is saved in a directory on a particular nomenclature: Library_name / Author / Title of the book. Each own directory of a book contains:

  • the files of the book (many files that stored in different formats for the same book)
  • an image that is one of the cover (eventually taken from the book file)
  • metadata.opf file (Open Publication Format), which contains the metadata of the book (also extras from the book).

In addition, the file data base metadata.db serves the entire library. This database is updated when adding books, and when information of a book is changed through the user interface.

Note: Calibre does not handle e-books as they are, wherever they are. It duplicates thereof, change the title, change the metadata i.e. alter the content (ex .: for epub, the “content.opf, inner part of the electronic book)…. As this is not a real manager, because it is – because of its choice – unable to handle a book without duplicate in a different location than the original. This forbids him – in particular – to manage any book he can interpret/edit or copy. A manager – in essence – is supposed neutral vis-à-vis the managed data and should not change (in anything) or duplicate managed data.

User Interface

The user interface, based on metadata.db, allows:

  • sort library books,
  • filter out library books,
  • add tags and comments to characterize the books,
  • modify the content of the books,
  • convert books in another format,
  • export books to an external drive or to another directory on the computer,
  • read the books,
  • retrieve metadata and cover of a book on the internet
  • search for a book on the internet and put in touch with an online bookstore.

Book management is based on the metadata normally contained in digital books and reported in metadata.db: Title, Author, Date, Date of publication, size, series, etc. It also allows the addition of two of its own metadata: Tags and Comments.

Virtual or separate libraries

Calibre allows you to create virtual libraries, a kind of sub-libraries that are subsets of a complete library. This can be useful to treat more flexible and faster a portion of the books.

Calibre also allows multiple completely separate libraries (they are stored in different directories). A copy of a book from one library to another is planned.

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