Syncthing is an open-source file synchronization program that continuously mirrors folders between two or more computers in real time. It needs no central server, so files move directly between your own devices over encrypted peer-to-peer connections.
Syncthing is a continuous file synchronization program that keeps folders identical across the computers you own. You install it on each machine, exchange a cryptographic device ID between them, and share a folder; from that point every change is detected and copied to the other side automatically. There is no account, no subscription and no central server holding a copy of your data, because devices connect directly over your local network or the internet using TLS. A browser interface on localhost:8384 handles folder, device and versioning settings. Typical workflows include keeping a laptop and desktop in step, syncing a photo library to a home server, or replicating documents onto a machine reserved for backups.
Because synchronization is peer-to-peer, throughput depends on the link between your own machines rather than on a third-party service. On a local network, transfers usually run at LAN speed, and after the first scan only changed blocks and metadata travel. Each folder can be set to send and receive, send only, or receive only, which suits feeding a read-only archive. Ignore patterns keep build artefacts, caches and temporary files out of the sync, and four versioning strategies archive replaced or deleted files instead of discarding them. When the same file changes on two devices at once, a conflict copy is created for manual review. Teams already relying on a Desktop Connector to bridge machines can let Syncthing handle bulk folder replication behind it.
Syncthing gives you private synchronization without renting storage from anyone. Nothing is uploaded to a company account, there is no monthly quota, and no provider can scan, throttle or shut down your sync. Data moves only between devices you authorized, and every connection is authenticated with per-device certificates and encrypted with TLS, so even a relay path cannot read your files. The setup cost is low: two machines, one device ID exchange, one shared folder, and syncing begins. It scales from a pair of laptops to a fleet of servers, and each folder holds independent settings, so a photos directory can keep a year of versions while a code directory keeps none. Because it runs across a wide range of operating systems, mixed environments of Windows desktops, Linux servers, macOS workstations and NAS boxes can all join the same cluster. Transfers continue unattended, resume after restarts, and repair missing or damaged files from other devices, which makes it a dependable backbone for backup and multi-machine work.
File watchers detect additions, edits, renames and deletions as they happen and push them to paired devices within seconds, so folders stay consistent without scheduled jobs or manual copying. A periodic full rescan runs as a safety net on platforms where filesystem notifications are unreliable, catching anything a watcher missed during a busy session.
Devices locate one another through public discovery servers and then connect directly over TCP or QUIC, falling back to community relays when both peers sit behind NAT. Your files never pass through a storage provider, and sync keeps working over a local network even when the discovery service is unreachable. Transfer rates and priorities can be tuned per device.
Each device generates its own certificate and a unique device ID derived from it, and pairing requires both sides to enter the other's ID. Connections are mutually authenticated and encrypted with TLS, so eavesdroppers on a shared network cannot read file contents or inject data into the sync.
Every shared folder can run in send-and-receive, send-only or receive-only mode. A send-only folder publishes changes but refuses incoming ones, which suits a machine that only delivers data, while a receive-only folder mirrors a source as an archive that local edits cannot disturb. Folder types are set per device, so one folder can behave differently on each machine in the cluster.
Four versioning strategies, trash can, simple, staggered and external, archive replaced or deleted files in a versions folder instead of losing them. Staggered keeps the oldest copy from each interval, preserving hourly, daily and weekly snapshots up to a maximum age you choose, while external versioning passes the file to your own script.
A .stignore file placed in the folder root excludes files with glob patterns, supporting wildcards, character ranges, negated rules and case-insensitive matching. This keeps build artefacts, caches and temporary files out of the cluster without removing them from the local disk, which cuts scan time and bandwidth on large projects.
The built-in web interface on localhost:8384 shows folder state, transfer rates, connected devices and recent changes, and manages configuration without editing files by hand. A documented REST API exposes the same information and actions, so scripts and monitoring tools can automate folder setup, health checks and alerts.
A folder can be shared with a device that stores only encrypted data, unlocked by an encryption password kept on the trusted side. This lets you park a replica on hardware you do not fully control, such as a rented server or a colleague's machine, without exposing readable file contents.
No. Syncthing has no central storage. Files travel directly between devices that you paired by exchanging device IDs. Public discovery and relay services only help devices find each other or pass traffic along; they cannot read the encrypted connection, and no copy of your data is kept elsewhere.
Syncthing cannot merge two conflicting edits, so it keeps one version as the current file and saves the other as a conflict copy whose name includes the device name and a timestamp. You review both, keep the one you want, and delete the other; every device then converges on the same result.
Yes. Devices announce their addresses to public discovery servers so they can be found, and if a direct connection is impossible, traffic can be routed through community relays. Relayed connections remain encrypted end to end, though they are usually slower than a direct TCP or QUIC link between the two machines.
In a default send-and-receive folder, yes, deletions propagate like any other change. To prevent that, mark the folder send-only on the machine holding the source, enable file versioning so replaced or deleted files received from other devices are archived, or exclude the path with ignore patterns.
It works well as a replication layer for folders that exist on both sides, particularly with versioning enabled on the destination so overwritten files are retained. Keep in mind that it mirrors deletions, so it complements rather than replaces a backup system built around long-term historical snapshots.
No account, email address or payment is required. You install the program on each machine, pair devices by exchanging device IDs, and choose which folders to share from the local web interface. Licences and quotas do not exist, and the same setup serves a two-laptop household or a larger group of machines.
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