Do you love the privacy of local-first apps but hate having your data locked to one device? Want to access your Obsidian notes or KeePassXC passwords on all your devices without using the cloud? Here’s how Syncthing makes local-first apps work like cloud apps—while keeping your data private.
What is the biggest problem with local-first apps
Local-first applications are fantastic for a lot of reasons. They keep your data completely private, since nothing you do is saved to the cloud. You don’t have to worry about sharing your data with third parties, or your information being used to train AI models. You have complete ownership and control over your data.
On top of that, these apps aren’t dependent on the internet. Even if your connection is down or slow—or if some random server is having issues—the apps keep working. As long as your computer is functioning and your hardware is capable, you can expect smooth performance.
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All that said, most local-first apps aren’t perfect, and you notice it immediately when you try to access your data from a different device. Let’s say you have Obsidian installed on your computer with all your notes stored locally. If you install Obsidian on your smartphone, you won’t be able to access any of those notes.
The same applies to KeePassXC—a robust, secure, open-source password manager. Passwords you save on one computer won’t be accessible from another system. Even worse, if something happens to that computer, and you didn’t back up your data (notes or passwords)—everything is simply gone.
Why most local-first apps skip syncing or cloud-saving functionalities
It’s not that developers of local-first apps can’t build syncing or cloud-saving features—they absolutely can. The real issue is economics.
If developers want to include cloud functionality, they need to host user data on servers—and servers cost money. However, most local-first apps are free to use, which means maintaining cloud infrastructure quickly becomes financially unsustainable.
That said, some free and local-first apps have found clever ways to work around this problem. For example, apps like Obsidian, which is free to use by default, offer cloud syncing as a paid add-on. While this is a great way to support the apps you like, it also ties you to a subscription—and not everyone is a fan of that.
A few local-first apps take a different approach by letting you use third-party cloud services to host your data, avoiding the cost of running their own servers. For example, Super Productivity—a powerful task management app—lets you store its database in Google Drive, which then syncs across devices. But this solution isn’t perfect either. Not only are you exposing your data to a third party—undermining the privacy appeal of local-first apps—but you’re also making your data dependent on external servers, outages, and service disruptions.
Some apps, like Notion, are free (or more accurately, freemium) and still manage to offer cloud infrastructure. In these cases, paid users subsidize the cost for free users. Other “free” apps offset their cloud costs by harvesting user data and selling it for profit—effectively making the user the product.
How Syncthing solves this problem
Syncthing is free and open-source software (FOSS) that establishes a peer-to-peer connection between two or more devices for data syncing. There’s no cloud service involved—the tool turns all your devices into equal peers that communicate directly with each other.
Let’s say you want to sync your Obsidian notes between a Windows PC and an Android smartphone. You install Syncthing on both devices, set up a sync folder on each, and place your Obsidian vault inside those folders. From that point on, every change you make on one device automatically syncs to the other—and vice versa.
The same approach works for your KeePassXC passwords, Super Productivity tasks, or any other local-first app data you want to keep in sync. You can also create multiple folders in Syncthing and sync each one to different devices. For example, your KeePassXC password database might sync between your desktop and laptop—but there’s no need for that data to live on your smartphone, especially since there’s no mobile app for it. Syncthing gives you complete flexibility to choose exactly which devices receive which data.
Does Syncthing work over mobile data?
Because Syncthing is free, open source, and establishes a peer-to-peer connection between devices, some people falsely assume it only works on a local network. Fortunately, the Android app—an open-source wrapper called Syncthing-Fork—works over both Wi-Fi and mobile data. This means that even if you’re outside your home and away from your computer, you can still save new notes to your Obsidian vault. When you get back home, everything syncs automatically to your computer.
That said, syncing over mobile data is disabled by default, since continuous syncing can eat through your data plan quickly if you’re not careful. Furthermore, Syncthing will resume normal syncing as soon as your phone reconnects to Wi-Fi, so it isn’t a huge concern. Still, if you want the flexibility, you can go to Settings > Run Conditions and turn on “Run on Mobile Data.”
Is Syncthing reliable for cloud backups?
Cross-device syncing isn’t the only benefit you get from cloud apps—you can also rely on them as a “backup” for your data. If something happens to one device, your data is still safe in the cloud.
Now, initially, I wasn’t sure I’d get this benefit from Syncthing. I felt that if a file got corrupted or deleted on one device, those changes would sync everywhere and compromise all of my data. Thankfully, you can prevent this from happening by using Syncthing’s built-in file versioning system.
When versioning is enabled for a synced folder, Syncthing automatically archives older versions of files whenever they’re modified or deleted due to changes coming from another device. You can choose from multiple versioning strategies and also control how many old versions are kept before they’re cleaned up.
Versioning only protects against changes coming from other devices. If you delete a file locally on your laptop, that laptop won’t keep a backup. However, when that deletion syncs to your desktop, the desktop will archive the old file in its “.stversions” folder before deleting it.
How to use Syncthing to sync your local data?
Installing and setting up Syncthing is straightforward and usually takes just a few minutes. If you want a quick walkthrough of the setup and configuration process, check out my guide on using Syncthing to sync Obsidian notes between your PC and phone. I’ve also written a separate guide that shows how I use Syncthing to sync files between my Linux and Windows PCs, which should give you a clear idea of how PC-to-PC syncing works in practice.
