KOReader: Open-Source eBook Reader

Original Article ↗ Hacker News Discussion ↗

Overall reception

  • Widely praised as a “best in class” reader, especially on e‑ink devices and older Kindles that have been jailbroken.
  • Users highlight that once configured, it’s hard to go back to stock firmware; some say they now choose devices based on KOReader compatibility.
  • A minority find it too complex or ultimately revert to stock software, especially on Kobo where the default is already good.

Features & reading experience

  • Strong PDF support: reflow, margin cropping, configurable overlap when panning, multi‑column reading flows, intelligent comic panel zoom, and per‑document profiles.
  • Rich reading analytics: time spent per page/chapter, overall reading timelines, and “book map” visualizations that help with technical books.
  • Extensive customization: fonts, margins, gestures, dictionaries, dark mode on older Kindles, configurable frontlight/natural light on some devices.

Performance, battery & e‑ink specifics

  • Most report similar or better battery life than stock firmware on Kindles and Kobos; one mentions KOReader being better than Amazon’s on an older Paperwhite.
  • Performance is generally good, but large EPUBs can have slow first loads or font‑size changes due to indexing; disabling full‑text indexing can help.
  • Some Android users find it snappy, others report sluggishness on powerful phones, suggesting device-/config‑dependent behavior.

Installation, platforms & jailbreak concerns

  • Runs on many platforms: Kindle (via jailbreak), Kobo, PocketBook, Supernote, Boox, Inkpalm, Android, Linux tablets, etc.
  • On Kobo and PocketBook, it can coexist with the native OS and be launched from menus, keeping OverDrive or sync features intact.
  • Experiences differ on how “trivial” Kobo install is; some find scripts easy, others found the process hacky and reverted.
  • Kindle users discuss jailbreak persistence, blocking firmware updates, and tools like WinterBreak and KUAL.

Syncing & library management

  • Common setups use Calibre/Calibre‑web, OPDS servers, self‑hosted tools (e.g., Kavita), or Dropbox/WebDAV for book delivery.
  • Progress sync is separate from file sync; users mention KOReader’s own sync server and custom servers (e.g., sync.koreader.rocks, Koofr WebDAV).
  • Some struggle to understand or fully utilize multi‑device sync; progress sync tends to be filename‑based and not fully automatic for all data.

DRM, library books & formats

  • KOReader doesn’t handle DRM or OverDrive directly; users keep native Kobo software for library loans or strip DRM via Calibre/DeDRM or similar workflows.
  • Recommended to buy DRM‑free where possible, but several mention purchasing DRM’d books and then removing DRM to keep everything in Calibre and KOReader.
  • Lack of vertical, right‑to‑left text (e.g., Japanese) support is a long‑standing unresolved issue noted as a blocker for some.

UI complexity, aesthetics & alternatives

  • Interface described as powerful but overwhelming, “wonky” or “hideous” yet highly functional; compared to tools like vi or Winamp.
  • Some argue the “clutter” is a reasonable price for exposing deep functionality; others prefer simpler readers like Moon+ Reader, Librera, FBReader, Plato, Book Story, or device defaults.
  • Keyboard and word spacing/justification aesthetics draw occasional criticism, especially for long‑form comfort and on non‑e‑ink devices.

Hackability & implementation details

  • Highly hackable: mostly Lua (with LuaJIT and FFI), making it approachable for adding features like device‑specific lighting support.
  • Build system for the emulator involves multiple tools (CMake, Meson, autotools) due to bundled dependencies.
  • Users are impressed that extensive features and custom rendering are implemented in Lua while remaining usable on constrained hardware.