Spaced repetition, without making a single flashcard.
Axo is a spaced repetition app that writes the cards for you. Every idea you learn gets a memory score and a next-review date, and Keep Sharp asks you about it right before you would forget it.
By the Axo team · Last updated November 9, 2026
How Keep Sharp works.
Memory fades on a curve. A review just before you would forget resets the curve with a flatter slope. Keep Sharp times each review for that moment.
Every question maps to one idea.
Axo calls it a concept: one testable statement. It is the unit of spaced repetition, and you never write one yourself.
Each idea gets a score and a date.
Answer well and the next review moves further out. Miss it and it comes back sooner.
Keep Sharp pulls what is due today.
One short session, across all your Paths. No deck to pick and no pile to manage.
It mixes topics on purpose.
Ideas from different units and Paths arrive interleaved. That feels harder and works better.
The question changes.
An idea that comes back is asked another way than you first met it, and on review you type the answer from memory.
A model, not a measurement. Each review resets the curve and flattens the next one.
- Read once
- With Keep Sharp
2 of 4 reviews, on days 1, 3
Table view
| Day | Read once | With Keep Sharp |
|---|---|---|
| 0 | 100% | 100% |
| 1 | 66% | 100% |
| 3 | 29% | 100% |
| 7 | 5% | 73% |
| 14 | 0% | 42% |
| 21 | 0% | 24% |
| 30 | 0% | 12% |
The research under it.
| What | Number | Note |
|---|---|---|
| The forgetting curve | Ebbinghaus, 1885 | Memory fades fast at first, then slower. The shape has held up since. |
| Retrieval practice | Roediger and Karpicke, 2006 | Pulling an answer out of memory strengthens it far more than reading it again. |
| Desirable difficulty | Bjork | Recall that is a little harder leads to memory that lasts longer. |
| Interleaving | Mixed beats blocked | Mixing related ideas teaches you to tell them apart. |
| Keep Sharp on Free | 3 Paths | Plus and Pro run Keep Sharp on every Path. |
| Flashcards you write | 0 | The cards come from the Bites you finished. |
What it will not do.
Each of these is a thing we left out on purpose, because the research does not support it.
- No cramming mode
- Keep Sharp brings an idea back just before you would forget it, not the night before a test.
- No review without a question
- There is no screen that shows you the text again and calls it review. Every card asks.
- No learning-styles quiz
- There is no evidence that matching a lesson to a learning style helps.
Questions people ask.
What is spaced repetition?
It is a way to study in which each review comes later than the one before, timed for just before you would forget. It is the best-supported method in the science of learning for keeping what you learn.
What is the forgetting curve?
It is the curve Hermann Ebbinghaus drew in 1885 that shows how memory fades: fast at first, then slower. A well-timed review resets the curve and flattens it.
Do I need to make flashcards?
No. Axo makes a card for every idea in the Bites you finish. Keep Sharp shows you the cards that are due today.
How is Keep Sharp different from a flashcard app?
You do not build or manage a deck. The cards come from a course you took, the question is asked a new way each time, and on review you type the answer from memory.