ji4.de

ji4.de is a spaced repetition system (SRS) for learning Chinese. This means that it tracks the words you study, and tries to show you words at the intervals that make you learn as fast as possible—not so long that you forget, but not so short that you waste effort on unnecessary reviews. Spaced repetition is widely considered to be the most efficient way to memorize vocabulary, or anything else.

Spaced repetition was popularized by SuperMemo. It's implemented by many flashcard applications, most notably Anki. ji4.de is distinctive for its:

Sentence study, word repetition

It's easier to learn from words in context than from definitions of words alone. ji4.de selects from a database of over a million example sentences, drawn from print news, popular websites, transcribed speech, and other public sources. It finds sentences that contain the words you need to review, by reading or listening.

After you read a sentence, mark the words you didn't remember. ji4.de then updates the review schedule, later for the words you remembered and sooner for any words you forgot.

Flexible scheduling of reviews

The spaced repetition algorithm calculates the optimal moment to review each word, but you may not be free to study then. ji4.de tries to make most efficient use of your time, regardless of how much or little you're able to study in a given day.

Not much changes if you review a word that you last reviewed a year ago a day or late early; but if you last reviewed a word yesterday, then reviewing it a day early is redundant, and reviewing it a day late risks forgetting. We model this by prioritizing words by relative dueness ("late by x% of review interval"), not absolute ("late by x days").

Open vocab import and export

If you're already using a different SRS, then you can import a word list (including scheduling), in order to continue your reviews without loss of efficiency. If not, then you can take a placement test. Then add specific words to study, or ji4.de can suggest the most frequently-used words that you don't already know.

ji4.de can also export your current progress in a format that you can import into other tools, or view and manipulate in most spreadsheet applications.

Detailed settings and analytics

The algorithms that determine how words are spaced and what sentences are chosen are highly customizable. You can evaluate your performance using analytics, and tune the system for the behavior you find most pleasant and effective.

I built this to help myself learn Chinese, and I believe it's useful for upper beginning (HSK 2-3) to advanced students. For now, I'm running it as a totally free service, for fun and to gather data that will help me tune the algorithms to learn more efficiently. In future, I may add paid features (better corpora, etc.) or run advertisements. Basic spaced repetition will always be free.

Take care that:

So with those caveats,

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