Syncthing

A little bit of history

Back in the mid-2000s, I remember copying files between my desktop and my laptop using a USB stick. Every time I changed something on one machine, I had to remember to copy it back to the other. I lost documents this way more times than I care to admit - I would edit a report on the laptop, forget to copy it over and then open the old version on the desktop the next morning. Panic, searching, swearing then feeling useless.

I don’t know if I can avoid being subjective here but "oh boy" Syncthing managed to make me feel some butterflies in my stomach again. It reminded me of the good things in life that are free and hit you when you expect them least.

Allow me to explain. I’ve spent decades on Windows. Like everyone else I knew a thing or two about where everything was. Moving to macOS recently felt like I landed in a country with no friends and no specific instructions.

One thing that macOS always felt behind on was the lack of certain apps. Most of the free software was designed for Windows and the macOS ecosystem for years was very small. I am happy that now I can write about a free tool that is available for both Windows and macOS users.

The author

Jakob Borg (he goes by "calmh" in the Syncthing forums) started Syncthing back in 2013 as a response to the Edward Snowden revelations about mass surveillance. The idea was simple - people should not have to trust a central server to sync their own files. The project stayed in beta for five years and reached version 1.0 only in 2019. That tells you something about how seriously the developers take reliability. Jakob lives in Sweden (like many other cool guys such as Mark Straver the creator of Pale Moon) and the Syncthing Foundation runs the project. The foundation also sits in Sweden as a non-profit. Donations from users fund the discovery servers and relay infrastructure.

The latest stable version at the time of this review is 2.0.15 released on 3 March 2026. Similar to KeePass, FreeFileSync and many other apps I reviewed on dAppCDN - Syncthing puts user control and privacy above everything else.

What Is Syncthing

Syncthing is a continuous file synchronisation program. Translation: you install it on two or more devices, tell it which folders you want to keep in sync and it takes care of the rest. Change a file on device A and a few seconds later it shows up on device B. Delete something on B and it disappears from A. Add a new folder on C and it appears on A and B too (if you allow it).

The big difference from Dropbox, Google Drive or OneDrive is simple - there is no central server in the middle. No company storing your files. No "we value your privacy" page that secretly changes every six months (special thanks to the greedy corporations that does it - I just had a discussion with a good friend yesterday). Your devices talk directly to each other using a protocol called BEP (Block Exchange Protocol) over encrypted connections. Nobody else ever sees the data.

Syncthing - a real life example

So, I ordered a secondary MacBook, a lighter machine that would allow me to travel and I was looking for a way to synchronise files and folders. If you look up for this, you will notice that the most recommended solution is to use iCloud which is nice and simple and it may work for many people but not for me and here’s why:

I like to keep my files private. I am not comfortable knowing that my files are being uploaded to a third party. Yes, I am aware of the "Advanced Data Protection" feature but still there are no absolute guarantees. I’ve seen so many security issues over the time that I lost my confidence. Simply put there is no absolute safe solution.

Maybe I don’t want to pay or I cannot afford to pay over a certain amount of money. The iCloud is nice at this time it has an option to pay 1 EUR for like 50 GB per month. It is a good price if you’re dealing with small files but that’s another discussion. The prices are reasonable and there is value in it but that depends on each case and it is not for me. I wanted all the data to be transferred locally as it is much safer and also faster.

I wanted both a backup and a synchronising solution.

After doing my research I opted for Syncthing and I will describe the entire process.

First, I backed up all of my data from my primary laptop. If you’re using Mac the easiest way is to use the "Time Machine" feature - you just plug an external drive in your Mac and backup everything. In Windows there are many ways to do it but the easiest way is to copy the data from your laptop to an external drive (SSD or HDD).

Once I backed up my data - I installed the new MacBook and opted to install it from this backup so I can get all the files directly from the backup - why copy them twice since you’re installing a new macOS from scratch.

After the installation finished I had two laptops with the same files but from now on I wanted them to be in sync without having to copy files to an external drive or send them via other methods. The purpose is simple: privacy and easy to have the same data and most important to resume my work each time and not waste any more time - the backup in this case I see it as a great bonus.

Install Syncthing

Step 1. First, install it on the first machine (laptop or desktop). The setup process is different depending on your operating system:

For macOS - drag the downloaded archive or the .dmg file in your Application folder. Go to Apps then right-click and "Open". But macOS might not like it that you’re using a 3rd party app so you need to go to: System Settings > Privacy & Security > Full Disk Access and make sure the button next to Syncthing is set on "ON".

For Windows - the setup is standard and easier.

