The FSRS flashcard app for iPhone

Azri schedules every card with spaced repetition (FSRS), the open-source algorithm Anki also offers. It’s free, it works from your first review, and you can tune it when you want to

See how it works FSRS vs SM-2
Free on iPhone & iPad FSRS-5 on iPhone, iPad and the web Nothing to set up

What spaced repetition (FSRS) is

Spaced repetition shows you a card again just before you’d forget it. FSRS is the algorithm that works out when that is.

You forget new things fast, then more slowly each time you manage to recall them. Spaced repetition builds on that: every successful review pushes the next one further out, so your time goes to the cards you’re about to lose, not the ones you already know.

FSRS (Free Spaced Repetition Scheduler) is an open-source algorithm from the open-spaced-repetition project. It tracks three things for each card: difficulty (how hard the card is for you), stability (how long the memory lasts) and retrievability (your chance of recalling it right now). After every review it updates them, predicts how fast you’ll forget, and schedules the card for the day your chance of remembering drops to your target.

Anki added FSRS as an option in version 23.10. Its default parameters come from the review histories of about 20,000 Anki users, so it works well before it knows anything about you.

How Azri schedules your reviews

You never see a formula. You rate each card, and Azri decides when it comes back.

  1. Rate the card

    After you see the answer, tap Again, Hard, Good or Easy. Each button shows when the card will come back, so you know what you’re choosing.

  2. FSRS updates it

    Your rating changes the card’s stability and difficulty. A card you knew cold waits longer. A card you missed comes back soon.

  3. New cards take short steps first

    With short-term optimization on, a card you’re still learning comes back within minutes in the same session before it moves out to days.

  4. It returns when you’re likely to forget

    Azri schedules the card for the day your predicted recall drops to your target retention, 90% by default. Fuzz moves due dates slightly, so cards you learned together don’t all land on the same day.

Azri review screen showing the answer Salut, with Again under 1 minute, Hard 4 minutes, Good 9 minutes and Easy 3 days
Each button shows the next interval before you tap it.

Presets and target retention

Most people never change anything. If you want to, go to Profile → Spaced repetition, or tap the settings button during a review.

Azri’s spaced repetition presets on iPhone, iPad and the web app. Fuzz and short-term optimization are on in every named preset.
Preset Target retention Longest gap
Default A balance of reviews and memory. Start here. 90% 1 year
Aggressive An exam coming up. More reviews, fewer slips. 95% 90 days
Relaxed Big decks or busy weeks. Fewer reviews, a few more misses. 85% 1 year
Custom Your own target, with switches for fuzz and short-term optimization. 80–99% 30 days to 1 year

Target retention is your chance of remembering a card when it comes up. Raise it and cards come back sooner, so you review more. Anki’s manual notes that the workload rises quickly above 90% and can become overwhelming above 97% (Anki manual, desired retention).

Longest gap is the furthest out a card can be scheduled, however well you know it.

With Pro, your preset syncs to your other devices and the web app, which uses the same presets.

Azri spaced repetition settings with Default, Aggressive, Relaxed and Custom presets. Custom is selected, with a 98% target retention, a 30-day maximum interval, fuzz off and short-term optimization on
The Custom preset, set to 98% retention with fuzz off.

Why it beats fixed intervals

Plenty of study plans space reviews on a fixed schedule, like 1, 3, 7, 14 and 30 days, or Leitner boxes. FSRS spaces each card on its own.

Fixed intervals

  • Every card gets the same gaps, easy or hard.
  • Easy cards come back too often. Hard ones don’t come back often enough.
  • A card you keep getting wrong restarts on the same track as every other card.
  • No way to trade fewer reviews for slightly lower recall, or the other way round.

Spaced repetition (FSRS)

  • Each card’s gap depends on how you’ve answered it.
  • Easy cards drift out to months. Hard cards stay close.
  • Late reviews count: FSRS uses the real time since you last saw the card.
  • One number, target retention, sets the trade-off between reviews and recall.

How FSRS compares with SM-2

Good to know before you rely on it

Azri keeps spaced repetition simple. Here’s what that leaves out.

Azri runs FSRS-5

Newer versions, FSRS-6 and FSRS-7, have been published since. In the open benchmark, the step from FSRS-5 to FSRS-6 is much smaller than the step from SM-2 to FSRS-5.

No personal optimizer

Anki can fit FSRS’s parameters to your own review history. Azri uses FSRS’s default parameters for everyone. They’re a strong start, and each card still adapts to your ratings, but they aren’t tuned to you.

Gaps top out at one year

The named presets cap the time between reviews at one year (90 days in Aggressive), and Custom lets you pick from 30 days to one year. Anki’s default cap is 100 years, so cards you know very well come back more often in Azri.

Anki history doesn’t come with you

Decks you import from Anki start as new cards, and FSRS learns them from your first review in Azri. The import guide covers what comes over.

Questions about spaced repetition in Azri

Is spaced repetition (FSRS) free in Azri?
Yes. On the free plan every review is scheduled with FSRS, and the presets and custom settings are free too. Pro adds extras like cloud sync and the web app, not a better scheduler.
Which version of FSRS does Azri use?
FSRS-5, on iPhone, iPad and the web app. The iPhone app uses the open-source swift-fsrs library and the web app uses ts-fsrs. Both come from the open-spaced-repetition project and use the same presets.
Do I need to change any settings?
No. The Default preset aims for 90% retention, the usual starting point. Change it only if you want fewer reviews (Relaxed) or more (Aggressive).
What target retention should I pick?
Start at 90%. Raise it before an exam if you have time for more reviews. Anki’s manual notes that the workload rises quickly above 90% and can become overwhelming above 97%.
What happens if I skip a few days?
Nothing is lost. Overdue cards wait in your queue, and FSRS uses the real time since your last review when it schedules the next one.
Can I bring my Anki review history?
No. Cards you import from Anki start as new cards, and FSRS learns them from your first review in Azri. The import guide explains what comes over.

Let FSRS do the remembering.

Azri is free on iPhone and iPad. Add a few cards, do one review, and spaced repetition (FSRS) takes it from there.

Download Azri on the App Store Read FSRS vs SM-2