On the same network

No server

Two computers on the same network find each other over mDNS, exchange connection details directly, and open an encrypted direct connection. No server, and no computer that has to stay on.

• Found automatically. Each computer announces itself on the LAN over mDNS, with only an anonymous token that changes daily, so nobody can tell whose computer it is. Its name is added only while Search nearby is open.
• Direct. Content goes straight between the two computers, at the speed of your network.
• Same security. You compare two fingerprint lines when pairing, and every message after that is signed, so others on the network can't pose as your device.

Before you start

The same network

Both computers behind the same router; Wi‑Fi and wired can mix. Guest networks and Wi‑Fi with client isolation keep devices apart, and in many offices wired and Wi‑Fi are separate subnets: see different subnets below.

Windows Firewall

On first run, Windows asks whether CopySync may get through the firewall; allow it. If you clicked Cancel, click Allow under Settings → Local network in CopySync, which asks for administrator approval once.

Local Network on macOS

From macOS 15, the first time it reaches a device on your network, macOS asks whether CopySync Daemon may find devices on your local network; allow it. If you declined, turn it on in System Settings → Privacy & Security → Local Network.

No server address

Leave the server field in Settings empty. To sync across networks later, add a server or use Tailscale; paired devices stay paired.

Step 1

Pair your computers

Pair each two computers once. If the app isn't installed yet, see the quick start.

1. On one computer, open Devices and click Add device. It shows a 6-character code, valid for 5 minutes.
2. On the other, click Add device too, switch to Enter a code, type it in and click Continue.
3. Both screens show the same two fingerprint lines. Check them character by character, then confirm. Copying syncs from now on.

Without a code: Search nearby

1. On both computers, open Devices and click Search nearby. Only while this window is open can devices on the network see this computer's name.
2. When the other one shows up on the radar, click it. Both screens show the same two fingerprint lines; check them, then confirm on each.
3. This works within one subnet only. If the other computer doesn't show up, use a pairing code as above.

Step 2

Different subnets

Local discovery only reaches one subnet. When your computers are on different subnets that can still reach each other, as in many offices, you enter one address when pairing.

1. The computer showing the code lists its address below it, such as 192.168.1.20.
2. On the computer entering the code, click On a different subnet?, enter that address, and click Continue.
3. After pairing, each computer remembers the other's address. If one changes address, the other finds it again on its own; if both change, open the device's … menu under Devices and choose Enter its address.

If the subnets can't reach each other at all, such as a guest network kept apart from the office network, traffic has to go through a computer both can reach: see run a server on your LAN.

Questions