Step 2. As soon as the browser interface will open, usually the standard address is this one http://127.0.0.1:8384. You will notice an alert that warns you about a missing password. That is normal - click on "Actions" - "Settings" then go to "GUI" tab. Now set up an username and a password - in those two subfields "GUI Authentication User" and "GUI Authentication Password". Make sure to also check the "Use HTTPS for GUI". Then make sure to click "Save".

Step 3. Repeat the whole process on your secondary machine/laptop - of course on your secondary machine - choose a different username and a password.

Optional note: If you’re frustrated with so many usernames and passwords - please don’t be - there are so many tools and apps to save your passwords. Just use a password manager such as KeePass or Password Safe (both of them are available on dAppCDN and we are an official mirror for both) or even Google Password Manager.

Now, if you installed your secondary device - you have Syncthing running on both machines so let’s make them know about each other so they can "talk" between them.

Go on your first machine (the primary one) and in Syncthing interface go to "Actions" and then choose "Show ID". A new window will pop-up with a long code and a QR code. Leave this window open.

Go on your secondary machine and look down to "Remote Devices" section and click on "Add Remote Device". If your both devices are in the same room - they should already see each other but otherwise copy that long code and put it here. Just add a name (e.g. my secondary device) and hit "Save".

Go back to your first device and you should see a notification "Device X wants to connect". Click on "Add device". That’s it! If you look on the other device you should see the green status "Connected". Right-now these two devices are "talking" between them BUT they are NOT transferring any files. To give you an analogy - you just met someone, you guys exchanged your phone numbers but you didn’t exchange anything, for example, no SMS or no pictures over WhatsApp or Telegram or Instagram or whatever app you guys are using.

Important: You will see some terminal (black windows) opening - DO NOT CLOSE them - just minimize and ignore them. Step 4. Let’s start using Syncthing - I will tell you what I did.

So, I am quite disorganized - plenty of folders, inside of them - a lot of files. After I spent 2 days working on arranging things I was left out with 40 folders full of files. I decided to create a single Folder named "2026" - you can name it whatever you like and here I moved all those 40 folders.

Then, I returned to Syncthing interface and from the "Folders" section - I clicked on "Add Folder" and added my folder named "2026" (again, you can choose any name you like). I entered the path to it. If you don’t know the path - don’t worry:

For Windows - perform a right-click on it - then - select "Copy as path" or CTRL+SHIFT+C - then return to Syncthing and paste the path - with your mouse - Paste or with your keyboard "CTRL+V".

For macOS - Go to "Finder" - perform a right-click on your folder. Hold the keyboard button "Option". You will notice that the option Copy "Folder Name" becomes Copy "Folder Name" as Pathname. Click on it - then return to Syncthing and paste it or with your keyboard "CTRL+V".

Important: If you are receiving an error such as "Permission Denied" after you added the path, it means that you forgot to activate the "Full Disk Access" in your macOS.

Once again, (this is not mandatory) repeat the same steps on the other device. To make it easier - I kept everything on the other device - they are identical - same folder name, same files etc. If you don’t do this on the second device, Syncthing will ask you (that’s why I said it is optional).

Once you hit "Save" you should see the status changing from "Unknown" into "Syncing". You can run a test - just copy a random file on your folder and you should see it appear after 30 seconds - 1 minute on the other device as well.

Security first!

I recommend you (I’m a bit paranoid) the following settings:

Settings - General:

Under "Automatic upgrades" section I like to keep it "No upgrades" - Please make sure to check it more often though. This is a double-edge sword - it keeps you safe in the highly unlikely event that the Syncthing project or servers are compromised somehow (example: Notepad Plus Plus incident). At the same time, if there is a critical bug - you want to get the update as fast as possible but I take my chances considering I am applying several security settings. Anyhow - please make sure you do check for the latest version - at least once a month.

Settings - GUI:

Make sure that "Use HTTPS for GUI" is selected. Make sure that the GUI password is a strong one. The best practices also recommend to change it at least once a year - but that is a general security recommendation, not just for this app.

Settings - Connections: Under Sync Protocol Listen Addresses I like to use this (it forces Syncthing to use only the standard protocol transfer): tcp://0.0.0.0:22000

I don’t leave in a vacation and keep my desktop or primary device open - I like to shut it down - if you’re like me, make sure to check only two things: Enable NAT traversal and Local Discovery. UNCHECK all the other three options. Hit "SAVE" if you apply these changes.

Folders

Click on "Edit" field and visit these sections:

File Versioning - my choice would be "Staggered File Versioning" and I like to select Maximum Age - 30 days - just in case I delete something by mistake.

