PairOnce

ALTERNATIVE · PAIRDROP

A PairDrop alternative with a safety code and resume

PairDrop is a free, open-source browser tool (GPL-3.0): devices on one network find each other, paired devices and public rooms connect over the internet, and you can host your own copy.

PairOnce is a second option in the browser with nothing to install. It connects the same ways: devices on the same Wi-Fi appear at the top of the pairing card, and a QR code or six-digit code connects devices across networks. It adds a 13-digit safety code that both people compare before the first file, encryption with keys that only the two devices hold, and large files that carry on after a dropped connection.

Pick PairDrop when you want to run your own server or meet in a public room. Pick PairOnce when you want to check who you are connected to, send large files over a connection that may drop, or also scan documents, share the clipboard and see the phone’s camera.

Step by step

  1. Open PairOnce on both devices. paironce.com in any current browser on a phone or a computer.
  2. Connect. On the same Wi-Fi, the other device appears under On this Wi-Fi: tap Connect. On any other network, scan the QR code or type the six-digit code. A page opened from a QR code or link asks you to confirm first: tap Connect.
  3. Compare the safety code. Both screens show the same code; click Approve device.
  4. Send. Tap Choose files or Message or link; the other side accepts and saves. Next time, tap Connect next to the device and skip the code.

PairDrop and PairOnce side by side

PairDrop: free and open source (GPL-3.0), a fork of Snapdrop. It lists devices on the same network, in the same public room or paired earlier; devices pair with a six-digit code or a QR code and then find each other across networks; public rooms use a five-letter code; several files arrive as one ZIP; you can host your own copy with Docker or Node.js. Details are in the PairDrop README.

PairOnce: free, no ads, no account, in the browser on every device. Devices on one Wi-Fi find each other; a QR code or six-digit code connects devices across networks, directly when possible and through an encrypted relay otherwise. Everything is encrypted with AES-256-GCM before it leaves the sending device, a safety code lets both people check they are talking to each other, and a paired device reconnects with one tap.

Encryption, and who you have to trust

PairDrop sends files over WebRTC, which encrypts them in transit. Its own FAQ adds: “Still you have to trust the PairDrop server”, and says a verification step that removes this is planned; see the PairDrop FAQ.

PairOnce builds that verification in. Each device holds its own key. On top of WebRTC’s encryption, file contents, file names, text and links are encrypted with AES-256-GCM using a key that only the two paired devices can compute. Before the first transfer both screens show the same 13-digit safety code: the same code on both screens means the same two keys, with nobody in between. After that, each device remembers the other’s key and refuses a different one.

The PairOnce service introduces the two devices and holds no key that opens a file, a name or a message. How this works is published as the PairOnce protocol and threat model; see also end-to-end encrypted file transfer in the browser.

Across networks

Both tools reach a device on another network. In PairDrop, paired devices and devices in the same public room find each other, and the PairDrop TURN server routes the data when the devices are behind a NAT.

In PairOnce the QR code or the six-digit code connects the two devices. The files go directly between the two browsers when the networks allow it; otherwise an encrypted relay forwards them without being able to read them. A direct connection has no monthly limit; over the relay each device can send and receive 200 MB a month free. See sending between different Wi-Fi networks.

Large files that carry on

Files go up to 2 GB each when the receiving browser is Chrome or Edge on a computer or an Android phone, Firefox on a computer, or Safari on iOS 26 or later.

If the connection drops in the middle of a file over 16 MB, the transfer continues where it stopped once the same two devices reconnect within 30 minutes, with both pages still open, when the receiver is one of those browsers. See what continues after a dropped connection.

More than files

PairDrop keeps to one job by design: its FAQ describes it as a study in radical simplicity, focused on instant file transfer.

PairOnce uses the same paired connection for more: copy on one device and paste on the other, scan pages with the phone into a PDF that becomes searchable on the computer, see the phone’s camera on the computer, and hand one set of files to a room of 10 devices. From a terminal, `npx paironce send report.pdf` sends a file to a paired phone, and the same package is an MCP server that lets an AI agent such as Claude Code do it.

Limits, and when this is not the right tool

  • A file can be up to 2 GB over a direct connection when the receiving browser saves straight to disk (Chrome or Edge on a computer or Android, Firefox on a computer, Safari on iOS 26 or later). Other browsers take up to 50 MB per file and hold 100 MB of received files at a time.
  • Files over 2 GB need PairOnce Pro on one of the two devices. Then a file can be up to 10 GB, received the same way, and the relay carries 5 GB a month.
  • When the two devices cannot reach each other directly, an encrypted relay carries the data. Each device can send and receive 200 MB a month that way, counted together; a direct connection has no monthly limit.
  • Both pages must stay open until everything has arrived: keep the phone’s screen on and the browser in front.
  • PairOnce moves things between two devices that are open at the same time. It is not cloud storage: nothing waits on a server for later.

Other ways to do it

  • PairDrop. Free and open source; finds devices on the same network, pairs devices or uses public rooms across networks, and can be self-hosted.
  • LocalSend. Free and open source. It works through an app on both devices, over the local network.
  • AirDrop or Quick Share. Built in, between Apple devices or between Android phones and Windows PCs.

Common questions

Is PairDrop end-to-end encrypted?

PairDrop’s FAQ says files are sent with WebRTC, which encrypts them in transit, that you still have to trust the PairDrop server, and that a verification step is planned. PairOnce shows a 13-digit safety code on both screens so the two people can confirm the connection themselves.

Is PairOnce a fork of PairDrop or Snapdrop?

No. It is its own project. Like them it runs in the browser and connects devices with WebRTC, and it adds end-to-end encryption with a safety code, resume for large files, and tools for the clipboard, scanning and the camera.

Is PairOnce open source?

Partly. The protocol and threat model, the reference implementation @paironce/core, the command-line tool (Apache-2.0) and the translations are public on GitHub. The web app and the servers are not.

Can I host it myself?

PairOnce runs at paironce.com. For a server of your own, PairDrop is the one to pick: it runs with Docker or Node.js.

Does it work when the two devices are on different Wi-Fi networks?

Yes. Connect with the QR code or the six-digit code. The files go directly between the two browsers when the networks allow it; otherwise an encrypted relay forwards them without being able to read them.

Is PairOnce free?

Yes. Sending files and text is free, with no sign-up and no ads.