Lumen - Flashcards App

Lumen is a flashcard app for people who want spaced repetition to work properly and want their data to stay on their phone.

SCHEDULING THAT MAKES SENSE

Cards are scheduled with FSRS-6, which models memory as difficulty, stability, and retrievability instead of a fixed ladder of intervals. Every rating button previews the interval it would give you before you tap it, so you can see what Again, Hard, Good, and Easy actually cost. All 21 FSRS weights and your desired retention are editable, with bounds checking so you cannot save a set that breaks scheduling. You can undo a review, reset a card or a whole deck, and reschedule individual cards.

BRING THE DECKS YOU ALREADY HAVE

Import from Anki .apkg files, Anki JSON, CSV and TSV, Markdown, and Lumen's own ZIP backups. Anki's rendered HTML is stripped on the way in, so you get clean card faces instead of stray markup. Imports are idempotent, so re-importing a deck or overlapping HSK levels will not duplicate anything. Export your decks whenever you want them elsewhere.

BUILT FOR CHINESE, USEFUL FOR EVERYTHING

The HSK importer reads the complete-hsk-vocabulary dataset and keeps every written form, numeric pinyin, radical, and frequency rank. Chinese notes render tone-colored pinyin alongside simplified and traditional forms, meanings, part of speech, HSK level, and classifiers. Each word can generate both recognition and production cards. Text-to-speech reads cards aloud, with the spoken language set per deck.

For other subjects there are Basic, Basic and Reversed, and Cloze note types, Markdown formatting on card faces, nested decks at any depth, image and audio attachments, and full-text search across your collection.

YOUR CARDS STAY ON YOUR DEVICE

Lumen works offline and has no accounts. Your decks, notes, review history, and media live in a database on your phone, and nothing syncs to a server. Lumen reports anonymous usage and crash data so bugs get fixed, and that reporting excludes deck names, tag names, note contents, search queries, and file paths. Settings has a reset that erases everything locally.

KEEPING THE HABIT

A daily goal, streaks, XP, and achievements track consistency. The stats screen shows review counts, retention, daily accuracy, rating distribution, how card difficulty is trending, and a heatmap of your study activity. You can share a streak or heatmap card as an image without sharing the cards themselves.

Lumen has no ads and nothing to unlock by paying.