FSRS-light explained

A learning system needs to decide when each page should come back for review.

Reviewing too often wastes time. Reviewing too late increases the chance of forgetting. Yuhimo uses FSRS-light to adjust the next review date based on how well you remembered the page.

FSRS-light is Yuhimo’s lightweight scheduling model.

It is inspired by the idea that memory becomes more or less stable over time, and that reviews should be scheduled based on how well you remembered the material. It is not the full official FSRS implementation used by Anki.

For each learning page, Yuhimo tracks a small learning state instead of creating separate flashcards.

• Stability
• Difficulty
• Retrievability
• Next review date
• Review history

Stability is Yuhimo’s estimate of how strongly the page is held in memory.

Higher stability usually means a longer interval before the next review. Lower stability means the page should come back sooner.

For example, a page with low stability may return soon. A page with high stability may be scheduled further into the future.

New learning pages begin in a short acquisition phase with low initial stability. After successful reviews, stability can grow and intervals can become longer.

Before graduation, pages use short fixed steps in the learning phase. FSRS-light drives scheduling mainly after a page enters review. See Learning phase vs review phase.

Difficulty represents how hard the material feels for you.

A difficult page should not grow its review interval too aggressively. An easier page can move further into the future faster.

Difficulty is not a global score. It belongs to a specific learning page and changes over time based on your ratings.

New learning pages start with a default difficulty value that adjusts as you review. Harder ratings tend to increase difficulty; easier successful ratings can lower it over time.

FSRS-light keeps scheduling values within practical ranges. These are guardrails in the model, not settings you manage in the UI.

• Stability is kept roughly between 0.5 and 365 days
• Difficulty is kept between 1 and 10
• After a review-phase grade, the next interval is kept roughly between 1 and 180 days

You still interact with due dates and your own grades. If a page feels due sooner or later than you expect, your rating and timing matter more than any single internal number.

To see stability and difficulty after reviews, use Learning statistics.

Retrievability is an estimate of how likely you are to recall the page at a given moment.

As time passes after a review, retrievability goes down. If a page has not been reviewed for a long time, Yuhimo treats it as more likely to be forgotten.

Retrievability helps Yuhimo reason about review timing, especially when a page is reviewed early or late.

After each review, your rating updates the learning state of the page.

• Again means the material was mostly forgotten, so the page should return sooner.
• Hard means the material was remembered with effort, so the schedule stays careful.
• Good means the material was remembered well enough, so the interval can grow.
• Easy means recall was clear, so the interval can grow more.

These ratings are scheduling signals, not exam scores. They come from self-assessment.

If you review a page earlier than planned, Yuhimo limits how much the interval can grow.

This prevents the schedule from being inflated by reviewing a page too soon. Early reviews can still be useful, but they do not count the same as reviews done closer to the planned date.

See Early and late reviews for more detail.

If a page is overdue and you still remember it, Yuhimo may increase stability more than it would for an on-time review.

The reason is simple: if you remembered the material even after a longer delay, the page may be more stable than the previous schedule estimated.

This does not apply the same way when you choose Again, because Again means the material was mostly forgotten.

FSRS-light applies after a page graduates to review. In review, each page can receive only one grade per calendar day.

During the initial learning phase, short step intervals control when a page returns. That phase uses different rules before long-term FSRS-light scheduling takes over.

The full rule is explained in One grade per day.

FSRS-light does not decide whether your answer was correct.

It does not know which parts of a long page matter most to you. It also does not replace honest self-assessment.

• Automatically check correctness
• Understand the full meaning of your page
• Decide which facts are important
• Replace honest self-assessment
• Guarantee perfect memory

The scheduler only works with the signal you give it after review.

Yuhimo does not ask you to manage retrievability, stability, or difficulty directly.

In practice you see whether a learning page is due and what its next review date is after you grade. Retrievability is an internal estimate that helps adjust scheduling — especially for early or late reviews — not a number you need to track.

For a fuller explanation of retrievability and due dates, see Retrievability.

You review a page called "React useMemo".

At first, the page has moderate stability and difficulty.

If you choose Again, Yuhimo schedules it sooner. If you choose Good, the next interval grows moderately. If you choose Easy, the next interval grows more.

If you review it late and still choose Good or Easy, Yuhimo may treat the page as more stable than expected.

FSRS-light is the scheduling layer behind Yuhimo learning pages.

It uses your review rating, stability, difficulty, and timing to decide when a page should come back. The model stays lightweight because Yuhimo is built around flexible pages and honest self-assessment, not automatic testing.

Is FSRS-light the same as Anki FSRS?

No. Yuhimo uses a lightweight custom scheduler inspired by FSRS-style ideas. It is not the full Anki FSRS implementation.

Does FSRS-light grade my answers?

No. You grade your own recall. FSRS-light only uses your rating to schedule the next review.

What is stability?

Stability is Yuhimo’s estimate of how strongly a page is held in memory. Higher stability usually means a longer interval.

What is difficulty?

Difficulty estimates how hard the page feels for you. Higher difficulty keeps interval growth more conservative.

Why does reviewing early give less progress?

Because the page has not gone through enough of the planned interval yet. Yuhimo limits the scheduling reward to avoid inflated intervals.

Why can an overdue review increase the interval more?

If you still remember an overdue page, it may be more stable than the previous schedule estimated.