# hashcards
[](https://github.com/eudoxia0/hashcards/actions/workflows/test.yaml)
[](https://github.com/eudoxia0/hashcards/actions/workflows/release.yaml)
[](https://codecov.io/gh/eudoxia0/hashcards)
[](https://deps.rs/repo/github/eudoxia0/hashcards)
A plain text-based spaced repetition system. Features:
- **Plain Text:** all your flashcards are stored as plain text files, so you can
operate on them with standard tools, write with your editor of choice, and
track changes in a VCS.
- **Content Addressable:** cards are identified by the hash of their text. This
means a card's progress is reset when the card is edited.
- **Low Friction:** you create flashcards by typing into a text file, using a
lightweight notation to denote flashcard sides and cloze deletions.
- **Simple:** the only card types are front-back and cloze cards. More complex
workflows (e.g.: Anki-style note types, card templates, automation) be can
implemented using a Makefile and some scripts.
- **Efficient:** uses [FSRS] for scheduling reviews, maximizing learning while
minimizing time spent reviewing.
Announcement blog post: [Hashcards: A Plain-Text Spaced Repetition System][blog].
## Example
The following Markdown file is a valid hashcards deck:
```
Q: How many neurons are there in the human brain?
A: ~80 billion.
C: An [agonist] is a ligand that binds to a receptor and [activates it].
Q: How many synapses are there in a human brain?
A: ~100 trillion
C: In the nervous system, [chemical] communication happens [between] neurons.
```
For a larger example, see [my personal flashcards repo][fc].
## Installation
You can download a binary from the the [releases](https://github.com/eudoxia0/hashcards/releases) page.
If you have [cargo] installed, you can run:
```
$ cargo install hashcards
```
On Arch Linux, you can install it from [AUR](https://aur.archlinux.org/packages/hashcards-bin).
## Building
You need [cargo] installed. You can get it through [rustup]. Then:
```
$ git clone https://github.com/eudoxia0/hashcards.git
$ cd hashcards
$ make
$ sudo make install
```
To drill flashcards in a directory, run:
```
$ hashcards drill $DIRNAME
```
## Tutorial
Create a directory for your flashcards, and add a Markdown file with some cards:
```bash
$ mkdir cards
$ cd cards
$ cat > Geography.md << 'EOF'
Q: What is Coulomb's constant?
A: The proportionality constant of the electric force.
Q: What is an object with zero net charge called?
A: Neutral.
EOF
```
A Markdown file is called a "deck", and the name of the file, sans extension, is
the name of the deck. This will be shown on top of the flashcard during reviews,
this saves you from having to specify the context in each of the flashcards.
Start drilling:
```bash
$ hashcards drill
```
This opens a web interface at `http://localhost:8000` where you can review your
cards. The interface is simple: you read the question, mentally recall the
answer, and click reveal (or press space). Then you grade yourself on how you
did, with one of four choices:
1. Forgot (shortcut: `1`)
2. Hard (shortcut: `2`)
3. Good (shortcut: `3`)
4. Easy (shortcut: `4`)
Be honest. If you got the answer almost right, press "Forgot". If you mis-grade
something, you can undo (shortcut: `u`). The session ends when every card has
been graded "Good" or higher. You can end the session prematurely by clicking
"End", this will save your changes.
To learn how to write good flashcards, read [Effective Spaced Repetition][esr].
## Commands
This section documents the hashcards command line interface.
### `drill`
Start a drilling session.
```bash
$ hashcards drill [DIRECTORY]
```
Note: your progress is not saved until the session ends, either when you run out
of cards, or when you click "End".
Options:
- `--card-limit=<N>`: Limit the session to at most N cards.
- `--new-card-limit=<N>`: Limit the number of new cards in the session.
- `--port=<PORT>`: Use a specific port (default: 8000).
- `--from-deck=<NAME>`: Only drill cards from a deck with the given name.
- `--open-browser=<true|false>`: Whether or not to open the browser after the
server starts (default: true).
### `stats`
Print collection statistics to standard output.
```bash
$ hashcards stats [DIRECTORY]
```
Options:
- `--format=<FORMAT>`: Output format (`html` or `json`)
At present, only JSON output is supported.
### `check`
Check the integrity of a collection.
