EPUB reader

What it shows

• The book's details from its package file: title, author and other creators with their roles (translator, illustrator, editor), language, publisher, date, identifier (usually an ISBN or a UUID), the description, whether it is EPUB 2 or EPUB 3, and the cover picture.
• The table of contents exactly as the book defines it, nested as deep as it goes: parts, chapters and sections. Click an entry to open that chapter at that heading. A book without a table of contents gets its reading order instead.
• The chapters with the book's own images, stylesheets and fonts, taken from inside the file. Links between chapters and to footnotes move through the book; “Chapter 2 of 14” shows where you are, and the ← and → keys turn chapters.
• Text size from 70 % to 200 %, and dark mode when your device is set to dark: the book's colours are replaced by light text on a dark page.
• Nothing loads from the web. A book can contain scripts and references to remote images or stylesheets. Here, scripts never run, and anything remote is blocked and counted under the chapter. Web links in the book open in a new tab only when you click them.

What it cannot do

• DRM-protected books. Books bought from Kobo, Google Play Books, Apple Books or many other shops, and library loans, are often encrypted so that only the shop's app can open them. The page recognises this, from an encryption.xml that encrypts chapters or an Adobe rights.xml, Apple sinf.xml or Readium LCP licence, shows the book's details, and tells you to open it in the app you bought it in. It never tries to remove DRM.
• Kindle files. AZW, AZW3, KFX and MOBI are Amazon formats, not EPUB, and are not read here. A DRM-free MOBI or AZW3 can be converted to EPUB in Calibre (see below).
• Page-by-page layout. Each chapter is one scrolling page, with no page numbers matching the print edition. Fixed-layout books (comics, picture books, some cookbooks) open, but each page is shown as a scrolling document and two-page spreads are not paired.
• Interactive books. Scripts inside a book never run, so quizzes, animations and other interactive parts of an EPUB 3 do not work. Read-aloud with highlighted text (Media Overlays) is not supported either.
• Remembering your place. Nothing is stored, so there are no bookmarks, notes or last-read position. Closing the tab forgets the book.
• Text size in every book. The control scales text the book sizes relative to the page, which most books do. A book that fixes its sizes in pixels keeps them.
• Obfuscated fonts. Some publishers scramble embedded fonts so they cannot be copied out. That is not DRM, and the book opens, but those fonts are skipped and the text shows in a standard font.
• Very large books. The whole file is read into this tab's memory. A 50 MB illustrated book is fine on a laptop; a 500 MB one may be too much for an older phone.

Useful to know about EPUB files

An EPUB is a ZIP of web pages

Rename book.epub to book.zip and any unzip tool opens it. The first file, mimetype, holds the text application/epub+zip stored uncompressed, which is how readers (and viewhack's front page) recognise the format from its first bytes. META-INF/container.xml points to the package file (.opf), which lists every file in the book (the manifest), the order to read the chapters in (the spine) and the title, author and other details. The chapters themselves are XHTML files with CSS, the same as web pages.

EPUB 2 and EPUB 3

EPUB 2 (2007) has chapters in XHTML 1.1 and its table of contents in a separate toc.ncx file. EPUB 3 (2011; version 3.3 became a W3C Recommendation in 2023) uses HTML5, puts the table of contents in an ordinary HTML page with a <nav> element, and adds audio, video, MathML, fixed layouts and scripting. Many EPUB 3 books also carry a toc.ncx so older readers can show their contents. This page reads both kinds and prefers the EPUB 3 contents when a book has both.

Getting a DRM-free EPUB

Look for “DRM-free” on the shop's page before you buy. Kobo and Google Play Books let you download an EPUB for DRM-free titles; for protected ones you get a small .acsm file instead, which is only a download ticket for Adobe Digital Editions, not the book. Humble Bundle, many small presses and some big publishers sell DRM-free, and Project Gutenberg and Standard Ebooks give away public-domain books as EPUB.

Converting in Calibre

Calibre is a free e-book manager for Windows, macOS and Linux. Add a DRM-free MOBI, AZW3 or DOCX, choose Convert books, set the output format to EPUB, then right-click the book and choose Open containing folder to find the .epub. Calibre refuses to convert DRM-protected files.

Why an e-book can contain a script

EPUB 3 allows JavaScript for interactive books, and a chapter can also point at images or stylesheets on the web. A reader app that shows them tells the other server that the book was opened. Here the chapter frame blocks both, so reading a book makes no request to anyone.