Education beginner ⏱ 30 minutes

Anki Sync Server: Flashcard Synchronization

Self-hosted Anki sync for spaced repetition. Sync flashcards across all devices.

By Homelab Team • 2025-01-15
#anki#flashcards#sync#learning#docker

Anki is the world’s most popular spaced repetition software, helping millions of students, professionals, and lifelong learners master everything from medical school curricula to foreign languages. This guide shows you how to deploy your own Anki sync server to keep your flashcard data private while syncing across all your devices.

What is Anki?

Anki is a powerful flashcard application that uses spaced repetition algorithms to optimize learning and long-term retention. Unlike traditional flashcard apps, Anki schedules reviews at scientifically-proven intervals to maximize memory consolidation while minimizing study time.

Why Self-Host Anki Sync Server?

Privacy and Data Ownership:

  • AnkiWeb free tier: 300MB storage limit, data stored on third-party servers
  • Self-hosted: Unlimited storage, complete data control
  • No sharing of study patterns or learning data
  • Full compliance with institutional data policies

Unlimited Storage:

  • AnkiWeb paid tier: $27/year for increased storage
  • Self-hosted: Only limited by your server capacity
  • Store high-resolution images, audio files, videos
  • Large medical image decks (radiology, pathology)
  • Language learning with extensive audio

Performance Benefits:

  • Faster sync speeds on local network
  • No dependency on external service availability
  • Reduced latency for large deck syncs
  • Control over server resources and optimization

Institutional and Team Use:

  • Deploy for entire organization
  • No per-user subscription costs
  • Custom backup and retention policies
  • Integration with existing authentication systems

How Spaced Repetition Works

Anki implements the SuperMemo SM-2 algorithm:

  1. New cards: Shown for first time
  2. Learning cards: Recently introduced, shown frequently
  3. Review cards: Mastered cards shown at increasing intervals
  4. Lapsed cards: Cards you forgot, re-entered learning phase

Example Learning Timeline:

Day 1: Study new card "What is Docker?"
Day 2: Review (if correct, interval increases)
Day 4: Review (interval doubles)
Day 8: Review
Day 16: Review
Day 32: Review
...continues with increasing intervals

This scientifically-proven approach ensures:

  • 90%+ retention rates
  • Minimal study time for maximum retention
  • Automatic difficulty adjustment
  • Long-term memory consolidation

Prerequisites

Before deploying your Anki sync server:

System Requirements:

  • Docker and Docker Compose installed
  • 512MB RAM minimum (1GB+ recommended)
  • 1 CPU core (adequate for personal use)
  • 10GB+ storage (grows with deck content)
  • Ubuntu 22.04 LTS or similar Linux distribution

Software Requirements:

  • Anki Desktop application (Windows, Mac, or Linux)
  • Anki Mobile app (iOS or Android) - optional
  • Basic command-line knowledge
  • Understanding of Docker concepts

Network Requirements:

  • Static local IP or DHCP reservation
  • Port 27701 available (default sync port)
  • Optional: Domain name for remote access

Understanding Anki Architecture

Components:

Anki Desktop/Mobile:

  • Client application for studying
  • Creates and edits flashcards
  • Tracks study statistics
  • Initiates sync with server

Sync Server:

  • Stores deck data and media
  • Handles synchronization requests
  • Manages user accounts
  • Coordinates cross-device sync

Database:

  • SQLite-based storage
  • Stores cards, reviews, statistics
  • Media files (images, audio, video)
  • User preferences and settings

Sync Flow:

Anki Desktop (Computer)
      |
      v
[Sync Server] Port 27701
      |
      v
[Database Storage]
      |
      v
Anki Mobile (Phone/Tablet)

Installation and Deployment

Step 1: Choose Sync Server Implementation

Two popular options exist:

anki-sync-server (Official):

  • Official implementation by Anki developers
  • Python-based
  • Stable and well-maintained
  • Recommended for most users

anki-sync-server-rs (Rust):

  • Community implementation in Rust
  • Higher performance
  • Lower resource usage
  • Good for resource-constrained environments

This guide uses the official Python implementation.

