Syncthing vs. Dropbox vs. BitTorrent Sync

Syncthing, Dropbox, and BitTorrent Sync (now Resilio Sync) are all file-synchronization tools, but they differ fundamentally in how they handle your data. Syncthing is a free, open-source, peer-to-peer sync tool that runs on your own devices with no central server; Dropbox is a cloud-based service that stores your files on its servers; and BitTorrent Sync (Resilio Sync) is a proprietary peer-to-peer tool that also avoids the cloud but is not open source. This article compares the three so you can decide which fits your privacy, cost, and convenience needs.

Background: How Each Tool Evolved

Dropbox launched in 2008 and popularized cloud file sync: you put a file in a folder, it uploads to Dropbox’s servers, and then syncs to your other devices. It made file sharing easy for non-technical users and became the default for many. BitTorrent Sync appeared in 2013 as a way to sync folders directly between devices using the BitTorrent protocol, without any cloud storage. It was later renamed Resilio Sync when the company split off. Syncthing was also released in 2013 as a free, open-source response to BitTorrent Sync’s proprietary nature. It uses a similar peer-to-peer model but is developed openly, with no company controlling the protocol or the code.

How Syncthing Works

Syncthing runs as a background program on each device you want to sync. You install it on your computers, phones, or NAS devices, and then pair them by exchanging device IDs (a long string of characters). Once paired, you choose which folders to share between which devices. Syncthing then connects directly between devices over the internet or local network, encrypting traffic with TLS. It does not store your files anywhere else—if two devices are both online, they sync directly; if one is offline, the other waits until it returns. You can add relays or global discovery servers to help devices find each other, but those servers only see encrypted metadata, not your file contents.

How Dropbox Works

Dropbox is a cloud storage service. You install its client on your devices, and it syncs a designated folder to Dropbox’s servers. Files you add are uploaded to the cloud, and then pushed down to your other devices. Dropbox keeps a copy of everything on its servers, so you can access files from any web browser or mobile app even if your own devices are off. It offers version history, file recovery, and easy sharing links. The trade-off is that Dropbox employees (or anyone who gains access to your account) can read your files, and the service costs money once you exceed the free storage quota (typically 2 GB free, with paid plans for more).

How BitTorrent Sync / Resilio Sync Works

Resilio Sync (formerly BitTorrent Sync) works similarly to Syncthing: it syncs folders directly between devices using a peer-to-peer protocol. You install the app, create a shared folder, and share a read-only or read-write key with other devices. The key grants access to that specific folder. Resilio Sync also uses encryption in transit and does not store your files on a central server. However, unlike Syncthing, Resilio Sync is proprietary software—the source code is not public, and the company offers paid tiers with extra features like selective sync and advanced sharing controls. The free version is limited to a certain number of folders or devices.

Comparing Privacy and Security

If your main concern is privacy, Syncthing is the strongest choice because it is open source and has no cloud storage. Your files never leave your devices except to go directly to other devices you control. Dropbox, by contrast, stores your files on its servers, so you are trusting Dropbox with your data. Resilio Sync is also peer-to-peer, so files do not go to a central server, but the code is closed, so you cannot verify exactly what it does. For sensitive data, Syncthing’s open-source nature is a clear advantage—security researchers can audit the code, and you can even build it yourself.

Ease of Use and Setup

Dropbox is the easiest to set up: install, sign in, and you’re done. It handles all the technical details automatically. Syncthing requires more effort: you need to install it on each device, exchange device IDs, and configure folder sharing. It also needs ports to be open or relays to work reliably. Resilio Sync is somewhere in between—easier than Syncthing but still requires key sharing and some configuration. For non-technical users, Dropbox is the clear winner. For tinkerers and privacy advocates, Syncthing’s learning curve is acceptable.

Cost and Limitations

Dropbox has a free tier (2 GB) and paid plans for more storage. Syncthing is completely free and unlimited—you only need enough storage on your own devices. Resilio Sync has a free tier that limits the number of folders you can sync (typically one or two) and paid Pro plans for unlimited folders and extra features. If you have a lot of data and don’t want to pay monthly fees, Syncthing is the most cost-effective. However, you must provide all the storage space yourself, so if you don’t have large hard drives, cloud storage might be more practical.

Common Problems and Misconceptions

A common misconception is that Syncthing is like Dropbox but without the cloud. In practice, Syncthing does not keep a history of deleted files unless you enable versioning, and it does not have a web interface for accessing files from any browser. Another issue is that Syncthing can be slower to sync if your devices are behind strict firewalls, because it has to use relay servers. Resilio Sync has similar peer-to-peer limitations. Dropbox, by contrast, syncs quickly because it uses its own CDN. Also, note that “BitTorrent Sync� is now called Resilio Sync—if you search for the old name, you may find outdated information.

How to Choose

• Choose Dropbox if you want simplicity, cross-platform access from any browser, and don’t mind trusting a company with your files or paying for storage.
• Choose Syncthing if you want free, open-source, private sync between your own devices, and you’re comfortable with some technical setup.
• Choose Resilio Sync if you want peer-to-peer sync with a more polished interface and are okay with closed-source software and possible paid tiers.

For most people, the decision comes down to privacy vs. convenience. If you need to access files from anywhere, Dropbox is hard to beat. If you want to keep your data entirely under your control, Syncthing is the best option. Resilio Sync is a middle ground, but its closed-source nature may be a dealbreaker for privacy purists.

Frequently Asked Questions

Is Syncthing really free?

Yes, Syncthing is free and open-source software, released under the MPL 2.0 license. There are no paid tiers or hidden costs. You only pay for the hardware and storage you use.

Can I use Syncthing to sync with someone else’s device?

Yes, you can share a folder with any other Syncthing device by exchanging device IDs and folder sharing settings. This is useful for collaborating with friends or family, but remember that the other person will have full access to that folder’s contents.

Does Dropbox have a peer-to-peer mode?

No, Dropbox is entirely cloud-based. It does not use peer-to-peer transfer between your devices; all data goes through Dropbox’s servers.

Is Resilio Sync the same as BitTorrent Sync?

Yes, Resilio Sync was formerly called BitTorrent Sync. The name changed in 2016 after the company rebranded. The software is still peer-to-peer, but the company now focuses on business solutions as well as personal use.

Which is faster: Syncthing or Dropbox?

Speed depends on your network and the size of files. Dropbox often feels faster for small changes because it uses a global CDN and has optimized sync algorithms. Syncthing can be just as fast on a LAN, but over the internet it may be slower if it has to use relay servers due to NAT issues.

Can I sync my phone with Syncthing?

Yes, Syncthing has Android and iOS apps. The Android app is mature, while the iOS app is available but has some limitations due to iOS restrictions. You can sync folders between your phone and computer, but note that iOS apps cannot run in the background indefinitely.

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