Syncthing

Open-source file synchronization, honestly reviewed. No marketing fluff, just what you get when you run it.

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TL;DR

• What it is: Open-source (MPL-2.0) peer-to-peer file synchronization — your files move directly between your devices, never through a third-party server [website].
• Who it’s for: Privacy-conscious users, NAS owners, developers, and anyone paying for Dropbox or Google One who wants that bill to disappear. Also game players syncing save files across devices [1][4][5].
• Cost savings: Dropbox Plus runs $9.99/mo for 2TB; Google One 2TB is $9.99/mo; OneDrive comes bundled with Microsoft 365 at $6.99/mo. Syncthing is $0 — and if your devices are on the same LAN, files never leave your network at all [5].
• Key strength: Genuinely decentralized. No company in the middle. No subscription. No storage limits beyond your own hardware. 80,909 GitHub stars and over a decade of active development [profile].
• Key weakness: The setup experience is rough for non-technical users. There’s no setup wizard, the web UI is utilitarian at best, and iOS support is limited to a third-party paid app after a free trial threshold [5].

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What is Syncthing

Syncthing is a continuous file synchronization program. You install it on two or more devices, pair them together, designate shared folders, and it keeps those folders identical across all devices — automatically, in real time [website].

What makes it structurally different from every mainstream cloud storage service is that there is no central server. Files move peer-to-peer: directly from your laptop to your NAS, from your desktop to your Steam Deck, from your phone to your home server. If those devices are on the same WiFi network, the data never touches the internet at all [5][website]. If they’re remote, Syncthing can connect them through its relay infrastructure — but the relay only forwards encrypted traffic and cannot read your files [website].

The project describes itself plainly in its README: “Open Source Continuous File Synchronization.” Its stated priorities, in order, are data safety, security against attackers, ease of use, automation, and universal availability [README]. That ordering matters — this is a project that chose correctness and safety over flashy features.

The license is MPL-2.0 (Mozilla Public License 2.0), which is more permissive than GPL but requires that modifications to Syncthing’s own source files be shared back. It does not restrict you from using Syncthing in commercial environments or pairing it with proprietary software [profile]. Commercial support is available through Kastelo, which also sponsors the project’s development [website].

As of this review the project sits at 80,909 GitHub stars — an unusually high number that reflects over a decade of sustained community trust rather than a recent growth spike.

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Why people choose it over Dropbox, Google Drive, and OneDrive

The five sources we synthesized tell a consistent story: Syncthing wins on privacy, cost, and flexibility, and loses on ease of setup and mobile experience.

The privacy argument is structural, not just a feature checkbox. The PCWorld review [5] makes this clearest: with cloud storage services, “files sync through a company’s servers, which creates points of surveillance and vulnerability.” With Syncthing, “if all those devices are on the same network, your files never leave that network.” This isn’t a privacy mode you enable — it’s the default architecture. There’s no company that can be subpoenaed, hacked, acquired, or that can change its terms of service to scan your files.

The XDA Developers piece [1] documents a user running Syncthing between a PC, Mac, NAS, and other devices — with Proxmox Backup Server, Kopia, and TrueNAS Scale also in the stack. The motivation was a painful lesson: game saves lost during an OS reinstall because Steam Cloud failed and the manual backup was a month stale. Syncthing with file versioning enabled would have caught it. That’s the recurring pattern in user testimonials: people who got burned by cloud storage gaps (sync conflicts, storage limits, privacy concerns, subscription price hikes) and wanted something they controlled entirely.

The no-central-server design also means no storage caps. Dropbox charges you based on how much data you store on their infrastructure. Syncthing doesn’t store anything anywhere — it just keeps your own devices in sync. Whether you’re syncing 10GB of documents or 4TB of video archives, the software cost is identical: $0.

The flexibility gap versus cloud storage is real. PCWorld [5] enumerates use cases that mainstream cloud storage handles poorly or not at all: syncing game saves that live in protected system directories, pushing files to devices you’d rather not connect to cloud storage (a Steam Deck being the example), one-way sync from one drive to another, and sharing large video or audio files quickly without consuming anyone’s cloud quota. Syncthing’s granular control — per-folder sync direction (send-only, receive-only, send-receive), per-folder versioning, per-device bandwidth throttling — is simply not available on Dropbox or Google Drive [5].