Step 2: Directory Preparation

Create project directory:

# Create directory structure
mkdir -p ~/anki-sync-server/data

# Set permissions
chmod -R 755 ~/anki-sync-server

Step 3: Docker Compose Configuration

Create ~/anki-sync-server/docker-compose.yml:

version: '3.8'

services:
  anki-sync-server:
    image: ankicommunity/anki-sync-server:latest
    container_name: anki-sync-server
    restart: unless-stopped
    environment:
      # Server Configuration
      ANKISYNCD_HOST: 0.0.0.0
      ANKISYNCD_PORT: 27701

      # Authentication
      ANKISYNCD_AUTH_DB_PATH: /data/auth.db
      ANKISYNCD_SESSION_DB_PATH: /data/session.db

      # Data Storage
      ANKISYNCD_DATA_ROOT: /data

      # Optional: Enable HTTPS (requires certificates)
      # ANKISYNCD_USE_HTTPS: "true"
      # ANKISYNCD_CERT_FILE: /certs/cert.pem
      # ANKISYNCD_KEY_FILE: /certs/key.pem
    ports:
      - "27701:27701"
    volumes:
      - ./data:/data
    networks:
      - anki-network

networks:
  anki-network:
    driver: bridge

Configuration Notes:

  • Port 27701: Standard Anki sync port
  • Volume ./data: Stores all user data and decks
  • Restart policy ensures availability after reboots

Alternative: Rust Implementation (Optional)

For higher performance, use the Rust version:

version: '3.8'

services:
  anki-sync-server:
    image: ghcr.io/ankicommunity/anki-sync-server-rs:latest
    container_name: anki-sync-server
    restart: unless-stopped
    environment:
      ANKISYNCD_PORT: 27701
      ANKISYNCD_HOST: 0.0.0.0
      MAX_SYNC_PAYLOAD_MEGS: 100
    ports:
      - "27701:27701"
    volumes:
      - ./data:/data
    networks:
      - anki-network

networks:
  anki-network:
    driver: bridge

Step 4: Deploy Sync Server

# Navigate to project directory
cd ~/anki-sync-server

# Pull Docker image
docker-compose pull

# Start service
docker-compose up -d

# Verify startup
docker-compose logs -f

Look for successful startup message:

Anki Sync Server started on 0.0.0.0:27701

Step 5: Verify Deployment

# Check container status
docker-compose ps
# Should show "Up"

# Check logs
docker-compose logs anki-sync-server

# Test network accessibility
curl http://YOUR-SERVER-IP:27701
# Should return Anki sync server response

Step 6: Create User Accounts

Add Your First User:

# Enter container
docker exec -it anki-sync-server sh

# Add user (replace username and password)
ankisyncctl adduser YOUR-USERNAME
# Enter password when prompted

# Exit container
exit

Alternative: Command-line User Creation:

docker exec -it anki-sync-server ankisyncctl adduser YOUR-USERNAME

Create Multiple Users:

# Add family members or team members
docker exec -it anki-sync-server ankisyncctl adduser alice
docker exec -it anki-sync-server ankisyncctl adduser bob
docker exec -it anki-sync-server ankisyncctl adduser charlie

List Users:

docker exec -it anki-sync-server ankisyncctl lsuser

Delete User:

docker exec -it anki-sync-server ankisyncctl deluser USERNAME

Desktop Client Configuration

Anki Desktop Setup (Windows, Mac, Linux)

Install Anki Desktop:

  1. Download from apps.ankiweb.net
  2. Install latest stable version (2.1.60+)
  3. Launch Anki

Configure Sync Server:

Anki 2.1.60+ (newest versions):

  1. Open Anki
  2. Go to Tools → Preferences → Network
  3. Self-hosted sync server section:
    • Enable: Check “Use custom sync server”
    • Sync URL: http://YOUR-SERVER-IP:27701/
    • Media URL: http://YOUR-SERVER-IP:27701/msync
  4. Click OK

Older Anki Versions (2.1.28-2.1.59):

Create addon file to configure server:

  1. Tools → Add-ons → View Files
  2. Create folder: ankisyncd
  3. Inside folder, create __init__.py:
import anki.sync

# Configure sync server
anki.sync.SYNC_URL = "http://YOUR-SERVER-IP:27701/"
anki.sync.SYNC_MEDIA_URL = "http://YOUR-SERVER-IP:27701/msync"
  1. Restart Anki

First Sync

Initial Synchronization:

  1. Click Sync button (top right)
  2. Enter credentials:
    • AnkiWeb ID: YOUR-USERNAME (from earlier setup)
    • Password: Your password
  3. First sync prompt:
    • “Upload to sync server” (if you have existing decks)
    • “Download from sync server” (if server has your decks)
  4. Wait for sync to complete

Subsequent Syncs:

  • Click Sync button anytime
  • Automatic sync on startup (if enabled in preferences)
  • Automatic sync on close (if enabled)

Sync Settings Optimization

Tools → Preferences → Network:

Synchronization:
├─ Sync on profile open: Yes (recommended)
├─ Sync on profile close: Yes (recommended)
├─ Sync media: Yes (includes images/audio)
├─ Check for updates: No (optional)
└─ Periodically sync media: Yes

Media Sync: Large media libraries take time on first sync:

  • Medical images: 1-2 hours for 10GB
  • Language audio: 30-60 minutes for 5GB
  • Subsequent syncs: Only changed files

Mobile App Configuration

iOS (AnkiMobile)

Purchase and Install:

  1. AnkiMobile costs $24.99 (one-time purchase)
  2. Download from iOS App Store
  3. Install and launch

Configure Sync Server:

  1. Open AnkiMobile
  2. Tap Settings (gear icon)
  3. Tap Synchronization
  4. Sync Server section:
    • Custom sync server: Enable
    • Sync URL: http://YOUR-SERVER-IP:27701/
    • Media URL: http://YOUR-SERVER-IP:27701/msync/
  5. Return to main screen

First Sync:

  1. Tap Sync button
  2. Enter credentials (username/password)
  3. Choose sync direction:
    • Download from server (recommended for first mobile sync)
  4. Wait for completion

Android (AnkiDroid)

Install AnkiDroid:

  1. Free on Google Play Store
  2. Install and launch

Configure Custom Sync Server:

  1. Open AnkiDroid
  2. Tap menu (three lines) → Settings
  3. Tap Advanced
  4. Scroll to Custom sync server
  5. Enable custom sync server
  6. Configure:
    • Sync URL: http://YOUR-SERVER-IP:27701/
    • Media sync URL: http://YOUR-SERVER-IP:27701/msync/
  7. Back to main screen

First Sync:

  1. Tap Sync button (circular arrows)
  2. Enter AnkiWeb credentials:
    • ID: YOUR-USERNAME
    • Password: Your password
  3. Choose “Download from AnkiWeb” (for first sync)
  4. Wait for sync completion

Note: AnkiDroid may require HTTP instead of HTTPS for local servers. If using a domain with SSL, ensure certificate is valid.

Deck Organization Best Practices

Creating Effective Decks

Deck Structure Example (Medical Student):

Medicine
├── Anatomy
│   ├── Cardiology
│   ├── Neurology
│   └── Musculoskeletal
├── Physiology
│   ├── Cardiovascular
│   └── Respiratory
├── Pharmacology
│   ├── Antibiotics
│   └── Cardiovascular Drugs
└── Clinical Skills
    ├── Physical Exam
    └── Differential Diagnosis

Language Learning Example:

Spanish
├── Vocabulary
│   ├── Common Words (1000)
│   ├── Verbs
│   └── Phrases
├── Grammar
│   ├── Verb Conjugation
│   └── Sentence Structure
└── Pronunciation
    └── Audio Practice

Card Creation Tips

Effective Card Format:

Good Card (Simple, focused):

Q: Capital of France?
A: Paris

Bad Card (Too complex):

Q: What are the capitals of France, Germany, and Spain, and what are their populations?
A: Paris (2.1M), Berlin (3.7M), Madrid (3.2M)

Use Cloze Deletions:

Docker is a {{c1::containerization}} platform that allows you to {{c2::package applications}} with their dependencies.

Add Images for Visual Learners:

Q: [Image of heart diagram]
What structure is indicated by the arrow?

