KOReader — Document Viewer for E-Ink Devices and Beyond

Introduction

KOReader is a document viewer built primarily for e-ink devices but also available on Linux and Android. It provides an experience tuned for long reading sessions on low-refresh-rate displays, with extensive typesetting controls that go far beyond the stock readers shipped by device manufacturers.

What KOReader Does

• Renders PDF, EPUB, DJVU, CBZ, FB2, DOC, and dozens of other document formats
• Reflows PDF text to fit e-ink screens, eliminating horizontal scrolling on small displays
• Provides granular control over fonts, margins, line spacing, word spacing, and hyphenation
• Supports dictionary lookup, Wikipedia integration, and translation within the reader
• Syncs reading progress across devices via a built-in progress sync server or Calibre

Architecture Overview

KOReader is written in Lua and C, using the MuPDF and CREngine rendering backends. MuPDF handles PDF and image formats while CREngine handles EPUB and other reflowable formats. The UI framework is custom-built for minimal memory usage and fast partial-refresh rendering on e-ink panels. Plugins extend functionality without modifying the core, and the Lua scripting layer makes it accessible for user customization.

Self-Hosting & Configuration

• Install on Kindle, Kobo, PocketBook, reMarkable, and Android devices via sideloading
• Run on desktop Linux as an AppImage or Flatpak
• Configure page-turn gestures, swipe zones, and button mappings per device
• Use the built-in OPDS browser to connect to Calibre or other eBook servers
• Set up KOSync server for reading-position synchronization across multiple devices

Key Features

• PDF reflow mode that reformats fixed-layout pages for small screens
• Fine-grained typesetting controls rarely found in other e-reader software
• Plugin system with SSH, FTP, cloud storage, RSS, and Wallabag integration
• Extremely low memory footprint suited for resource-constrained e-ink devices
• Active development with frequent releases and broad device support

Comparison with Similar Tools

• Stock Kindle/Kobo reader — limited customization; KOReader offers far deeper typesetting and format support
• Koodo Reader — designed for desktop and web; KOReader is optimized for e-ink hardware
• Calibre — library management tool; KOReader is a reader with on-device controls
• Foliate — Linux desktop EPUB reader; KOReader runs on e-ink devices and mobile
• Moon+ Reader — Android-only; KOReader works on e-ink devices, Android, and Linux

FAQ

Q: Will installing KOReader void my e-reader warranty? A: KOReader runs alongside the stock software on most devices. It does not require rooting on Kobo or PocketBook. Kindle requires jailbreaking.

Q: Can I use my own fonts? A: Yes. Place TTF or OTF files in the fonts directory and select them in the reader settings.

Q: Does it support annotations and highlights? A: Yes. Highlights and notes are stored locally and can be exported as JSON, Markdown, or plain text.

Q: How do I sync progress between devices? A: Use the built-in KOSync plugin, which connects to a self-hosted or community KOSync server.

Sources

• https://github.com/koreader/koreader
• https://koreader.rocks