Koreader

Open source alternative to Kindle and Kobo

30.7K stars
AGPL-3.0
Active this week
Last commit today

Last verified Oct 29, 2026

Run an open source document reader on Kindle, Kobo, PocketBook, reMarkable, and Android supporting PDF, EPUB, DjVu, FB2, CBZ, and a dozen other formats.

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Read the full breakdownWho it is for, how it works, trade-offs and the FAQ

who it's for

Who Koreader is for#

Academic readers with PDF and DjVu archives on e-ink devices

KOReader opens scanned PDFs and DjVu files that factory e-reader firmware cannot handle, and reflows them into a readable single-column format using K2pdfopt. Readers who download papers from arXiv or similar repositories and want to read them on an e-ink device find KOReader fills a gap no factory app covers.

Skip if:

If your reading is primarily EPUB books bought from the Kobo or Kindle stores, your device's built-in app handles those natively without the installation complexity KOReader requires.

Calibre library owners syncing wirelessly to e-ink devices

Readers who manage EPUB and PDF libraries in calibre can use KOReader's wireless server integration to push books over Wi-Fi without plugging in the device. The library metadata syncs alongside the files, and KOReader's OPDS support lets you browse the calibre catalog directly on-device.

Skip if:

If your calibre library is DRM-free EPUB and your current device firmware opens it reliably, the convenience gain may not justify the installation effort on Kindle or Kobo.

Comic readers using CBZ collections on e-ink devices

KOReader opens CBZ and CBT comic archives on Kobo, PocketBook, and Android with zoom controls suited to e-ink displays. Readers who collect DRM-free comics and prefer an e-ink screen find KOReader the most accessible option for these formats on these devices.

Skip if:

If you read primarily on an iPad or Android tablet, a dedicated color comic reader provides the color display and touch controls that KOReader on a monochrome e-ink screen cannot match.

reMarkable and PocketBook users needing wider format support

reMarkable's factory software handles PDF well but has limited EPUB rendering. PocketBook handles more formats but lacks calibre wireless sync and scanned PDF reflow. KOReader adds both to either device through a consistent installation and configuration path.

Skip if:

If you use a reMarkable primarily for handwritten notes and annotating PDFs, the factory software is adequate and KOReader adds complexity without a clear benefit.

the problem

The problem it solves#

E-reader manufacturers ship devices with reading software that supports a narrow set of formats, typically the manufacturer's own format plus EPUB. Kindle handles MOBI and AZW3 well, but not DjVu, CBZ, or scanned PDFs with reflow. Kobo has broader support but still falls short on typesetting controls. The factory firmware is designed to sell books through the manufacturer's storefront, not to open files from any source.

The deeper problem is that many readers accumulate files the factory firmware cannot handle: academic papers in PDF or DjVu, comic collections in CBZ, calibre-managed EPUB libraries, or files bought outside the device's ecosystem. Long reading sessions on e-ink screens also require fine typographic adjustments, page margins, line spacing, and font choices that factory apps do not expose. Readers working across multiple file sources and formats end up converting files through calibre just to open them, or missing formats the device cannot read at all.

how Koreader solves it

How it solves it#

Multi-format document support

Opens PDF, EPUB, DjVu, FB2, Mobi, DOC, RTF, HTML, CHM, TXT, CBT, and CBZ files. Fixed-page formats like PDF and DjVu display with zoom and contrast controls; reflowable formats like EPUB and FB2 flow to the screen with full typographic customization.

Scanned PDF and DjVu reflow

Scanned PDFs and DjVu documents can be reflowed into a readable single column using the bundled K2pdfopt library. This converts two-column academic papers or old scanned books into paginated text that fits the e-ink display without horizontal scrolling or zooming.

Calibre library integration

Connects to a calibre wireless server to search metadata and receive books over Wi-Fi without a USB cable. Also supports browsing libraries via OPDS catalogs and RSS feeds for fetching content from external sources, including Wallabag and Wikipedia.

E-ink optimized interface

Custom UI built for e-ink displays: no animation, paginated menus, and adjustable text contrast. Page-turn speed on older devices has been measured at less than half the delay of the built-in reading software, according to the project README.

Deep typographic control

Set custom page margins, override line spacing, choose external fonts, and apply multi-lingual hyphenation dictionaries covering over 30 languages. Settings persist per document, so each book carries its own display configuration across reading sessions.

strengths · trade-offs

Strengths and trade-offs#

Strengths

Broader format coverage than factory firmwareOpens 12+ formats where Kindle's built-in software handles 3-4 and Kobo handles around 8. DjVu, CBZ/CBT, and scanned PDF reflow are not available in either factory app. Readers with calibre libraries or academic PDF and DjVu collections gain access to their full archive without format conversion.
Runs on 7+ device platforms from one codebaseThe same application runs on Cervantes, Kindle, Kobo, PocketBook, reMarkable, Android, and Linux. A reader who switches hardware keeps the same reading software and configuration. No other open source ebook reader covers this hardware range.
AGPL-3.0 license and 13 years of active developmentLicensed under AGPL-3.0 and in continuous development since 2013, with over 30,000 GitHub stars and an active community forum on MobileRead. The project offers over-the-air software updates on supported devices and accepts contributions via GitHub.
Calibre wireless sync without USBReceives books from a calibre wireless server on the same Wi-Fi network without a cable, with metadata syncing alongside files. This surpasses both Kindle and Kobo native workflows, which require USB cable or cloud sync through a manufacturer account.

