Clipboard sync across different networks
Most clipboard and file-sharing tools cannot do this, and the reason is that they find each other by shouting on the local network. A broadcast does not leave the subnet, so a phone on mobile data is invisible to a laptop on home Wi-Fi no matter what you change. To sync across networks you need a tool that meets in the middle at a known address instead — which is what a browser-based clipboard does.
Why the same-Wi-Fi limit exists
AirDrop, LocalSend, KDE Connect and the original Snapdrop all work the same way underneath. When you open them, each device sends a discovery message to every address on its own network segment — mDNS, UDP broadcast or Bluetooth, depending on the tool — and listens for replies. Whatever answers, appears in the list.
That design is why they need no account and no configuration: nobody has to be told where anybody is. It is also exactly why they stop at the edge of the network. Routers do not forward broadcast traffic between subnets, so two devices on different networks never hear each other. There is nothing to fix, no port to open, no setting you have missed — it is the mechanism working as designed.
Three common situations run into it, and none of them is a fault:
- Phone on mobile data, laptop on Wi-Fi. Different networks even though the devices are touching.
- Office or campus Wi-Fi with client isolation. Devices are on one network but deliberately walled off from each other, which is a security feature on guest and corporate networks.
- Genuinely apart — home and work, or two different cities.
What works instead
The alternative is for both devices to connect outward to the same known address and be introduced there. Neither has to find the other, so it makes no difference whether they are in one room or on opposite sides of the world. The trade is that something in the middle now knows the two are talking — so the question that matters becomes what that middle can see.
| Tool | Across networks | How devices meet | System clipboard |
|---|---|---|---|
| RealtimeClipboard | Yes | Short key typed on both | Yes |
| PairDrop | Yes | 6-digit pairing code | Text arrives as a message |
| Windows clipboard sync | Yes | Microsoft account | Yes, Windows to Windows only |
| Apple Universal Clipboard | No | Bluetooth + Handoff, in range | Yes, Apple devices only |
| KDE Connect | No | Local network discovery | Yes |
| LocalSend / Snapdrop | No | Local network discovery | No |
| AirDrop | No | Bluetooth + peer-to-peer Wi-Fi | No |
The three that cross networks each ask for something in return. Windows clipboard sync wants a Microsoft account on both machines and only talks to other Windows PCs. PairDrop is account-free and cross-platform, but sends text as a message rather than putting it on your clipboard. The third route is a browser clipboard, which is what the rest of this page describes.
Syncing without an account, across any two networks
- Open the clipboard on the first device. It generates a short key.
- Type that key on the second device, or scan the QR code.
- Copy something on either device.
- Switch to the other and paste. It is already on the system clipboard.
The key is what replaces discovery. Both devices connect out to the same relay and ask for the room belonging to that key, so they find each other without either needing to know where the other is. Home Wi-Fi to mobile data, laptop to phone, work to home — all the same case.
What the server in the middle can see
This is the part worth being specific about, because "it goes through a server" is the real cost of crossing networks and it is usually left vague.
Text is encrypted in your browser with AES-GCM before it is
sent. The relay is addressed by SHA-256(key) rather than
by the key, so it can route your messages to the right room without
ever holding the key needed to read them. It keeps nothing on disk:
messages exist only long enough to be forwarded. Files skip it
entirely and go directly between the two browsers over WebRTC.
What it does see is that some room hash was busy at some time, and the IP addresses of the two connections. It is never given your key, your text, your filenames or who you are. That room hash is derived through the same 250,000-iteration stretching as the encryption key, so it cannot be worked backwards to your key cheaply — the threat model shows the numbers. The code is MIT-licensed and the relay is a small enough Python service to read in one sitting — and if you would rather not take anyone's word for it, you can run your own and point the app at it.
Worth knowing before you rely on it
- The key is the password
- Anyone who learns it can read that session while it is open. Treat it like one.
- Automatic capture needs Chromium
- Firefox and Safari can send and receive pasted text, but cannot read the clipboard on their own.
- Background reading is not possible
- No browser can read the clipboard while its tab is in the background. You switch to the tab and it picks up what you copied.
- Files are capped at 5 MB
- For anything larger, a dedicated transfer tool is the right choice.
Common questions
Can I sync my clipboard between devices on different Wi-Fi networks?
Yes, but not with tools that rely on local discovery. AirDrop, LocalSend, KDE Connect and Snapdrop all find devices by broadcasting on the local network, and that broadcast does not cross a router. A browser-based clipboard works instead by having both devices connect out to the same relay using a shared key, so the networks they are on stop mattering.
Why can't my phone see my laptop on mobile data?
Because they are on two different networks. Local discovery only reaches devices on the same network segment, and a phone on cellular is on a completely separate one from a laptop on Wi-Fi, even when the two are side by side. Turning the phone's Wi-Fi on and joining the same network fixes it for those tools; anything else needs a tool that does not rely on discovery at all.
Does clipboard sync work on guest or office Wi-Fi?
Local-discovery tools usually do not. Guest and corporate networks commonly enable client isolation, which stops devices on the same network from talking to each other directly — deliberately, as a security measure. A browser clipboard is unaffected, because each device only makes an ordinary outbound HTTPS connection rather than trying to reach the other device.
Does the server see what I copy?
No. Text is encrypted in the browser before it is sent, and the relay is addressed by a hash of your key rather than the key itself, so it can route the message without being able to decrypt it. It stores nothing on disk. Files do not pass through it at all — they go directly between the two browsers over WebRTC.
Is a VPN a way to make LAN tools work across networks?
Sometimes, and it is more work than it sounds. A mesh VPN such as Tailscale or ZeroTier puts both devices on one virtual network, which can restore local discovery — but some tools rely on broadcast traffic that mesh VPNs do not forward by default, so it depends on the tool. It also means installing and configuring software on both devices, which is the thing most people were trying to avoid.