Is FolderSync Safe? Privacy & Open Source Facts
Yes, FolderSync is generally safe. It is made by Tacit Dynamics, a Danish company, has over a million Google Play downloads, and stores your accounts and settings locally — files go straight to the cloud or server you configure, not through FolderSync's servers. It offers optional client-side encryption. It is not open source, and it collects anonymous crash and usage data, which you can switch off.
Any app that can read your folders and log into your cloud accounts deserves a second look before you trust it. FolderSync asks for both, so "is FolderSync safe?" is a reasonable question.
Here is what its documentation, privacy policy, and Google Play listing say as of October 2026 — and where the trade-offs are.
Who makes FolderSync?
FolderSync is developed by Tacit Dynamics ApS, a company registered in Aarhus, Denmark. It has been on Google Play for over a decade, has more than 1 million downloads, and holds a 4.4-star rating from tens of thousands of reviews.
Longevity is not proof of safety, but a long-lived, identifiable company with a real address is a better starting point than an anonymous app.
Do your files pass through FolderSync's servers?
No. FolderSync's privacy documentation says the app connects and syncs directly to the provider or server you configure. Your account credentials, folder pairs, and sync logs are stored locally in the app's database on your device.
That means your files' privacy depends mostly on where you send them. Syncing to an SMB share on your own NAS keeps everything at home. Syncing to Google Drive or Dropbox puts your files under that provider's policies.
What data does FolderSync collect?
FolderSync uses Sentry, Firebase Crashlytics (Android), and Aptabase (Desktop) for crash reports and anonymous usage statistics. That covers things like OS version, app version, device language, and basic events such as a sync completing.
The company states that reports exclude personally identifiable information like your email, IP address, or device ID, and that it does not sell or share data. You can turn analytics off in settings. On Google Play, the developer declares no data shared with third parties and data encrypted in transit.
How does FolderSync's encryption work?
| Layer | What FolderSync does |
|---|---|
| In transit | Uses the secure connection each provider or protocol supports (HTTPS, SFTP, FTPS, SMB3) |
| Optional client-side encryption | ChaCha20-Poly1305, 256-bit keys, Argon2id password derivation |
| What gets encrypted | File names and file contents, before they leave the device |
| Key storage | Your password never leaves the device |
| Limitation | Only works with one-way sync |
Client-side encryption is a genuine strength: even your cloud provider cannot read files encrypted this way. The one-way limitation matters, though. If you rely on two-way sync, those files are not covered.
Is FolderSync open source?
No. FolderSync is proprietary and distributed under an end-user license agreement, so its code cannot be independently audited.
If open source is a hard requirement, look at Syncthing for device-to-device sync, or Round Sync, an open-source Android app built on rclone that syncs folders with cloud providers much like FolderSync does. We compare these and more in 7 FolderSync alternatives.
So is FolderSync safe to use?
For most people, yes. It is maintained by an identifiable company, it does not route your files through its own servers, it keeps settings on your device, and it offers real client-side encryption.
The honest caveats are that it is closed source, it collects anonymous diagnostics by default, and your privacy is ultimately only as strong as the cloud account at the other end.
What if you would rather skip the cloud account entirely?
Some people ask about FolderSync's safety because what they really want is to stop handing their files to a third-party storage provider just to move them between their own devices.
Relaaay takes that route. You link a folder on each device, and when your devices share a network, files go directly between them. When they are apart, files travel encrypted in transit and the temporary copy expires automatically instead of living in a storage account. Relaaay is not end-to-end encrypted, and it is not open source either — but it removes the permanent cloud copy from the picture.