Trade-offs

-Kindle installation requires jailbreakInstalling KOReader on a Kindle requires jailbreaking the device first, which voids the warranty and is firmware-version dependent. Amazon pushes firmware updates that can break the jailbreak, so Kindle users typically disable automatic updates after installing. Kobo and reMarkable installs are less involved.
-No DRM supportKOReader does not handle DRM-protected files from Amazon, Kobo, or other stores. Books purchased through Kindle or Kobo with DRM cannot be opened directly. Readers who rely on DRM-protected purchased books from either storefront cannot use KOReader as a full replacement for their factory app.
-Device-specific installation steps per platformInstallation varies by device and requires following multi-step wiki procedures. Each device has its own method: file copy for Kobo, APK for Android, jailbreak process for Kindle, and a separate procedure for reMarkable. There is no universal one-step installer across platforms.

versus alternatives

Koreader vs alternatives#

KOReader vs Kindle Reading Software

Kindle's built-in reading software handles AZW3, MOBI, and EPUB but does not open DjVu, CBZ, FB2, or most other formats KOReader supports. Typographic controls are limited to Amazon's licensed fonts, and margin adjustments have a narrow range. Sideloading books requires sending files via email or USB; there is no calibre wireless support.

KOReader on a jailbroken Kindle adds DjVu, CBZ, CBT, FB2, DOC, RTF, HTML, and CHM support, along with calibre wireless sync, custom external fonts, and scanned PDF reflow via K2pdfopt. The trade-off is the jailbreak requirement: installation depends on device model and firmware version, and Amazon firmware updates can break it.

Feature	KOReader	Kindle Software
License	AGPL-3.0	Proprietary
DjVu support	Yes	No
CBZ/CBT support	Yes	No
Scanned PDF reflow	Yes (K2pdfopt)	No
Calibre wireless sync	Yes	No
Custom fonts	Yes (external)	Limited
DRM books	No	Yes (Amazon)
Installation	Requires jailbreak	Pre-installed

Kindle's built-in software is the better choice for readers who buy books through Amazon and need DRM support. KOReader on Kindle makes sense for readers with calibre libraries or files in formats Kindle firmware cannot open.

KOReader vs Kobo Reading Software

Kobo's factory firmware handles EPUB, PDF, MOBI, CBR, and CBZ, giving it broader default coverage than Kindle. Kobo also supports calibre USB sync natively. KOReader's advantages over Kobo firmware include scanned PDF reflow with K2pdfopt, DjVu support, finer typographic controls, calibre wireless sync instead of USB only, and over-the-air updates.

Kobo installation is straightforward: KOReader is placed on the device storage and Kobo's factory reader launches it as an alternative application without requiring a jailbreak.

Feature	KOReader	Kobo Software
License	AGPL-3.0	Proprietary
DjVu support	Yes	No
Scanned PDF reflow	Yes (K2pdfopt)	No
Calibre wireless sync	Yes	USB only
Custom external fonts	Yes	Limited
DRM books	No	Yes (Kobo)
Installation	File copy, no jailbreak	Pre-installed

Kobo's built-in software is the better choice for readers who buy through Rakuten Kobo and want DRM support with no setup. KOReader on Kobo makes sense for calibre users, PDF-heavy readers, or anyone with DjVu or CBZ files outside the Kobo storefront.

tech stack · detected from GitHub

What it's built on#

Languages: Lua

frequently asked

FAQ#

Does KOReader work on my Kindle?

KOReader runs on most Kindle models, but installation requires jailbreaking the device first. The project wiki documents the steps for each model and firmware version. Note that Amazon may push firmware updates that break the jailbreak, so most users disable automatic updates after installing KOReader.

Can KOReader open DRM-protected books from Amazon or Kobo?

No. KOReader has no DRM support and cannot open DRM-protected files from Amazon or Kobo. Readers who want to use purchased books from either storefront need to remove DRM first using a separate tool. KOReader is designed for DRM-free files from calibre libraries, open access archives, or personal collections.

Is KOReader free to use?

Yes. KOReader is licensed under AGPL-3.0 and free to download, install, and use on any supported device. The project accepts donations through Liberapay but there is no paid tier or required account. All features are available at no cost.

Does KOReader replace the built-in reading app on Kindle or Kobo?

On most devices, KOReader runs alongside the factory reader rather than replacing it. On Kobo, it launches as an alternative from within Nickel (the default reader). On Kindle, it runs as a separate application after jailbreaking. The factory software continues to handle DRM books and features outside KOReader's scope.

What is PDF reflow and when should I use it in KOReader?

PDF reflow converts a fixed-layout PDF, such as a scanned academic paper or a two-column textbook, into a single flowing column that fits the e-ink display without zooming or horizontal scrolling. KOReader uses the K2pdfopt library for this. Reflow works best on text-heavy PDFs; image-heavy documents or PDFs with complex layout are better read in the default PDF view.

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KOReader vs Kindle Reading Software

Feature	KOReader	Kindle Software
License	AGPL-3.0	Proprietary
DjVu support	Yes	No
CBZ/CBT support	Yes	No
Scanned PDF reflow	Yes (K2pdfopt)	No
Calibre wireless sync	Yes	No
Custom fonts	Yes (external)	Limited
DRM books	No	Yes (Amazon)
Installation	Requires jailbreak	Pre-installed

KOReader vs Kobo Reading Software

Kobo installation is straightforward: KOReader is placed on the device storage and Kobo's factory reader launches it as an alternative application without requiring a jailbreak.

Feature	KOReader	Kobo Software
License	AGPL-3.0	Proprietary
DjVu support	Yes	No
Scanned PDF reflow	Yes (K2pdfopt)	No
Calibre wireless sync	Yes	USB only
Custom external fonts	Yes	Limited
DRM books	No	Yes (Kobo)
Installation	File copy, no jailbreak	Pre-installed