Syncthing

Syncthing keeps a folder identical across two or more of your own devices, without routing that data through a company’s cloud first. There’s no account and no central server in the middle: your laptop, phone, and home server talk directly to each other over an encrypted connection, and a file dropped into a shared folder on one shows up on the others within seconds. Dropbox and Google Drive sell you cloud storage with sync bundled on top; Syncthing does only the sync part, peer-to-peer, on hardware you already own.

How Syncthing works: no server involved

Most self-hosted file tools, Nextcloud included, run a server: install it once, and every device connects to that instance. Syncthing skips the server. Each device generates its own TLS certificate on first start and gets a Device ID, the SHA-256 fingerprint of that certificate. Add another device’s ID on both ends and the two instances connect directly, verify each other against that fingerprint, and sync over TLS 1.2/1.3. There’s no password to steal in transit, because there’s no account layer to attack.

Syncing is incremental: only changed blocks in a file cross the wire, not the whole file every time. Local discovery finds devices on your LAN with no internet needed; global discovery does the same over the internet, encrypted. When a direct connection isn’t possible, community relay servers pass traffic through instead, still end-to-end encrypted, just slower. All three are opt-out, documented on Syncthing’s own security principles page.

Installing Syncthing with Docker

The official syncthing/syncthing image builds from the project’s own Dockerfile, on Docker Hub and mirrored to ghcr.io/syncthing/syncthing. One container is the entire install: no database, nothing else to babysit.

services:
  syncthing:
    image: syncthing/syncthing
    container_name: syncthing
    hostname: syncthing
    environment:
      - PUID=1000
      - PGID=1000
    volumes:
      - ./syncthing-config:/var/syncthing
    network_mode: host
    restart: unless-stopped

PUID and PGID set which user and group the container writes files as (1000 matches the first regular user on most Linux distributions). Adjust them, then bring the stack up:

docker compose up -d

Syncthing setup: pairing your first two devices

1. Open the web GUI on each device: http://server-ip:8384 for the Docker host, http://localhost:8384 if Syncthing runs natively on the second machine.
2. On each device, open Actions, then Show ID, to get its Device ID.
3. On device A, click Add Remote Device and paste device B’s ID.
4. Repeat in reverse on device B. Connections are always mutual.
5. Once connected, usually within a minute, share a folder from one side; the other device gets a popup to accept it, and syncing starts.

Syncthing vs Nextcloud

Syncthing and Nextcloud get compared constantly, though they solve different problems more often than they compete. Nextcloud is client-server: install it once, and every device connects to that instance for files, calendars, contacts, and chat. Syncthing only keeps folders identical across devices you own; there’s no server to browse from a friend’s computer, no public link to email someone. Where they overlap, Syncthing tends to be faster and lighter, since it isn’t running a web app, database, and job queue underneath the sync feature.

	Syncthing	Nextcloud
Architecture	Peer-to-peer, no central server	Client-server, one instance to maintain
Best at	Keeping folders identical across your own devices	Files, calendar, contacts, chat, and office docs together
Public link sharing	Not built in, no server to host one	Yes, with passwords and expiry dates
Resource footprint	One lightweight Go binary, no database	PHP, a database, and Redis beyond a toy install
Mobile access	Community Android and iOS apps (original Android app discontinued)	Official iOS and Android apps with remote browsing

Syncthing: pros and cons

• No account and no central server; nobody but you holds a copy of your files
• Incremental, block-level sync makes catching up after time offline fast
• Runs comfortably on a Raspberry Pi or the smallest box in a homelab
• Traffic is TLS-encrypted device to device, even through a relay

• No public link sharing or web file browser away from a device you control
• The original official Android app was discontinued; mobile now runs on community apps
• Pairing by Device ID is a different mental model than logging into a website
• Nothing to browse from someone else’s computer without installing Syncthing there too

If typing docker compose commands isn’t appealing, Portainer gives the container a point-and-click restart button and log viewer instead.

FAQ

Is Syncthing free?

Yes, fully. Open source under the Mozilla Public License 2.0, no paid tier, no feature paywall anywhere in the project.

Is Syncthing safe to use?

The sync connection is solid: TLS 1.2/1.3 between devices, mutual authentication by certificate fingerprint, no account database to breach. The web GUI is the part worth watching, since the Docker image exposes it on every interface by default. Set a GUI password immediately.

Do I need to open ports on my router?

Only for two devices on different networks to connect directly at full speed: forward 22000/TCP and 22000/UDP. Without it, Syncthing falls back to relay servers automatically, slower but working.

Can Syncthing back up my phone’s photos automatically?

Yes, a community Android app can watch your camera folder and sync new photos as they’re taken, but it won’t do face recognition or search by content. For that, Immich is built around AI-powered photo search and backup.

What’s the real difference between Syncthing and Nextcloud?

Syncthing keeps folders identical across your own devices and stops there. Nextcloud is a full platform, files plus calendar, contacts, and chat, accessed through one central server from anywhere. Plenty of homelabs run both: Syncthing for fast device-to-device sync, Nextcloud for anything needing a proper web interface or sharing with other people.

Syncthing earns its place in a homelab by doing one thing well and staying out of the way otherwise. Our homelab setup guide for beginners covers the hardware it needs, and if a fuller collaboration suite is what you’re after, Nextcloud is the natural next stop.