Uses spaced repetition to help you remember new words.
Found under top menu's Search tab when enabled (on by default).
(This wiki page describes the plugin coming with KOReader version 2022-10.)
Gather new words
Toggle automatic/manual collecting words by the Auto add new words switch from the plugin's menu (top left button).
When set to automatic, any new words looked up when using KOReader is automatically added. When set to manual, a Add to vocabulary builder button will be shown on the dictionary window for adding looked up word.
Review words
When the due time to review a word has passed, two buttons Forgot and Got it will be shown on its entry. Tap Forgot if you cannot recall the word or tap Got it if you can. Then the study status is updated and a next review time is set based on your choice.
If you are unsure of the word, tap on its entry to bring up the dictionary window. You can then decide on which button to choose within the dictionary window.
Word context
Switch on the Save context option in the menu and in ebooks that supports extracting surrounding texts of words (i.e. epub, mobi but not pdf), the context of word use will be saved.
Tap on the ... button on each entry to view them.
Filter by books
Swipe north or use the menu to go to the book filtering view. Select books from which the words you want to review and tap on the ✅ button.
Word deletion
Use the menu to switch to quick deletion mode for easier deletion of multiple words. After finishing, go back to be menu and tap resume. You can also delete individual words from their more button on the right.
Data migration
The vocabulary database vocabulary_builder.sqlite3 is found in the settings folder under KOReader's root folder. You can copy and paste it to other devices for continued use.
Note that you should not use a database from a newer version of KOReader in an older version one, due to possibly incompatible data schema.