Ignore Patterns - if you’re using macOS I recommend you to add the following lines there: .DS_Store .stversions .Spotlight-V100 .Trashes

These will prevent the synchronisation of some hidden files that might cause potential conflicts or it could leak details about how you organize your files. Make sure to click SAVE.

Other security

I like to deactivate the UPnP feature in my home router - Syncthing doesn’t need this feature.

The database headache and version 2.0

The old database engine drove me crazy for a long time. They used LevelDB for the file index and it was fine until you pushed massive folders. I know folks running 50TB storage arrays and LevelDB would just choke. We all hated the "99% stuck" error. You'd watch a transfer hit 99% and then freeze. For hours. Tracking block states in that old database format was a complete mess.

August 2025 changed everything. Version 2.0 ripped out LevelDB and dropped SQLite in its place. You probably know SQLite - it runs inside almost every phone and browser on the planet. The stability improvement is massive. You get actual transactions and foreign keys now. That annoying stuck bug? Completely dead. Plus if the database breaks you can open it with a standard SQLite reader and see what broke.

The Untrusted Device Feature - Your Own Zero-Knowledge Cloud

This is my favourite feature in Syncthing and I think it is underused. Let's say you want an offsite backup of your files. You could use Dropbox or Google Drive but then Google reads your files (yes, they do - it is in their terms of service). You could rent a VPS and install Syncthing on it but what if the VPS provider snoops around?

The untrusted device feature solves this. You set up Syncthing on a cheap 5 EUR per month VPS. When you share a folder with this VPS, you mark it as "encrypted" and set a password. Here is what happens:

On your local machine, everything is normal - you see your files, edit them, whatever. Before each block of data gets sent to the VPS, Syncthing encrypts it using XChaCha20-Poly1305. The file names get encrypted too using AES-SIV. Then the encrypted data is base32-encoded and split into a scrambled directory structure.

If the hosting provider gets nosy and checks your VPS disk, they get nothing. Just a wall of random folders named stuff like "4/IS/DQJP". The contents are scrambled. They won't see your filenames or figure out what file types you stored. Should your main hard drive die, recovery is easy enough. Install the software on a fresh PC. Type in your decryption password and pull the data down.

Smartphones ruin the fun

I hate editing files on my phone but I still need them synced. This is where things get ugly today. Google killed the official Android app. They pushed those aggressive "Scoped Storage" rules late in 2024 and kicked the software off the Play Store. Android restricts apps from touching random files now. You have to use F-Droid now to grab the "Syncthing-Fork" release. Volunteers keep it alive. It runs fine on my mobile and deals with background tasks properly on newer Android 15 and 16 builds. But don't bother searching the official Play Store. It is gone.

Then you have Apple and their locked-down sandbox. You can't run persistent background daemons on an iPhone. Unless you write an audio player or a VoIP app, iOS kills your background processes. Monitoring files over a network connection violates their strict rules. You will find Möbius Sync and Synctrain in the App Store. They wrap the core engine in an iOS interface. But they suffer from those same restrictions. You usually have to open the app yourself to force a transfer.

Finally

Dealing with two or more devices can easily make your life harder. The truth is that I discovered Syncthing recently when I needed a solution to my problem. Basically, this utility runs as a daemon and it offers an easy enough graphical interface - you can access it on any installed browser and it is using your local host address. It might look a little complicated, especially if you never used a similar tool before but you just need to pay attention for a few minutes as there are really only a few things to be checked and the setup process is pretty fast when you’re doing it again for the second device - you’re just repeating all the steps.

Once you see it running - it gives you a huge feeling of accomplishment because you own your data, the transfer is locally (private) and if you apply those security recommendations I wrote above it should be safe as well. Finally, Syncthing has been developed since 2013 - it is now a stable and mature tool and it runs on almost all operating systems. Therefore, I encourage you to consider a donation towards Syncthing.

dAppCDN Note: Version 2.1 was released by the project manager Jakob Borg (calmh) - May 12 2026 - https://forum.syncthing.net/t/syncthing-2-1-0/26698

• Devices and folders can now be grouped in the GUI by setting the new group attribute.
• HTTP and HTTPS proxies with support for CONNECT can now be used, in addition to the existing support for SOCKS proxies (the environment variable all_proxy=https://...).
• Block indexing can be turned off for folders where it’s more desirable to optimise for reduced database size and overhead than minimal transfer size (the blockIndexing attribute on folder configuration).
• GUI login session duration can be configured to be longer or shorter than the default one week, or set to infinitely long. The cookie path can also be adjusted. (The sessionCookieDurationS and sessionCookiePath attributes in the GUI configuration.)