Osteon

Anki-style flashcards that live inside your Obsidian notes. Write a card as a line in a note, study it with one-key grading and FSRS scheduling, and keep notes and cards in one place on the computer and the phone.

What it does

• Your notes, one key away from any card: stuck on a card, press N and its note opens beside it
• Cards written in your notes, with a real back side
• Fast keyboard review with FSRS scheduling, undo, flags, bury and suspend
• One-by-one reveals for cards with several answers
• Image occlusion drawn on any picture in the vault
• Decks, presets and custom study
• Statistics and a review heatmap
• A card browser with a search language
• Deck import (.apkg), with review history
• An AI helper beside the card that explains it and answers questions, with your own key from any provider (optional)
• Medical-term hover
• Leeches, weak spots and timed sittings
• Works on iPhone and iPad through Obsidian mobile, with the same cards and history
• Card themes, a home-screen shortcut, game controllers and more, and an add-on API

Your notes, one key away

This is the reason Osteon exists. A flashcard holds one fact, and the note it came from holds the explanation. When a card is hard, press N and the note opens beside the card, scrolled to the line the card was written on. Read around it, then carry on reviewing.

• Pictures from the note: if a card has no picture of its own, its back shows the figures from the same section of the note.
• Related notes: the back lists notes whose title the card mentions. Click one, or press N on an imported card to open the best match.
• Term hover: hover a term on the back to see the first paragraph and pictures of your own note about it.
• From the note back to its cards: Osteon: Study this note's cards (also in the note's menu) builds a deck from one note, and note:"..." works in Browse and filtered decks.
• Edit in place: E edits the card without leaving the review, and the change is written to the note.
• Linked decks: a vault can ship a table that ties each card of an imported deck to the note about it, so a shared deck opens the right note too.

Link any note to any card. If a card keeps sending you back to the same note, tie them together: in a review, open the ⋯ menu and choose Link a note to this card. From then on N opens that note from that card, and it leads the Related row. It works on every card, including cards from an imported deck, and the link follows the note if you rename or move it. Unlink from the same menu.

The picker first offers the notes that look related to the card. Type to search: titles, aliases and headings, with the words in any order. If you have the Omnisearch plugin, the picker uses it and searches inside your notes too.

Imported decks work differently. A card from an imported deck was not written in one of your notes, so there is no source note for N to open. Instead N opens a note you linked to the card, or else a note of yours that the card names. If there is none, it tells you so and opens the deck's own card file. The AI helper can also point you to the right note: it lists the notes of yours it judges relevant under each explanation. The cards you write in your own notes always open the exact line.

Cards written in your notes

Add #flashcards to a note (or list its folder in settings). Then write:

The most commonly torn rotator cuff tendon is ==supraspinatus==.
Tested with the empty can (Jobe) test.

Which nerve supplies supraspinatus and infraspinatus? :: Suprascapular nerve

The rotator cuff muscles are {{c1::supraspinatus}}, {{c1::infraspinatus}}, {{c1::teres minor}} and {{c1::subscapularis}}.
![[rotator-cuff.png]]

The first line is the front. The lines under it are the back, shown only after you answer, so the explanation never has to be squeezed into the blank. Pictures, links, lists and math work on either side. Three styles are understood: ==highlight== clozes, {{c1::answer::hint}} clozes, and Question :: Answer (::: makes a reversed pair too). A deck is the note's folder, or a #flashcards/deck/subdeck tag.

The full syntax is in docs/claude-code-skill/SKILL.md, which also works as a Claude Code skill for writing cards. Add card (A) writes a card into a note for you, and Osteon: Migrate from Spaced Repetition… converts cards from the Spaced Repetition plugin and keeps their schedules.

Review

Open the deck list from the ribbon icon or Osteon: Open decks. Space shows the answer, then 1 Again · 2 Hard · 3 Good · 4 Easy.

• D decks, B browse, A add card, T stats
• U or ⌘Z undo, E edit the card in place, N open its note
• * mark, ⌘1–7 flags, - bury, @ suspend, ⌘⇧D set due date
• I card info, O deck options

Every key can be changed in settings. Scheduling is FSRS, and a deck's parameters can be optimised from your own history.

A game controller works too.

iPhone and iPad

Osteon runs inside Obsidian mobile, so there is no second app and nothing to export. The same notes, cards and review history are on the phone as soon as your vault syncs (iCloud or Obsidian Sync).

