What does FSRS stand for?
FSRS stands for Free Spaced Repetition Scheduler — an open algorithm that schedules flashcard reviews based on predicted forgetting.
Guide
FSRS (Free Spaced Repetition Scheduler) is a modern algorithm that predicts when you will forget a flashcard and schedules the next review for that moment.
FSRS stands for Free Spaced Repetition Scheduler. It is an open spaced-repetition algorithm that models memory decay from review history — how often you see a card, how you grade each recall, and how long you retain it afterward. The goal matches classic spaced repetition: show each item again just before you forget it.
After each review you rate recall quality — for example again, hard, good, or easy. FSRS updates a memory state for that card and predicts the probability you would recall it at any future time. When that probability drops to your chosen target (many apps default around 90% desired retention), the card becomes due. Easy grades push the interval out; failures pull it in. Unlike fixed schedules (“1 day, 3 days, 7 days”), FSRS adapts per card and per learner.
SM-2 powered Anki for years with simple interval multipliers. FSRS improves on that family by training on large real-world review datasets (millions of reviews) to estimate forgetting curves more accurately. Learners often need fewer total reviews for the same retention — or stronger retention for the same study time. Modern Anki can optionally use FSRS; open-source libraries implement the same math in Python (py-fsrs) and Rust (fsrs-rs).
FSRS is documented in open research on spaced repetition — often cited as the “Free Spaced Repetition Scheduler” paper and related follow-ups. Searches for “free spaced repetition scheduler paper”, “FSRS python”, or “FSRS meaning” point to this same algorithm family — not a proprietary app-specific formula.
This guide covers the concept. See the feature page for how wordlet implements it in the app.
General answers about what is fsrs? — see the feature page for wordlet-specific setup.
FSRS stands for Free Spaced Repetition Scheduler — an open algorithm that schedules flashcard reviews based on predicted forgetting.
FSRS predicts when you are about to forget a card and sets the next review date. It powers schedulers in Anki (optional), py-fsrs, fsrs-rs, and apps built for long-term retention.
FSRS is one spaced-repetition algorithm — a specific way to compute intervals. Spaced repetition is the broader learning technique; FSRS is a modern implementation of it.
Fixed-interval apps repeat cards on preset timers (common in cram-focused tools). FSRS adapts each card’s schedule from your actual grades, which suits vocabulary you need to retain for months.