Zen

A spaced repetition CLI for active recall using the FSRS algorithm.

Features

• Simple card creation: Create flashcards directly from the command line
• Question-answer format: Focus on what matters - questions and answers
• FSRS algorithm: Uses the modern Free Spaced Repetition Scheduler for optimal learning
• Interactive review sessions: TUI-based review with real-time interval previews
• Fuzzy search: Find and edit cards with interactive fuzzy matching
• CLI-first: All interactions through the terminal
• Easy editing: Cards stored as simple markdown files
• Efficient storage: Hybrid approach with markdown for content and SQLite for scheduling

Installation

cargo install --git https://github.com/hamzamohdzubair/zen

Or clone and build from source:

git clone git@github.com:hamzamohdzubair/zen.git
cd zen
cargo build --release

Usage

Create a new card

zen new what is the relationship between vpc and vm in google cloud

You'll be prompted to enter the answer (multi-line supported). Press Enter twice to finish.

Find and edit cards

zen find google cloud    # Fuzzy search for cards
zen f google cloud       # Short alias

Opens an interactive fuzzy finder. Type to filter cards, use arrows/Tab to navigate, press Enter to edit in your default editor.

Start a review session

zen start

Reviews all cards that are due:

• Press Space or Enter to reveal the answer
• Rate your recall: 1 (Again), 2 (Hard), 3 (Good), 4 (Easy)
• Each rating shows the next review interval (e.g., 10m, 3d, 8d, 21d)
• Progress indicator shows your position (Card 3/10)
• Summary statistics displayed at the end

Future commands (coming soon)

zen stats                # Show statistics
zen list                 # List all cards

Card Storage

Cards are stored in ~/.zen/:

• Content: ~/.zen/cards/*.md - Simple markdown files
• Metadata: ~/.zen/zen.db - SQLite database for scheduling

Card Format

Cards use a minimal format:

What is your question?

---

This is the answer.

Everything before \n\n---\n\n is the question, everything after is the answer.

Roadmap

• Phase 1: Basic card creation and storage
• Phase 2: Fuzzy search and editing with TUI
• Phase 3: Review sessions with FSRS scheduling
• Phase 4: Statistics and polish
• Phase 5: Import/export and advanced features

See DESIGN.md for detailed feature planning.

How Reviews Work (FSRS)

Zen uses the FSRS (Free Spaced Repetition Scheduler) algorithm to optimize your review schedule:

1. New cards start with short intervals (minutes to days)
2. Each rating updates the card's memory parameters:
   • Stability: How long the memory lasts
   • Difficulty: The card's inherent difficulty
   • Retrievability: Your current memory strength
3. Next review date is calculated to maintain 90% retention probability
4. Four rating options:
   • 1 - Again: Failed recall (review soon, ~10m)
   • 2 - Hard: Difficult recall (~3d)
   • 3 - Good: Correct with effort (~8d)
   • 4 - Easy: Perfect recall (~21d)

Intervals shown are examples for new cards. The algorithm adapts based on your actual performance history.

Design Principles

• No full-screen interfaces: All TUIs are max half-terminal height
• Vim-like navigation: Ctrl+j/k for movement
• No quotes needed: Natural command syntax
• Easy editing: Edit cards in your favorite editor
• Non-invasive: Minimal, focused interface

Development

Build

cargo build --release

Test

cargo test

Run

cargo run -- new your question here

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.