Tap a rating the way you would in Anki and watch the schedule react — interval, stability and difficulty, review by review. Everything runs in your browser. No signup, nothing stored.
| # | Rating | Interval | Due (day) | Stability | Diff | |
|---|---|---|---|---|---|---|
| No reviews yet — tap a rating above. | ||||||
One lapse is expensive. Hit Again after a long interval and stability collapses — the algorithm has to rebuild it from near zero, so a single forgotten review can undo months of spacing. Try Good ×5, then a lapse and compare the interval before and after.
Desired retention drives your workload. Dropping from 90% to 85% stretches every interval noticeably, meaning fewer reviews per day for the same deck — at the cost of forgetting more often. Slide it and watch the table recompute.
Intervals are capped at 36500 days, the same maximum interval Anki ships with by default.
This is FSRS-4.5 with the default weights, the same algorithm built into modern Anki. It's an independent implementation, so treat it as a teaching tool rather than a byte-exact replica of your scheduler.
The same scheduler is available as a hosted JSON API — POST a card state and a rating, get the next due date back. Free tier, no signup required.
curl -X POST https://smeltworks.com/studysched/v1/fsrs/review \
-d '{"rating":3}'