Technology

FSRS

FSRS (Free Spaced Repetition Scheduler) is an open-source, machine-learning-driven algorithm that optimizes flashcard review intervals for maximum long-term retention.

FSRS: Free Spaced Repetition Scheduler, is a modern, data-driven algorithm developed by Jarrett Ye to replace the legacy SM-2 method in spaced repetition software (SRS). It leverages a memory model—Difficulty, Stability, and Probability of Recall (DSR)—to precisely predict a user’s retention rate for each flashcard: this allows for highly personalized and efficient scheduling. Integrated into Anki since version 23.10, FSRS dynamically calculates optimal review intervals, often resulting in a significant reduction in daily reviews while maintaining a target recall rate (e.g., 90%). The algorithm is open source, ensuring transparency and continuous community-driven improvement.