The honest tradeoff: all of this comes at a steeper setup cost. PCWorld [5] says outright: “Syncthing isn’t the easiest to set up. Its interface is unintuitive, and even figuring out what to install can lead to confusion.” This isn’t a project that holds your hand.

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Features

Core sync engine:

• Continuous bidirectional sync; changes propagate automatically without manual intervention [website][README]
• Configurable sync modes per folder: Send & Receive, Send Only, Receive Only [5]
• File versioning with configurable retention — keeps old versions of modified or deleted files [1][5]
• Delta sync — only changed portions of files are transferred, not the whole file [5]
• Works over LAN (fast, data stays local) and over the internet via relay [5][website]
• Device pairing via cryptographic device IDs — no usernames, no passwords between devices [website]
• UPnP support for NAT traversal; relay fallback when direct connection isn’t possible [website]

Security:

• All traffic encrypted with TLS, including perfect forward secrecy [website]
• Every device identified by a strong cryptographic certificate [website]
• Global discovery and relay can be disabled entirely for air-gapped LAN-only setups [3]
• GPG-signed release binaries; macOS and Windows builds are code-signed [README]

Platform support:

• Windows, macOS, Linux, FreeBSD, Solaris, OpenBSD [website]
• Android app available via Google Play and F-Droid [3][5]
• iOS: only Möbius Sync, a third-party app, free up to 20MB then $5 — and it cannot sync the iOS Camera Roll [5]
• NAS integration: native app store packages for TrueNAS Scale, Unraid, Synology DSM, TerraMaster TOS [1]
• Steam Deck: installable via Discover app using syncthing-gtk [4][5]

Ease of use (honest assessment):

• Web-based GUI runs on localhost:8384; accessible from any browser on the local network [2]
• No setup wizard — you manually exchange device IDs and accept folder share requests [2][5]
• Third-party wrappers add system tray icons, startup behavior, and notifications: SyncTrazor (Windows), SyncThing-MacOS, SyncThing-GTK (Linux/Steam Deck) [5]
• Initial pairing requires both devices to be online simultaneously [2]

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Pricing: SaaS vs self-hosted math

Syncthing is free. The software costs nothing regardless of how many devices, folders, or gigabytes you use [profile][README].

Cloud storage for comparison:

• Dropbox Plus: $9.99/mo (2TB)
• Dropbox Essentials (business): $16.58/mo
• Google One 2TB: $9.99/mo
• OneDrive 1TB (Microsoft 365 Personal): $6.99/mo
• iCloud+ 2TB: $9.99/mo

Self-hosted with Syncthing:

• Syncthing software: $0
• If syncing only between devices you already own: $0/month ongoing
• If you want a always-on sync node (so your laptop syncs even when your desktop is off): a $5–6/mo VPS or a NAS you already have

Concrete scenario: a person syncing documents, photos, and game saves across a laptop, desktop, and NAS — currently on Dropbox Plus. Annual Dropbox cost: $119.88/year. With Syncthing between owned devices using an existing NAS: $0/year. Savings: $119.88/year plus whatever Dropbox was going to charge you after the next price increase.

The caveat isn’t the software — it’s the time cost of initial setup, which PCWorld [5] characterizes as “a little work.” If you’ve never set up a P2P tool, budget a couple of hours. If you’re a NAS user on TrueNAS or Unraid with the app store available, probably 20 minutes [1].

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Deployment reality check

What the setup actually looks like:

Install Syncthing on both (or all) devices. On first launch it generates encryption keys, creates a default configuration, and opens its web UI at http://127.0.0.1:8384 [2]. You find your device ID (a string like 6FOKXKK-SKUBWFW-...), share it with the other device, accept the pairing request on both sides, then share a folder — at which point Syncthing starts watching it and syncing changes automatically [2][4].

The Syncthing documentation [2] recommends doing this on both machines simultaneously. The Linux Mint forum guide [3] recommends creating a dedicated Sync folder on both devices and using it as the sync root. The Anna Plays Skyrim guide [4] documents the Mac-to-Steam-Deck flow and notes the web UI looks identical on both platforms since it’s just a local web page.