```bash
$ hashcards check [DIRECTORY]
```
### `orphans`
Manage orphan cards (cards that exist in the database, but not in the
collection, i.e., cards that were deleted from the collection).
```bash
$ hashcards orphans list [DIRECTORY]
$ hashcards orphans delete [DIRECTORY]
```
Example:
```
$ hashcards orphans list Cards
04effc035b71692b66a90a622559479516526e7720c41afa22b29562915d58af
059e4e0fd5c3d0ab7ef0cc902cdc402a555ec4152b842fe584109de6c8082ce3
061b8c27e0f437d0c6ae735e829b39cc3bf0ad8218cb16387dcb4271c20b244d
$ hashcards orphans delete Cards
04effc035b71692b66a90a622559479516526e7720c41afa22b29562915d58af
059e4e0fd5c3d0ab7ef0cc902cdc402a555ec4152b842fe584109de6c8082ce3
061b8c27e0f437d0c6ae735e829b39cc3bf0ad8218cb16387dcb4271c20b244d
$ hashcards orphans list Cards
# no output
```
### `export`
Export a collection to a JSON file.
```bash
$ hashcards export [DIRECTORY]
```
Options:
- `--output=<PATH>`: The path to the output. By default, the export is printed
to stdout.
## Format
This section describes the text format used by hashcards.
### Basic Cards
Question-answer flashcards are written like this:
```
Q: What are the possible values of electric charge?
A: Any integer multiple of the fundamental charge.
```
Both the question and the answer can span multiple lines:
```
Q: List the elements of the Platinum group.
A:
- ruthenium
- rhodium
- palladium
- osmium
- iridium
- platinum
```
### Cloze Cards
Cloze cards start with the `C:` tag, and use square brackets to denote cloze
deletions:
```
C: The [order] of a group is [the cardinality of its underlying set].
```
Again, cloze cards can span multiple lines:
```
C:
Better is the sight of the eyes than the wandering of the
desire: this is also vanity and vexation of spirit.
— [Ecclesiastes] [6]:[9]
```
### Separators
Optionally, cards can be separated by horizontal rules, like so:
```
C: A semigroup with an identity element is called a [monoid].
---
C: A semigroup without associativity is called a [magma].
---
C: A magma where the operation is [associative] is called a [semigroup].
```
This can help visually separate the cards better.
## Features
This section documents specific hashcards features.
### LaTeX Support
Cards support LaTeX math via KaTeX.
Use `$...$` for inline math:
```
Q: What is the combinatorial meaning of $\binom{n}{k}$?
A: From a set of size $n$, we can choose $\binom{n}{k}$ subsets of size $k$.
```
And `$$...$$` for display math:
```
C: The [amount of substance] of a sample, denoted $n$, is defined as:
$$
n = \frac{N}{N_A}
$$
where $N$ is [the number of elementary entities] and $N_A$ is [Avogadro's constant].
```
You can define custom LaTeX macros by creating a `macros.tex` file in your
collection root:
```
\C \mathbb{C}
\R \mathbb{R}
```
Macro definitions can refer to arguments: `#1` for the first, `#2` for the
second and so on.
### Images
Ordinary Markdown image syntax works:
```
Q: Identify this painting:
A: _The Siren_, by John William Waterhouse.
```
By default, image paths are resolved relative to the deck (the Markdown file)
that contains the flashcard. For example, if you have:
```
cards/
Art Theory/
Art.md
Images/
TheMermaid.jpg
Circe.jpg
Odysseus.jpg
```
Then flashcards in `Art.md` can reference images with paths like
`Images/Circe.jpg`.
By prefixing a path with `@/`, you can point to images relative to the
collection root directory, e.g., a path like `@/Art Theory/Images/Circe.jpg`
will always resolve to the same path, even if the deck is moved around within
the collection.
### Audio
Works like images:
```
Q: How do you pronounce "پرنده" in Persian?
A: 
```
### Deck Names
By default, the filename of a deck is the name of a deck, e.g. a file
`Medicine.md` will be parsed as a deck called `Medicine`. It is possible to
override the name using [TOML](https://toml.io/en/) frontmatter, like so:
```
---
name = "Medicine"
---
C: The mitochondria is the [powerhouse] of the cell.
