What is FSRS?
FSRS is a spaced repetition algorithm: it estimates how likely you are to remember each item and schedules the next review just before you would forget it. For each card it tracks three numbers: difficulty, stability (how long the memory lasts) and retrievability (the chance you recall it right now). You choose a target retention, for example 90%, and the scheduler picks the interval that meets it.
What does FSRS stand for?
Free Spaced Repetition Scheduler, an open-source scheduling algorithm by Jarrett Ye and the open-spaced-repetition community.
How is FSRS different from SM-2?
SM-2, the 1987 algorithm behind classic Anki, multiplies the interval by a fixed ease factor. FSRS models each card's difficulty, stability and retrievability and picks the interval that hits a target retention, which usually means fewer reviews for the same recall.
Is FSRS available in Anki?
Yes. Anki added FSRS as an optional scheduler in version 23.10.
Does fudami use FSRS?
Yes. fudami schedules every kana, kanji and word with FSRS. The app is still in development; join the waitlist to hear when it opens.