What can go sideways:

• The iOS situation is genuinely bad. If you need to sync with an iPhone, Möbius Sync is the only option, it costs money after the first 20MB transferred, and it cannot access the Camera Roll [5]. If iOS is a hard requirement, Syncthing is not the right tool.
• Firewall configuration. If you’re running UFW or another firewall on Linux, you need to allow Syncthing through it explicitly (sudo ufw allow syncthing) [3]. On Windows, the installer typically handles this.
• Syncthing ≠ backup. This is worth saying plainly because it’s the most common misunderstanding [1]: deleting a file on one device propagates the deletion to all synced devices. It keeps files identical, not safe. For backup semantics (point-in-time recovery, deleted-file retention), you need file versioning enabled per-folder, or a separate backup tool like Kopia or restic running alongside it.
• Global discovery and relays use Syncthing’s own infrastructure by default, which means your device IDs are briefly visible to Syncthing’s discovery servers when connecting remotely. For maximum privacy, disable global discovery and relay and use local discovery only — though this limits functionality to your local network [3][website].
• No system tray or startup behavior by default. The raw Syncthing binary doesn’t auto-start or show a tray icon. You need a wrapper (SyncTrazor, SyncThing-MacOS, etc.) or to configure it as a system service yourself [5].

Realistic setup time for a technically comfortable user: 20–45 minutes for the first device pair. For a non-technical user following a guide on two devices simultaneously: 1–2 hours including firewall and wrapper setup.

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Pros and Cons

Pros

• No central server, ever. Your files never transit a third-party service. This is structural, not a setting [website][5].
• Zero cost. No storage tiers, no subscription, no per-device fees [profile].
• 80,909 GitHub stars and over a decade of active development — this is not a hobby project that might disappear [profile].
• Granular per-folder control. Send-only, receive-only, full versioning, bandwidth limits — significantly more control than any mainstream cloud storage [5].
• Works on LAN without internet. Syncs at full local network speed when devices are on the same network [5].
• Broad platform support. Windows, macOS, Linux, Android, FreeBSD, NAS platforms (TrueNAS, Synology, Unraid) [1][website].
• No storage limits. Sync 100GB or 100TB — the software doesn’t care [5].
• MPL-2.0 license. Permissive enough for commercial and enterprise use without legal complexity [profile].
• Cryptographically strong identity. No username/password between devices — device certificates handle authentication [website].

Cons

• iOS support is a dead end. Möbius Sync costs money after 20MB and can’t access the Camera Roll [5]. If you have an iPhone, plan around this.
• No setup wizard. The first-time experience is documentation-first, not guided. Non-technical users will struggle [5].
• Unintuitive web UI. PCWorld [5] calls it “unintuitive” explicitly. It’s functional, not friendly. Third-party wrappers are effectively required for normal desktop use.
• Not a backup tool. Deletions propagate. Without versioning enabled, a misfire destroys the file on all devices [1].
• No selective sync in the cloud sense. You sync entire folders, not individual files on demand. More like Dropbox’s original model than modern on-demand sync.
• Remote sync requires relay or port forwarding. Without opening a port or relying on Syncthing’s relay infrastructure, remote sync doesn’t work reliably in all network configurations [3].
• No sharing with non-Syncthing users. You can’t share a link to a file. Syncthing is device-to-device only [5].

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Who should use this / who shouldn’t

Use Syncthing if:

• You’re paying $8–12/month for Dropbox, Google One, or iCloud and the primary value is file sync across your own devices (not sharing files with others).
• You have a NAS or home server and want an always-on sync node without a cloud dependency.
• You need to sync large files — video projects, game libraries, raw photo archives — where cloud storage costs or upload speeds make cloud sync impractical.
• You want your files to stay off third-party infrastructure for privacy or compliance reasons.
• You’re comfortable with a one-time technical setup or willing to pay someone to do it once.
• You’re a developer who wants to sync project files, scripts, or dotfiles across machines.
• You play games and want cross-device save sync beyond what Steam Cloud covers [1][4].

