Syncthing

What is Syncthing?

Syncthing is an open source program that continuously synchronizes files between your own devices. Instead of uploading to a central cloud, each device talks directly to the others over an encrypted connection — you pair two machines by exchanging device IDs, pick which folders to share, and changes propagate between them in real time.

What is Syncthing best for?

People who want their files on every device without trusting a third-party cloud — laptops, desktops, home servers, and Android phones kept in sync on a home or office network. It shines when your devices are frequently online together and you care more about privacy and control than about sharing links with outside collaborators.

What can Syncthing do?

• Sync unlimited folders directly between devices with no central server and no storage limits beyond your own disks
• Encrypt every transfer with TLS and perfect forward secrecy, authenticating each device by a unique cryptographic ID
• Keep deleted and changed files with configurable file versioning (trash-can, staggered, or simple)
• Run on Windows, macOS, Linux, FreeBSD, and more, plus an official Android app and a Docker image
• Manage everything from a browser-based web GUI — add devices, share folders, watch sync status
• Traverse NAT automatically using UPnP, relay servers, and global/local discovery, so most setups need no manual port forwarding
• Share a folder with an untrusted device using encrypted (send-only-encrypted) folders, so a remote peer can hold your data without being able to read it

Where does Syncthing fall short?

• It is not a backup tool and there is no always-on cloud copy. Because sync is peer-to-peer, at least two of your devices must be online at the same time for changes to move — if everything is off, nothing syncs. To get a “cloud” that’s always available you have to run your own always-on node.
• Deletions and edits propagate like any change, so a mistake spreads to your other devices; file versioning is your safety net, but it’s off for new folders until you enable it.
• There are no built-in public share links for people who don’t run Syncthing. It syncs between your devices, not with external collaborators the way Dropbox or Google Drive share a link.
• There is no official iOS app — iPhone and iPad users depend on third-party apps, and background sync on mobile is more limited than on desktop.

Is Syncthing free?

Yes — Syncthing is completely free and open source under the MPL-2.0 license, with no paid tiers, storage fees, or account to create. You only pay for the hardware and bandwidth you already own. Kastelo, run by the maintainers, sells optional commercial support, but the software itself is unrestricted.

What does Syncthing replace?

Syncthing is a self-hosted alternative to Dropbox and Google Drive for the sync half of what they do — keeping the same folder mirrored across your machines. It deliberately skips the hosted-cloud, web-link-sharing, and online-document side of those services. If you need a central web UI, sharing links, and always-available storage, a full suite like Nextcloud or Seafile is a closer match; if you just want private folder sync, Syncthing is lighter and simpler.

FAQ

Is Syncthing open source? Yes. It’s licensed under the MPL-2.0 (Mozilla Public License 2.0), an OSI-approved open source license, and the full source is public on GitHub.

Can I use Syncthing for free? Yes — it’s free with no limits on devices, folders, or data. Your only cost is the storage and bandwidth on the devices you run it on.

Is Syncthing a good Dropbox alternative? For private sync between your own devices, yes — it’s faster on a local network and keeps no copy in anyone else’s cloud. It’s a weaker fit if you rely on share links, web access, or an always-online backup, since it has none of those by default.

What do I need to run Syncthing? Two or more devices (Windows, macOS, Linux, or Android) running the app. It’s a single lightweight binary with a web UI; a home server or spare always-on machine helps if you want files to sync even when your other devices are asleep.