• Tap the right third of the screen for Good and the left third for Again, or use the buttons.
• Shake to undo.
• Tap a term for its definition, tap a figure to zoom, and open the card's note the same way.
• Each device keeps its own review log, so studying on the phone and the computer never conflicts.
• Osteon warns you if iCloud has offloaded your pictures from the phone.

One-by-one reveals

A card that asks for two or more answers hides each one behind a 🦴 and reveals them one at a time, so a list is recalled item by item instead of all at once. N or Space reveals the next, a click reveals that one, and comma reveals all. The bone button above a card switches it on or off for that card.

Image occlusion

Put a picture on a line of its own, right-click the line and choose Create image occlusion. Draw rectangles, ellipses or polygons over the labels. Each box, or group of boxes, becomes a card. Hide all, guess one suits labelled diagrams and Hide one, guess one suits X-rays.

In review, tap the figure to zoom and press T to uncover every box. In the note, the figure still shows, with an Edit occlusion button. Renaming the image updates the figure.

Decks and options

The gear next to a deck opens its options: presets shared between decks, new and review limits, learning steps, leech threshold, display order, burying, timers and FSRS parameters. Decks can be renamed or hidden from the same menu.

• Custom Study (C on a deck): raise today's limits, review forgotten cards, review ahead, preview new cards, or study by state or tag.
• Filtered decks (F): a saved search with a limit and order, with Rebuild and Empty.
• Timed sittings: 5, 10, 15 or 20 minutes from a deck's overview.
• Pacing (optional): hold back new cards while many are still in learning, and rest a card after several misses in one day.

Statistics

Stats has graphs for Today, Future Due, Calendar, Reviews, Card Counts, Intervals, Stability, Difficulty, Retrievability, Hourly, Answer Buttons, Added and True Retention. The year heatmap and streaks also sit under the deck list; click a day to browse its cards.

Browse

Browse takes searches such as deck:Anatomy is:due, tag:high-yield, flag:1, prop:ivl>30 or rated:7, plus is:onebyone, front:word and A or B. Select cards to suspend, flag, reschedule or switch them to one-by-one in bulk.

Finding what you keep missing

• Leeches: cards that reached the deck's leech threshold, each with Rewrite, Split into one-by-one, Try again or Drop.
• Weak spots: miss rate by topic and the most-missed cards for today, 7 or 30 days, with a practice run that isn't recorded.
• Find cards to rewrite: lists overstuffed cards whose explanation sits inside the blank.
• Exam results: with a vault that ships an *.exammap.json table, enter the questions you missed on a practice exam and study the notes behind them.

Medical-term hover

After you reveal a card, medical terms are underlined. Hover on the computer, or tap on the phone, to see a short definition without leaving the card.

Definitions come from, in order:

1. Your own notes: a note whose title or alias matches the term. The popup shows its first paragraph and pictures.
2. Your list: Flashcards/glossary/My terms.md (command Open My terms).
3. MeSH: the National Library of Medicine's vocabulary. Press Download in settings, once per device.
4. AI, if you turn it on.

Everyday words aren't underlined. Underlines on the front of a card are off by default, because a definition can give away the answer.

AI helpers (optional)

Pick a provider in settings, add your own API key and the model's name (filled in for you with Claude and Gemini), then turn on Use AI. Anthropic (Claude), OpenAI, Google Gemini and OpenRouter are built in, and Other takes any service that accepts OpenAI-style requests, including a model running on your own computer (Ollama, LM Studio).

AI helper panel. Press H during a review, or the sparkle button above the card, and a panel opens beside the card. Explain this card tells you why the answer is what it is and gives a memory hook. Then ask anything else about the card in the box below.

• Its own explanation. The helper answers from its own knowledge, not by repeating your note.
• It checks your note. Notes can be wrong. The helper reads the part of your note the card came from, and if it conflicts with the facts it says so under Check your note.
• Links to your notes. The helper is shown the titles of your notes that might fit and picks the ones that are truly about the card. They are listed under each answer, and a click opens one beside the card.
• No spoilers, no surprises. It stays quiet until the answer is showing, follows you from card to card, and sends nothing until you press a button.

Also:

• Hard terms: finds terms the dictionaries miss, like eponyms, abbreviations and classifications, and writes one- or two-sentence definitions for the term hover. They are saved in the vault, so each card is looked at once and the definitions work offline on the phone.
• Suggest split: proposes a short front plus a back for an overstuffed card. Nothing is written until you press Accept.

