What Is Spaced Repetition?

Spaced repetition is a scientifically backed learning method that schedules reviews at increasing intervals. Rather than cramming, you review a card just before you're likely to forget it. This dramatically reduces study time while improving long-term retention, a principle supported by over a century of memory research.

The Leitner System

This tool uses a five-box Leitner system. New cards start in Box 1 (review daily). Answering correctly advances the card to the next box with a longer interval: 2 days, 4 days, 8 days, 16 days. Answering wrong returns the card to Box 1. Cards in Box 5 are considered mastered.

Importing Cards

You can import cards from any tab-separated (TSV) or comma-separated (CSV) file. Each row should have a front column, a back column, and an optional hint column. Most spreadsheet apps can export to CSV. You can also import a JSON file exported from this tool to restore a backup.

Your Data Stays in Your Browser

All decks are stored in your browser's localStorage. Nothing is sent to any server. Use the Export JSON button regularly to back up your decks. Clearing your browser data will erase them.

Optimal study session length

Research on spaced repetition supports sessions of 20–30 minutes with full attention rather than longer, distracted sessions. Typical effective review intervals for the Leitner system are 1, 3, 7, 14, and 30 days - reviewing a card just before you're likely to forget it locks it into long-term memory most efficiently. Cramming before a test can produce short-term recall but dramatically reduces retention after 48 hours.

Card writing best practices

One concept per card: if a card requires two sentences to answer, split it.
Cloze deletion: "The capital of France is ___" is more effective than "Q: What is the capital of France? A: Paris" for active recall.
Clear and specific questions: vague questions produce vague answers. "What does ATP stand for?" is better than "Tell me about ATP."
Use examples: including a worked example on the back of a formula card aids transfer to new problems.

Subject-specific tips

Languages: pair vocabulary cards with an example sentence to provide context; add audio pronunciation if your tool supports it.
Mathematics: put the formula on the front and a fully worked example on the back; add a separate card for each variation.
History: pair the date with the significance: "1789 -> French Revolution begins; causes include economic crisis and Estates-General dispute."

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