Thorium Reader — The Best Free Accessible EPUB Reader (2026 Guide)
Thorium Reader is a free, open-source EPUB reader developed by EDRLab. It's the most accessible EPUB reader available, supports EPUB 3 fully, and runs on Windows, macOS, and Linux.
What Is Thorium Reader?
Thorium Reader (thorium-reader.edrlab.org) is an open-source EPUB 3 reading application funded by the European Digital Reading Lab (EDRLab) — a non-profit consortium of publishers, libraries, and accessibility organizations. It's the reference implementation for EPUB 3 accessibility and is maintained by the people who write the EPUB specification.
Thorium Reader is notable because:
- It's the only EPUB reader certified for full WCAG 2.1 and EPUB Accessibility 1.1 compliance
- It supports EPUB 3.3, the current spec version, including MathML, multimedia, and JavaScript
- It's free, no account required, and has no file syncing or telemetry
- It works with screen readers (NVDA, JAWS, VoiceOver) without any configuration
Installing Thorium Reader
- Windows: Download the installer from thorium-reader.edrlab.org or install from the Microsoft Store. Also available via winget:
winget install EDRLab.ThoriumReader - macOS: Download the .dmg from thorium-reader.edrlab.org. Apple Silicon (M1/M2) native build available.
- Linux: Download the AppImage or .deb package.
sudo dpkg -i thorium-reader.deb - Mobile: Thorium Reader does not have iOS or Android apps. For mobile, use Readium Mobile (iOS/Android), which shares the same rendering engine.
Key Features
Reading Experience
- Paginated and scroll modes: Switch between paginated (book-like) and continuous scroll reading.
- Font and layout customization: Adjust font size, font family, line height, letter spacing, word spacing, column count, and margins. Includes dyslexia-friendly fonts (OpenDyslexic).
- Reading themes: Day, sepia, night, and high-contrast modes. Full custom color control.
- TTS (Text to Speech): Built-in TTS with sentence highlighting. Uses system TTS voices.
Accessibility
- Full keyboard navigation — no mouse required for any function
- Screen reader support via ARIA landmarks and semantic HTML
- Reads EPUB accessibility metadata and displays it ("This book has been certified accessible")
- Supports EPUB 3 Media Overlays (synchronized text highlighting with audio)
Library Management
- Drag-and-drop EPUB import
- Opds catalog support (import from library catalogs like OverDrive, Bibliovie)
- LCP DRM support (Lightweight Content Protection — the open DRM standard used by libraries)
- Annotations, highlights, and bookmarks with export
Thorium Reader vs Other EPUB Readers
| Feature | Thorium | Calibre | Apple Books |
|---|---|---|---|
| EPUB 3 support | ✓ full | partial | ✓ full |
| WCAG 2.1 certified | ✓ | ✗ | partial |
| Screen reader support | ✓ excellent | ✗ | ✓ good |
| LCP DRM | ✓ | ✗ | ✗ |
| Windows / Linux | ✓ | ✓ | Mac/iOS only |
| Book conversion | ✗ | ✓ | ✗ |
| Free / open source | ✓ | ✓ | ✓ (Apple only) |
Who Should Use Thorium Reader?
- Accessibility professionals: Testing EPUB accessibility — Thorium is the reference reader for EPUB 3 accessibility spec conformance.
- Libraries and institutions: LCP DRM support makes it the standard reader for library EPUB loans (OverDrive, BiblioVie).
- EPUB publishers: Validate how your EPUB renders in a spec-compliant reader before distribution.
- Windows/Linux users: Who don't have access to Apple Books and want a full-featured EPUB 3 reader.
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