cbooks

A free EPUB reader that runs in your web browser. Your notes and your place stay on your device, and it works offline.

Open the reader

What it is

cbooks (also called the cbook reader) opens books in the EPUB format on a phone, a tablet or a computer. It is a web page, so there is nothing to install and no sign-in. Open it in a browser and start reading.

What you can do

• Keep a library of EPUB books in your browser, with covers and your progress, and continue where you left off.
• Highlight passages and write notes on them. A note is re-found by the words of the passage, so it can follow you to a newer edition of the same book.
• Keep a Trail: a record of where you read, which you can download as a backup.
• Change the layout and font size, jump by contents, search, and go back and forward along your path through the book.
• Read offline. The first visit with a connection saves the reader itself in your browser, after that it opens with no signal.

Privacy

Books you add from your own device are read in the page and are never uploaded. Your library, notes, highlights and reading place are kept in your own browser storage, not on a server. The reader has no accounts. Clearing your browser's site data removes them, so use Download trail to keep a copy.

Books to try

The library includes a short Getting started guide and two featured books, Adventure and Learning of Voyager 1 and Mercury to Atlas, written by Claude (an AI) at the direction of Bill Mandel. A book you get from a link can update itself when a new edition is published, and your notes carry across.

Make your own book

You can make a book with an AI assistant in about fifteen minutes and read it in cbooks. The Make a book page walks through it. The guides are plain text you can give to an assistant:

• Authoring guide (Markdown)
• Guide for making a book from PDFs (Markdown)

How it was built

cbooks was built by Bill Mandel with Claude Code, Anthropic's AI coding assistant. It was first built in November 2026. Claude Code wrote the reader's code, its offline support and its automated tests, working from Bill Mandel's directions and his testing on an Android phone.

The reader is plain web files: about 3,500 lines of its own JavaScript, plus HTML and CSS. It uses the open-source foliate-js engine (MIT licence) to display books, pinned to one version. There are 28 automated test scripts with more than 400 checks that run in headless Chrome. They cover things like offline use, page turning, and re-finding your notes after a book is changed.

Claude also wrote the two featured books, and the Make Book page gives an AI assistant, Claude or Gemini, the guide it needs to build a book for you.