A: Left ventricle

Include Audio for Languages:

Q: How do you pronounce "croissant"?
A: [Audio file: croissant.mp3]
Translation: Crescent roll

Shared Deck Import

Download Shared Decks:

  1. Visit ankiweb.net/shared/decks
  2. Search for topic (e.g., “MCAT”, “Spanish”, “Programming”)
  3. Download .apkg file
  4. Anki Desktop → File → Import
  5. Select downloaded file
  6. Sync to propagate to all devices

Popular Shared Decks:

  • AnKing Medical Deck (30,000+ cards)
  • Ultimate Geography (4,700+ countries/capitals)
  • Core 2K/6K/10K Japanese Vocabulary
  • Programming concepts and syntax
  • Professional certifications (AWS, CCNA, etc.)

User Management

Adding Users

Family or Team Setup:

# Add family members
docker exec -it anki-sync-server ankisyncctl adduser mom
docker exec -it anki-sync-server ankisyncctl adduser dad
docker exec -it anki-sync-server ankisyncctl adduser daughter
docker exec -it anki-sync-server ankisyncctl adduser son

# Each user gets:
# - Separate deck storage
# - Individual study statistics
# - Private flashcard content

User Data Isolation

Each user’s data is completely isolated:

  • Separate SQLite databases
  • Individual media directories
  • Private study statistics
  • No cross-user data access

Data Structure:

~/anki-sync-server/data/
├── auth.db (authentication database)
├── session.db (active sessions)
├── collections/
│   ├── user1/
│   │   ├── collection.anki2 (deck database)
│   │   └── media/ (images, audio)
│   ├── user2/
│   └── user3/

Password Management

Change User Password:

# Change password for existing user
docker exec -it anki-sync-server ankisyncctl passwd USERNAME
# Enter new password when prompted

Password Policy Recommendations:

  • Minimum 12 characters
  • Mix of letters, numbers, symbols
  • Unique password (not reused)
  • Store in password manager

Backup Procedures

What to Backup

Critical data to preserve:

User Collections:

  • /data/collections/: All user decks and study data
  • Priority: CRITICAL

Authentication Database:

  • /data/auth.db: User credentials
  • Priority: HIGH

Media Files:

  • /data/collections/*/media/: Images, audio, video
  • Priority: HIGH (often largest component)

Session Database:

  • /data/session.db: Active login sessions
  • Priority: LOW (regenerates)

Automated Backup Script

Create ~/anki-sync-server/backup.sh:

#!/bin/bash

# Configuration
BACKUP_DIR="/backups/anki"
DATE=$(date +%Y%m%d_%H%M%S)
RETENTION_DAYS=30
ANKI_DATA="$HOME/anki-sync-server/data"

# Create backup directory
mkdir -p $BACKUP_DIR

echo "Starting Anki sync server backup: $(date)"

# Stop container for consistent backup (optional)
# cd ~/anki-sync-server
# docker-compose stop anki-sync-server

# Backup entire data directory
echo "Backing up Anki data..."
tar -czf $BACKUP_DIR/anki-data-$DATE.tar.gz   -C $HOME/anki-sync-server   data

if [ $? -eq 0 ]; then
    echo "Backup completed successfully"
else
    echo "Backup FAILED"
    exit 1
fi

# Restart container
# docker-compose start anki-sync-server

# Backup docker-compose configuration
cp ~/anki-sync-server/docker-compose.yml   $BACKUP_DIR/docker-compose-$DATE.yml

# Calculate backup size
BACKUP_SIZE=$(du -h $BACKUP_DIR/anki-data-$DATE.tar.gz | cut -f1)
echo "Backup size: $BACKUP_SIZE"

# Remove old backups
echo "Cleaning old backups..."
find $BACKUP_DIR -name "anki-data-*.tar.gz" -mtime +$RETENTION_DAYS -delete
find $BACKUP_DIR -name "docker-compose-*.yml" -mtime +$RETENTION_DAYS -delete

echo "Backup completed: $(date)"
echo "Location: $BACKUP_DIR/anki-data-$DATE.tar.gz"

Make Executable:

chmod +x ~/anki-sync-server/backup.sh

Test Backup:

~/anki-sync-server/backup.sh

Schedule Automated Backups:

# Edit crontab
crontab -e

# Add daily backup at 3 AM
0 3 * * * /home/user/anki-sync-server/backup.sh >> /var/log/anki-backup.log 2>&1

Disaster Recovery

Restore from Backup:

# Stop sync server
cd ~/anki-sync-server
docker-compose down

# Backup current data (safety measure)
mv data data.old

# Extract backup
tar -xzf /backups/anki/anki-data-YYYYMMDD_HHMMSS.tar.gz   -C ~/anki-sync-server

# Restore permissions
chmod -R 755 ~/anki-sync-server/data

# Start sync server
docker-compose up -d

# Verify restoration
docker-compose logs -f

Verify Data Integrity:

# Check user databases exist
ls -lh ~/anki-sync-server/data/collections/

# Verify user authentication
docker exec -it anki-sync-server ankisyncctl lsuser

Export Individual Decks

From Anki Desktop:

  1. File → Export
  2. Select deck to export
  3. Format: Anki Deck Package (.apkg)
  4. Include: All cards, scheduling information, media
  5. Save to secure location

This creates portable backup of specific decks.

Troubleshooting

Common Issues and Solutions

Issue: Cannot Connect to Sync Server

Diagnostics:

# Check container running
docker-compose ps

# Check logs
docker-compose logs anki-sync-server

# Test network connectivity
curl http://YOUR-SERVER-IP:27701

# Check firewall
sudo ufw status

Solutions:

  • Ensure container running: docker-compose up -d
  • Allow port through firewall: sudo ufw allow 27701/tcp
  • Verify correct IP address in client configuration
  • Check no other service using port 27701: sudo netstat -tlnp | grep 27701

Issue: Authentication Failed

Solutions:

  1. Verify credentials:
# List users
docker exec -it anki-sync-server ankisyncctl lsuser
  1. Reset password:
docker exec -it anki-sync-server ankisyncctl passwd USERNAME
  1. Check auth database:
# Verify database exists
ls -lh ~/anki-sync-server/data/auth.db
  1. Recreate user if needed:
docker exec -it anki-sync-server ankisyncctl deluser USERNAME
docker exec -it anki-sync-server ankisyncctl adduser USERNAME

Issue: Sync Fails with “Conflict” Error

Solutions:

  • Force sync direction:
    • Desktop: Tools → Preferences → Network → Sync → Upload/Download
    • Mobile: Sync settings → Full sync → Upload/Download
  • Ensure only one device syncing at a time
  • Check adequate storage space on server

Issue: Media Files Not Syncing

Solutions:

  1. Verify media sync enabled:

    • Desktop: Tools → Preferences → Network → Sync media: Yes
    • Mobile: Settings → Sync media: Enabled

  2. Check disk space:

df -h ~/anki-sync-server/data
  1. Verify media directory permissions:
ls -lh ~/anki-sync-server/data/collections/USERNAME/media/
  1. Manual media sync:
    • Anki Desktop: Tools → Check Media
    • Fix any issues reported
    • Sync again

Issue: Slow Sync Performance

Solutions:

  1. Initial sync is always slow (full deck transfer)
  2. Subsequent syncs only transfer changes (fast)
  3. Optimize large media files:
    • Compress images (JPG instead of PNG)
    • Use lower bitrate audio files
    • Resize images to reasonable dimensions
  4. Sync over wired connection when possible
  5. Increase container resources if constrained

Issue: Lost Sync Button or Sync Not Working

Solutions:

  • Tools → Preferences → Network → Verify server URLs correct
  • Restart Anki Desktop
  • Check internet/network connectivity
  • Verify sync server container running
  • Review sync server logs for errors

Remote Access Configuration

Secure access from anywhere without port forwarding.

Install Tailscale on Server:

curl -fsSL https://tailscale.com/install.sh | sh
sudo tailscale up

Get Tailscale IP:

tailscale ip -4
# Returns: 100.x.y.z

Configure Clients:

  1. Install Tailscale on all devices (desktop, mobile)
  2. Login to same account
  3. Update Anki sync URL to Tailscale IP:
    • http://100.x.y.z:27701/

Benefits:

  • No port forwarding needed
  • Encrypted VPN tunnel
  • Works from any network
  • Free for personal use

Option 2: Reverse Proxy with SSL

For public domain access with HTTPS.