AI answers can be wrong, including about medicine. Treat them as a study aid and check anything you will rely on; the panel says so too.

For hard terms, new cards are looked at in small batches in the background (this can be turned off). Bigger runs always ask first.

Importing decks (.apkg)

Run Osteon: Import deck (.apkg)…, or press Import deck under the deck list, and pick the file. It works for shared .apkg decks and for your own exports (tick "Include scheduling information" when exporting to keep your history).

A preview shows what's inside. The deck is then written into the vault as notes, one per sub-deck, with its pictures beside them, and old image-occlusion notes become real occlusion figures. If the export included review history, cards keep their exact memory state.

Importing a newer version of the same deck only adds the new notes, or, with Update cards imported before, rewrites the old ones and keeps their history (never cards you edited in Obsidian). Very large decks with gigabytes of media are best imported on a computer.

Osteon ships no decks. Bring your own.

More

• Card themes: several looks for the card, a background picture, and a font size.
• Home-screen shortcut: point an Obsidian widget or bookmark at a shortcut note to open your decks in one tap, or use the links obsidian://osteon and obsidian://osteon?study.
• Game controller: grade, undo and reveal from a controller, with remappable buttons.
• Auto advance and timers: show the answer and move on after a set time.
• Card info: a card's full review history and memory state (I).
• Syncs cleanly: each device writes its own review log, so iCloud or Obsidian Sync never has to merge two devices' answers, and card IDs are ordinary block IDs in your notes.
• Card callouts: keep cards in a > [!card] callout if you prefer them boxed.

For add-on authors

app.plugins.getPlugin("osteon").api provides:

• registerReviewDecorator(fn)
• on("cardShown" | "answerShown" | "answer" | "sessionEnd", cb)
• cards(search), cardState(key), history(key)
• suspend, unsuspend, bury, reset, flag and setDue

See src/plugin/api.ts.

Installing

In Obsidian, go to Settings → Community plugins → Browse, search for Osteon, then install and enable it. If your vault syncs its settings folder (iCloud or Obsidian Sync), enable it on the phone too.

To install by hand, download main.js, manifest.json and styles.css from the latest release into <your vault>/.obsidian/plugins/osteon/.

Recommended: Settings → Files and links → Excluded files, then add Flashcards/reviews so the review logs stay out of search and the graph.

Review history lives in Flashcards/reviews/<device>/<month>.md. Each device writes only its own files, so a sync service never has to merge them.

Network use, files and privacy

Osteon has no telemetry, no ads and no account. It contacts the internet in two cases only, both started by you:

• MeSH download (nlmpubs.nlm.nih.gov): when you press Download for the medical-term hover, it fetches the National Library of Medicine's public MeSH vocabulary. Nothing is sent.
• AI helpers: only if you add your own API key and turn on Use AI. The text of the cards being looked at, and for a question in the helper panel the part of the note around that card and the titles of related notes, is sent to the provider you picked (Anthropic, OpenAI, Google, OpenRouter, or the server address you typed) to write definitions, explanations or rewrite suggestions. Usage is billed by that provider.

Files outside the vault are read in two cases, both started by you: the .apkg file you pick to import, and (desktop only) Copy deck pictures into the vault, which reads the media folder of the flashcard app profile you choose so that imported cards get their pictures.

Your API key is kept in Obsidian's secret storage on that device. The optional Sync the key switch (off by default) also writes it, in plain text, to api-key.json in the plugin's folder so your other devices pick it up. Leave it off if your vault is shared or public.

Development

npm install
npm test        # parser, scheduler/replay, queue, and data-layer integration tests
npm run build   # typecheck + bundle to main.js

Tests use a throwaway sample vault in test/fixtures/vault/ and an in-memory mock of the Obsidian API (test/mocks/obsidian.ts).

Credits and license

MIT licensed (see LICENSE). Scheduling uses the open FSRS algorithm through ts-fsrs (MIT). It also bundles sql.js, fflate, fzstd, zod and the Anthropic SDK (all MIT), and a common-English word list from google-10000-english. Osteon is an independent project, not affiliated with or endorsed by Anki or its developers. It ships no decks.

The anatomy plates in the screenshots are from Gray's Anatomy (1918), public domain.