Two different problems wearing the same label

“File sync” gets used loosely, but Nextcloud and Syncthing aren’t really solving the same problem.

Nextcloud is a client-server model, same shape as Dropbox or Google Drive. One central server holds the canonical copy of every file, and every device (desktop client, phone app, web browser) syncs against that one server. The server is a real hub: it’s also where sharing links, collaborative document editing, calendar/contacts sync, and a whole app ecosystem live. If the server’s down, you can still work off your local synced copy, but nothing new syncs and nobody else gets access until it’s back.

Syncthing has no server at all. It’s peer-to-peer, every device running it talks directly to every other device running it, and they negotiate which files changed and push the differences around. There’s no central point of failure and no central point of access, either, which means no web UI to share a file with someone who doesn’t have Syncthing installed, no “log in from a browser and grab a file,” none of that. It just keeps a folder identical across every device you’ve told it to sync.

That difference drives basically every other decision below.

What you actually get with each

Nextcloud gives you a real personal cloud: a web interface you can log into from any browser, public share links with expiration dates and passwords, a mobile app with automatic photo backup, real-time collaborative editing on documents and spreadsheets (via Nextcloud Office/Collabora), calendar and contacts sync (CalDAV/CardDAV) that replaces Google Calendar and Google Contacts too, and a large app store covering things like a password manager, a Kanban board, even basic email. It’s genuinely a Google/Microsoft account replacement, not just a Drive replacement, if you’re willing to run the full stack.

Syncthing gives you exactly one thing, done extremely well: folders that stay identical across every machine you point it at, with no cloud in the middle. No web UI for outside access, no sharing links, no mobile photo auto-backup in the polished sense Nextcloud has (there’s an Android app that can sync a camera folder, but it’s sync, not a gallery app with albums and thumbnails). What you do get is genuinely superior sync mechanics for the core job: block-level delta sync (only the changed parts of a file transfer, not the whole file), fully end-to-end encrypted transport by design, and sync that keeps working on a local network even with no internet connection at all, since two devices on the same LAN just talk to each other directly.

Resource footprint, and why it matters more than people expect

This is where the gap is bigger than most comparisons let on. Nextcloud is a full LAMP-style (or now increasingly Docker/FPM-based) web application: PHP, a database (MySQL/MariaDB or Postgres), a web server, a cron job for background tasks, and usually Redis for caching if you want it to feel responsive with more than a couple of users. Realistic minimum for a smooth single-user setup is in the 1-2GB RAM range, and it grows from there as you add apps, users, or lean on the Office/Collabora integration, which is its own separate, heavier container.

Syncthing is a single static binary with no database and no web server dependency (it has a built-in minimal config UI, but that’s it). It runs comfortably on a Raspberry Pi, an old NAS, or a spare LXC with a couple hundred MB of RAM, and idles at close to nothing when nothing’s actively syncing. If your homelab hardware is already tight, that difference alone can decide this.

Security model: different threats, different guarantees

Nextcloud’s files at rest on the server are only as encrypted as you configure them to be (server-side encryption is available but adds real overhead and complexity, and most self-hosted instances run without it). What you’re protecting instead is the server itself, behind your reverse proxy, behind SSO if you’ve got it (see the Authentik/Authelia guide on this site if you don’t yet), on HTTPS with a real certificate, not exposed with default credentials. It’s the same threat model as any self-hosted web app: harden the server, and the data on it is as safe as that server is.

Syncthing is end-to-end encrypted in transit between every pair of devices, and devices only trust each other by manually-exchanged device IDs, there’s no account/password model to compromise at all, and no server to breach because there isn’t one. The tradeoff is that this same design means there’s no “recover from a lost device” story the way a cloud server gives you. If your only two devices both die at once, Syncthing has nothing left to restore from, unless one of your synced nodes is a NAS or server that’s effectively always on and backed up separately, which is exactly how most homelab users actually run it.

Where they genuinely overlap, and where one clearly wins

Both can absolutely do “keep my laptop and my NAS in sync.” Both can run inside Docker on the same host without much trouble. Past that basic case, though, the use cases diverge fast.

Nextcloud wins outright if you want: a browser-accessible personal cloud you can log into from any device without installing anything, share links to send a large file to someone who isn’t running your self-hosted stack, phone photo backup with an actual gallery view, or calendar/contacts sync to get off Google entirely. It’s also the better fit if multiple people (family, roommates) need their own accounts and permissions on a shared server.

Syncthing wins outright if what you actually want is Dropbox-style “this folder is identical everywhere” behavior with the lightest possible footprint, the strongest privacy model (nothing ever touches a server you didn’t put there, including your own, since there isn’t one), and reliable LAN-speed sync that doesn’t care whether your internet is up. It’s also a genuinely good fit as a feeder into a bigger backup strategy, syncing a working folder across a laptop and a NAS, with the NAS then getting picked up by your real backup job (see the Restic/Borg guide on this site), rather than trying to be the backup itself.

Running both isn’t unusual

A fair number of homelab setups run both, for different jobs, rather than picking one and forcing everything through it. Syncthing handles the “keep my active working folders identical across my laptop, desktop, and NAS” job, invisibly, in the background, no login required. Nextcloud sits on top as the actual cloud-replacement layer, phone backup, calendar, sharing links, the things that genuinely need a server and a web interface. They’re not competing for the same job once you see them this way, they’re solving two different problems that both happen to get called “file sync.”

Bottom line

If the question is “which one replaces Dropbox,” the honest answer is that it depends on what you actually used Dropbox for. If it was mostly “share a link to a file with someone” and “get to my stuff from a browser,” Nextcloud is the real replacement and worth the heavier footprint. If it was mostly “keep this folder the same on my laptop and my desktop” with nothing fancier than that, Syncthing does that job better, lighter, and more privately, and you’ll wonder why you ever ran a whole server for it. Don’t feel obligated to pick just one, they solve different enough problems that running both, each doing the part it’s actually good at, is a completely normal homelab setup.