Skip it (use Nextcloud instead) if:

• You want sync plus a web interface, file sharing via link, calendar, contacts, or office document editing — Syncthing does file sync only.
• You need to share files with people who don’t have Syncthing installed.

Skip it (stay on Dropbox/Google Drive) if:

• You need to share files or collaborate with people who aren’t on your devices.
• You have an iPhone as a primary device and need photos synced — the iOS situation is genuinely broken [5].
• You’re not comfortable with any technical setup and don’t have someone to help.
• You need mobile-first access to files (Syncthing doesn’t have a conventional mobile files app experience).

Skip it (use rsync/Resilio Sync) if:

• You want one-way sync only and are comfortable with command-line tools — rsync is simpler for that specific case.
• You need commercial support with an SLA beyond what Kastelo offers.

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Alternatives worth considering

• Nextcloud — heavier, more features (file sharing, calendar, office), self-hosted with a central server you run. Better for teams; more complex to deploy and maintain than Syncthing.
• Seafile — similar to Nextcloud but faster sync performance, lighter footprint. Has a central server model unlike Syncthing’s P2P.
• Resilio Sync — commercial product with a P2P model similar to Syncthing. More polished UI, better mobile apps, includes iOS Camera Roll sync. Costs $59.99/year for Pro.
• Dropbox / Google Drive / OneDrive — the incumbents. Easiest setup, best mobile apps, best file sharing. No self-hosting option; you pay forever and your files live on their servers.
• rsync — command-line, battle-tested, one-way sync only. No real-time sync; runs on a schedule. Zero dependencies beyond SSH. Right tool for server-to-server backup flows, wrong tool for device sync.
• SyncThing-Fork — a maintained Android fork of the official Syncthing Android app, available on F-Droid, actively developed and considered by many the better Android option [3].

For the target audience — a non-technical founder or small team paying for cloud storage they use only for private file sync across their own devices — the realistic shortlist is Syncthing vs Nextcloud. Pick Syncthing if you want minimal moving parts and maximum privacy with no central server. Pick Nextcloud if you need file sharing, web access, or a broader feature set.

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Bottom line

Syncthing is the most honest file sync tool available. It doesn’t try to be a collaboration platform, a backup solution, or a cloud drive — it tries to be one thing: keep your files identical across your devices, with no third party in the middle, forever, for free. After a decade and 80,909 GitHub stars, it does that thing extremely well. The tradeoffs are real: the setup experience is rough, iOS support is genuinely limited, and non-technical users will need help getting started. But for anyone currently paying $10/month to sync files between their own devices, or anyone who simply doesn’t want their documents transiting Google’s or Dropbox’s servers, the math is obvious. One afternoon of setup — or a one-time deployment from someone who knows what they’re doing — and the bill goes to zero permanently.

If the setup is the blocker, that’s exactly what unsubbed.co’s parent studio upready.dev deploys for clients. One-time fee, done, you own the infrastructure.

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Sources

1. Ayush Pande, XDA Developers — “I self-host Syncthing to sync files between my PC, Mac, NAS, and other devices” (Jul 25, 2025). https://www.xda-developers.com/i-self-host-syncthing-to-sync-files-between-my-pc-mac-nas-and-other-devices/
2. Syncthing Documentation — “Getting Started”. https://docs.syncthing.net/intro/getting-started.html
3. Linux Mint Forums (Malsasa) — “Beginner’s Guide to Syncthing — Android & Mint File Sharing” (Dec 17, 2020). https://forums.linuxmint.com/viewtopic.php?t=337694
4. Anna Plays Skyrim — “HOWTO: Use Syncthing to sync between devices” (May 21, 2025). https://skyrim.annathepiper.org/2025/05/21/howto-use-syncthing-to-sync-between-devices/
5. Jared Newman, PCWorld — “How to use SyncThing to sync files without the cloud”. https://www.pcworld.com/article/2048298/how-to-use-syncthing-to-sync-files-without-the-cloud.html

Primary sources:

• GitHub repository and README: https://github.com/syncthing/syncthing (80,909 stars, MPL-2.0 license)
• Official website: https://syncthing.net
• Documentation: https://docs.syncthing.net
• Security page: https://syncthing.net/security/