[APP] ClickBook - free offline EPUB reader that explains any word you tap

[clickbook]

Hi all,

I'm the developer of ClickBook, a free reader app for Android (also on iPhone and iPad). I built it for one situation: reading a book in a language you are still learning, and actually enjoying it, instead of reaching for a dictionary every few lines.

What it does
You open your own EPUB (or a PDF that contains real text) and read as usual. When you hit a word you don't know, tap it. A small panel shows a short, plain explanation of what the word means in that exact sentence, plus an example. Close it and you are back on the same line.

The explanations come from a small language model running on the phone itself (a quantised Gemma 4 E2B, run with llama.cpp). No server is involved, so your books and the words you look up stay on the device.

The practical details

• Free. No account, no ads, no trackers (Exodus Privacy report)
• Works offline, airplane mode included, once the model is on the phone
• Google Play delivers the model with the app, about 1.9 GB, so use Wi-Fi and keep about 2 GB free. An app update can occasionally download it again
• Android 7.0 or later, but running a language model is demanding: I test on a Pixel 9, and older or low-memory phones will be slow or may not cope. I haven't tested it on e-ink Android readers such as Boox
• Opens EPUB, and PDFs that contain real text (they are converted on import so you can change font and size; scanned PDFs won't work)
• Four built-in fonts, adjustable size and line spacing, white, sepia, mint and dark pages, page-by-page or continuous scrolling
• Every word you tap goes into a vocabulary list, together with the sentence you found it in
• Three public-domain classics are included, so there is something to read straight away

Free explanations come in the language of the book. An optional Pro upgrade, a one-time purchase of about US$13 (local prices vary, no subscription), adds the word explained in your own language (41 languages to choose from), a translation of the passage around it, and an "Ask ChatGPT" button. That button is the only thing that ever sends text off the phone, only when you tap it, and the app asks first.

What it is not
It is not a do-everything reader like Moon+ or KOReader: no custom font import, no highlights or notes, no text-to-speech, no OPDS catalogues, no cloud sync, no DRM-protected books. And the explanations are written by an AI model, so they are usually right but can occasionally miss. If you catch one that is wrong, I would genuinely like to see it.

Google Play: https://play.google.com/store/apps/d...ickbook.reader
Website, FAQ and a free library of 403 public-domain books sorted by reading level: https://clickbook-ai.com

I'm a solo developer in Germany and I'll be following this thread. Bug reports, wrong explanations and feature requests are all welcome here or at support@clickbook-ai.com.