What is an atom?

An atom is the unit of memory Atomus actually reviews. It's a small front/back pair written inside one of your notes, and it's the thing that drops from your notch when it's due.

If you've used flashcard apps before, an atom is the same shape as a flashcard. The difference is where it lives and how it reaches you. There's no separate card editor or deck. You write a line of Markdown in a note, and that line is the atom.

The shape

Every atom has three pieces.

• Front: what you'll be asked. A question, a term, a prompt.
• Back: what you're trying to recall. The answer.
• Schedule: a stability and difficulty score that FSRS uses to decide when this atom comes back next.

That's the whole object. No tags, no decks, no metadata you have to maintain.

The six kinds of atom

A "front == back" pair is the simplest form, but not the only one. Atomus parses your Markdown and recognizes six shapes, all written in plain text.

Capital of France? == Paris

How does FSRS work? ==
  - tracks stability per atom
  - reschedules based on ratings
  - targets ~90% retention

Which is a hash map? ==
  (x) O(1) average lookup
  ( ) O(log n) sorted keys
  ( ) O(n) linear scan

Three laws of motion ==
  1. inertia
  2. F = ma
  3. equal and opposite

The {{mitochondria}} powers the cell.

- [ ] Finish biochem outline @2026-05-10
  Krebs cycle step 3 == isocitrate → α-ketoglutarate

Top to bottom: QA, multi-line, multiple choice, list answer, cloze, and deadline. The deadline isn't an atom itself. It's a task with atoms inside, and Atomus front-loads those atoms as the date gets closer.

You don't pick a type from a menu. Write the syntax, save, and Atomus chooses the review UI that matches.

Where atoms come from

Two paths, same result.

• You write front == back in any note. The line becomes an atom as soon as it's in the note.
• You write plain text and atomify a line with ⌥ A. If you've set up an AI provider, Atomus writes atoms for that line under it. Edit or delete any you don't want.

Either way, atoms live next to the note they came from. Open the note in your vault and you'll see the == pairs exactly as you wrote (or approved) them.

What atoms do

An atom exists for one purpose: to come back to you at the right moment. Once an atom is in your queue, FSRS schedules it. When it's due, a review appears from the notch. You rate it with one key. The schedule updates. The atom waits until next time.

Repeat this for a week and you have a small library of things you used to forget. Repeat it for a month and the shape of what you remember starts to change.

Atom vs. note

A note is the Markdown file you wrote. It's in your vault as plain text, readable in any editor.

An atom is a line (or a small block) inside that note. One note can hold zero, one, or many atoms. The text stays in the note; Atomus tracks its schedule and brings it back for review.

You read notes. You review atoms. Atomus keeps both in sync.