How the Leitner System Turns Flashcards Into Real Spaced Repetition
A flashcard maker lets you create decks of question-and-answer cards and study them, but this one does more than shuffle: it uses the Leitner system, a proven spaced-repetition method, so you spend your time on the cards you actually struggle with. Passive re-reading is one of the least effective ways to study; retrieval practice spaced out over time is one of the most effective. Students revising for exams, language learners building vocabulary, and anyone memorising facts get more out of the same study minutes with this approach. Everything is stored in your browser, so your decks stay private and work offline once loaded.
The Leitner system, devised by Sebastian Leitner in 1972, sorts cards into five boxes by how well you know them. Every new card starts in Box 1. When you review a card and get it right, it is promoted one box up, so it will be shown less often; when you get it wrong, it drops straight back to Box 1, so you see it every session until it sticks. The boxes correspond to review frequencies — roughly Box 1 every session, Box 2 every other session, Box 3 weekly, Box 4 fortnightly, and Box 5 monthly — which is the spacing that strengthens long-term memory. This tool implements that exact promote-on-correct, demote-to-Box-1 rule (capped at Box 5), and classifies your cards as new, learning (boxes 1 to 2), or mastered (boxes 4 to 5) so you can see progress.
Here is how a session flows. You create a deck and add cards with a front, a back, and an optional hint, or bulk-import them by pasting a list of term - definition lines or CSV. In study mode the tool shows a card's front; you try to recall the answer, flip to check, and then tap I knew it or I did not. If you knew a Box 2 card, it moves to Box 3 and you will see it less often; if you missed a Box 4 card, it falls to Box 1 and returns every session. Over several sessions the cards you know drift into the higher boxes and stop wasting your time, while the tricky ones stay in front of you. A card correct at Box 5 simply stays at Box 5, the mastered ceiling.
A medical student building a deck of drug names studies daily and watches the well-known ones settle into Box 5 while the confusable ones stay in Box 1 for extra drilling. A language learner imports a few hundred vocabulary pairs from a pasted list in one action rather than typing each card. A student before an exam prints the deck as a sheet to revise on paper away from a screen. Someone switching devices uses the JSON export to move a deck, or to back it up — which the tool encourages prominently, because browser storage can be cleared and losing a carefully built deck is a real setback.
The pitfall the Leitner system guards against is spending equal time on every card, including ones you already know cold; by pushing known cards into infrequent boxes it concentrates effort where it helps. The pitfall the tool itself warns about is data loss: decks live in your browser's local storage, which the browser can clear, so export important decks to JSON as a backup. Also remember spaced repetition rewards short, regular sessions over one long cram — the schedule only works if you come back. This is a study aid, not a guarantee, and it does not sync across devices without you moving the JSON yourself. Everything runs locally in your browser, so your decks are never uploaded anywhere.