Using Caddy:

Create /opt/caddy/Caddyfile:

anki.yourdomain.com {
    reverse_proxy YOUR-SERVER-IP:27701
}

Configure Anki Clients:

  • Sync URL: https://anki.yourdomain.com/
  • Media URL: https://anki.yourdomain.com/msync/

DNS Configuration:

  • Create A record: anki.yourdomain.com → Your public IP
  • Forward ports 80 and 443 to server

Security Considerations:

  • Use strong passwords
  • Consider rate limiting
  • Monitor access logs
  • Regular security updates

Advanced Configuration

Performance Tuning

Increase Max Payload Size:

For users with very large decks:

environment:
  MAX_SYNC_PAYLOAD_MEGS: 500  # Default is 100MB

Resource Limits:

services:
  anki-sync-server:
    # ... existing config ...
    deploy:
      resources:
        limits:
          memory: 1G
          cpus: '1.0'
        reservations:
          memory: 256M

Multi-User Organization

For Families:

  • Each family member has separate account
  • Private study data
  • Shared server infrastructure
  • Coordinate backup schedules

For Study Groups:

  • Individual accounts for each member
  • Share deck files manually (export/import)
  • Collaborative deck development
  • Group study statistics tracking

For Institutions:

  • Departmental deployment
  • Centralized backup management
  • User provisioning workflows
  • Integration with directory services

Study Tips and Best Practices

Effective Use of Spaced Repetition

Daily Study Routine:

  1. Review all due cards (reviews first priority)
  2. Study new cards (20-30 per day recommended)
  3. Use “Hard”, “Good”, “Easy” ratings honestly
  4. Don’t skip days (consistency crucial)

Optimize Deck Settings:

  • New cards per day: 20-30 (sustainable long-term)
  • Maximum reviews per day: Unlimited (must clear due cards)
  • Learning steps: 1m 10m 1d (or customize)
  • Graduating interval: 3 days
  • Easy interval: 4 days

Avoid Common Mistakes:

  • Don’t create cards that are too complex
  • Don’t study more than 1-2 hours per day (burnout risk)
  • Don’t skip reviews (breaks spaced repetition)
  • Don’t ignore “Hard” button (use full rating scale)

Mobile Study Workflow

Best Practices:

  1. Sync before studying
  2. Study during commute, breaks, downtime
  3. Sync after studying
  4. Enable offline mode for subway/airplane
  5. Use audio cards for walking/driving (careful)

Mobile-Specific Settings:

  • AnkiMobile: Settings → Study → Tap to reveal
  • AnkiDroid: Settings → Reviewing → Gesture controls
  • Optimize for one-handed use
  • Use night mode for evening study

Next Steps

Immediate Actions

After completing setup:

  1. Create user account and test sync from desktop
  2. Import first deck or create practice deck
  3. Sync to mobile device and verify
  4. Set up automated backups and test restore
  5. Study consistently for 7 days to establish habit

Expansion Ideas

Personal Learning:

  • Medical school preparation (AnKing deck)
  • Language acquisition (Core vocabulary)
  • Professional certification study
  • Hobby knowledge building

Family Learning:

  • Children’s education support
  • Homeschool curriculum reinforcement
  • Family trivia and games
  • Shared knowledge building

Professional Development:

  • Technical skill mastery
  • Industry certifications
  • Product knowledge training
  • Compliance and safety training

Conclusion

You now have a private, self-hosted Anki sync server providing unlimited storage and complete data control. Combined with Anki’s proven spaced repetition algorithm, you have a powerful foundation for lifelong learning across all your devices.

Key Achievements

  • Self-hosted sync server with unlimited storage
  • Multi-device synchronization (desktop + mobile)
  • User account management
  • Automated backup system
  • Remote access configured
  • Privacy-preserving architecture

Resources

Official Resources:

  • apps.ankiweb.net: Anki desktop downloads
  • docs.ankiweb.net: Complete documentation
  • ankiweb.net/shared: Shared deck library

Community Support:

  • r/Anki: Reddit community (140k+ members)
  • Anki forums: Official discussion boards
  • YouTube: Study technique tutorials

Recommended Decks:

  • Medical: AnKing, Sketchy, Pixorize
  • Languages: Core 2K/6K, Grammar decks
  • Tech: AWS, Programming languages, Networking
  • General: Ultimate Geography, History timelines

Start with small, achievable goals. Study 20 new cards daily, review all due cards, and maintain consistency. The spaced repetition algorithm will handle the rest, optimizing your learning for maximum long-term retention with minimum time investment.

Welcome to evidence-based, self-directed learning!