Calibre is a free, open-source e-book manager for Windows, macOS and Linux, and it can also run from a USB stick. It keeps a personal collection of e-books in one library, edits their metadata and converts them between formats. It also sends them to e-readers, phones and tablets, and opens them in its own reader.
Library folders and book records
Calibre stores its collection in a library folder. Calibre copies every book added afterwards into this folder and files it in subfolders by author and title. It keeps titles, authors, series, tags and ratings in a database at the top of the folder. Each book folder also holds a small metadata file, so the database can be rebuilt if it is damaged. Users can keep several libraries and switch or copy books between them. Users should only change files in the library folder through Calibre. The library should not sit on a network drive.
One record can hold several formats of the same title, such as EPUB and AZW3, along with a cover. Books arrive from single files, folders searched recursively, ZIP, RAR or 7z archives, or a list of ISBNs. Calibre reads their metadata from the file contents or, optionally, from the filename.
Editing and downloading metadata
The metadata editor covers title, authors, series, tags, rating, publisher, identifiers, description and cover. Calibre can search online by title and author, or by ISBN when one is entered. It can list the closest matches and fill in fields such as series, tags, description and cover from the chosen result.
For many books at once, the bulk editor applies one value to a field across the selection. It offers search and replace, including regular expressions, to clean up names or copy values from one field to another. Users can also add their own columns, for example to track which books they have read.
Finding books in a large collection
The search bar accepts plain words or a query language. This language matches fields exactly, by regular expression or by comparison, and combines terms with and, or and not. A single query can find books rated three or higher, books added in the last week, or books without a cover. Users can save useful queries by name. Virtual libraries turn a query into a permanent subset, such as one genre, without splitting the library itself.
Full-text search is an opt-in index that lets Calibre find a phrase inside the books rather than only in their metadata. The Tag browser beside the book list groups the collection by categories such as authors, series and tags. Clicking an item filters the list to matching books.
Format conversion
Calibre reads formats including EPUB, AZW3, MOBI, KEPUB, PDF, DOCX, ODT, RTF, HTML, TXT, FB2 and comic archives. It writes EPUB, AZW3, MOBI, KEPUB, DOCX, PDF, RTF, FB2, TXT and several older reader formats. Every conversion follows the same route: Calibre turns the source into XHTML, transforms it, then writes it out in the target format. That middle stage is where Calibre can rescale fonts, change justification and paragraph spacing, add CSS, detect chapters and build a table of contents. Optional heuristics repair text with broken lines and unformatted headings, which is common in material from PDFs or scans.
Users can convert books one at a time, and Calibre remembers the settings for each book. They can also convert books as a batch with shared settings. Calibre does not convert books protected by DRM. PDF is the weakest source: multi-column pages, tables, images of text, links and right-to-left text do not convert reliably.
Transfer to e-readers and phones
When a supported e-reader, phone or tablet is connected, Calibre shows its contents next to the library and copies books in either direction. Sending a book picks the format the device reads best and converts it on the way if needed. Users can use a reader that appears as an ordinary USB disk through Connect to folder. Apple devices do not connect by USB and use the web server instead. Users can also send books by email.
The E-book viewer
Calibre’s viewer opens all major e-book formats. It shows text either as pages or as one continuous flow, with adjustable fonts, colors, margins and pages per screen. Readers move through the book with the table of contents, bookmarks and in-book search, which can match whole words, nearby words or regular expressions. Selecting text offers highlights, notes and dictionary lookup. Readers can browse highlights from every book together from the library. Read aloud speaks the text and marks the current sentence.
Editing EPUB and AZW3 files
The Edit book tool opens EPUB, KEPUB and AZW3 files and exposes the HTML, CSS and images inside them. It includes a code editor and a live preview that follows the cursor. Renaming a file updates every link to it. Users can split, merge or reorder files. Search and replace works across all files with plain text, regular expressions or small Python functions. Check Book reports broken links, malformed markup and invalid CSS and repairs many of them automatically. Other tools edit the table of contents, smarten punctuation, embed or subset fonts and run a spell check. Checkpoints let users return to an earlier state of the book.
News downloads
Calibre turns news sites into e-books through recipes. Hundreds of built-in recipes cover major newspapers and magazines. Users can schedule downloads by weekday or interval. Each issue lands in the library and on a connected reader. A custom source needs only a title, RSS feed addresses, a maximum article age and an article count per feed. An advanced mode exposes the recipe as Python code for removing page clutter or logging in to subscription sites.
Content server
The Content server makes the library available to other devices over the local network or the internet. Any web browser can browse covers, search, download books or read them in the page. The reading position syncs between devices. A loaded book stays readable offline, and reading apps can connect through OPDS. Users can protect access with a username and password. The server can also run on its own on a machine without a desktop.
Plugins and AI
A built-in plugin browser installs additional functions from a large catalogue of plugins. Optional AI features remain inactive until a cloud or local provider is configured. They can suggest what to read next or explain, translate and summarize a passage selected in the viewer.