```
Regardless of the filename, cards in this deck will have `Medicine` as their
deck name. This is particularly useful when you want to organize a large number
of cards into different files, while keeping their deck name the same. For
example, when taking notes from a textbook, you might have something like so:
```
Principles of Neural Science/
Ch1.md
Ch2.md
...
```
But you don't want the cards in those Markdown files to have `Ch1`, `Ch2`, etc.
as their deck name. TOML frontmatter allows you to give each chapter deck the same
deck name.
### Sibling Burial
A single cloze card in the Markdown text with _n_ cloze deletions corresponds to _n_ distinct cloze cards in the database, one per deletion. These cards are called "siblings".
Hashcards supports "sibling burial": by default, within a session, only one sibling in a particular sibling group will be shown. This is to prevent the text of one card spoiling the answer of another card. The idea is you might do multiple sessions in a single day, and each session shows a different sibling, until you run out of siblings for all cards due today.
You can turn this off by passing `--bury-siblings=false` to the `drill` command.
## Database
hashcards stores card performance data and the review history in an SQLite3
database. The file is called `hashcards.db` and is found in the root of the card
directory (i.e., the path you pass to the `drill` command).
The `cards` table has the following schema:
| `card_hash` | `text primary key` | The hash of the card. |
| `added_at` | `text not null` | The timestamp when the card was first added to the database, in timestamp format. |
| `last_reviewed_at` | `text` | The timestamp when the card was most recently reviewed. `null` if the card is new. |
| `stability` | `real` | The card's stability. `null` if the card is new. |
| `difficulty` | `real` | The card's difficulty. `null` if the card is new. |
| `interval_raw` | `real` | The FSRS-calculated interval, before rounding and clamping. A real number of days until the next review. `null` if the card is new. |
| `interval_days` | `real` | The interval as an integer number of days, after rounding and clamping. `null` if the card is new. |
| `due_date` | `text` | The date when the card is next due, in `YYYY-MM-DD` format. `null` if the card is new. |
| `review_count` | `integer not null` | The number of times the card has been reviewed. |
The `sessions` table has the following schema:
| `session_id` | `integer primary key` | The ID of the session. |
| `started_at` | `text not null` | The timestamp when the session started, in timestamp format. |
| `ended_at` | `text not null` | The timestamp when the session ended, in timestamp format. |
The `reviews` table has the following schema:
| `review_id` | `integer primary key` | The review ID. |
| `session_id` | `integer not null` | The ID of the session this review was performed in, a foreign key. |
| `card_hash` | `text not null` | The hash of the card that was reviewed, a foreign key. |
| `reviewed_at` | `text not null` | The timestamp when the review was performed (i.e., when the user submitted a grade). |
| `grade` | `text not null` | One of `forgot`, `hard`, `good`, or `easy`. |
| `stability` | `real not null` | The card's stability after this review. |
| `difficulty` | `real not null` | The card's difficulty after this review. |
| `interval_raw` | `real` | The FSRS-calculated interval, before rounding and clamping. A real number of days until the next review `null` if the card is new. |
| `interval_days` | `real` | The interval as an integer number of days, after rounding and clamping. `null` if the card is new. |
| `due_date` | `text not null` | The date, in the user's local time, when the card is next due, in `YYYY-MM-DD` format. |
Note: "timestamp format" is `YYYY-MM-DDTHH:MM:SS.MMM`, e.g. `2025-10-04T17:09:51.517`.
## Prior Art
- [org-fc](https://github.com/l3kn/org-fc)
- [org-drill](https://orgmode.org/worg/org-contrib/org-drill.html)
- [hascard](https://hackage.haskell.org/package/hascard)
- [carddown](https://github.com/martintrojer/carddown)
- [My implementation of a personal mnemonic medium](https://notes.andymatuschak.org/My_implementation_of_a_personal_mnemonic_medium)
[FSRS]: https://github.com/open-spaced-repetition/fsrs4anki
[blog]: https://borretti.me/article/hashcards-plain-text-spaced-repetition
[cargo]: https://doc.rust-lang.org/cargo/
[esr]: https://borretti.me/article/effective-spaced-repetition
[fc]: https://github.com/eudoxia0/flashcards
[rustup]: https://rustup.rs/
## License
© 2025 by [Fernando Borretti][fb]. Licensed under the [Apache 2.0][apache2] license.
[fb]: https://borretti.me/
[apache2]: https://www.apache.org/licenses/LICENSE-2.0
