PairOnce

TESTED · LARGE FILES · RESUME

Large files and resume in the browser: what we tested, and when

We ran PairOnce on real browsers and phones and wrote down what happened, with the date and the version. Chrome and Edge on Windows wrote a 3 GiB file to disk with every checked byte correct. A 1.5 GiB file cut at 40% continued from where it stopped and arrived identical to the original (matching SHA-256). Resume also worked in Firefox 158 and on an iPhone with Safari on iOS 26.3.

A file of up to 2 GB goes to a receiving Chrome or Edge (computer or Android phone), Firefox (computer) or Safari on iOS 26 or later. A file over 16 MB that is cut off continues once the same two devices reconnect within 30 minutes, with both pages still open.

Every number below comes from a test we ran on the date shown. Anything we have not tested is left out.

Step by step

  1. Check the receiving browser. Chrome or Edge on a computer or an Android phone, Firefox on a computer, or Safari on iOS 26 or later takes a file of up to 2 GB. Other receivers take up to 50 MB per file.
  2. Open PairOnce on both devices and 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. Choose the file and accept it. Tap Choose files on the sender. The receiver accepts the file and saves it when it arrives.
  4. If the connection drops, keep both pages open. A file over 16 MB continues from where it stopped when the two devices reconnect within 30 minutes. Nothing needs to be sent again from the start.

Writing a 3 GiB file to disk (23 October 2026)

Method: Windows 11, real browser profiles, a 3 GiB file written in 8 MiB pieces to the browser’s private storage the way PairOnce receives a large file, then saved to the Downloads folder. We checked 16 bytes across the file, including the positions around the 2 GiB mark.

Chrome 155: written in 62.8 seconds (49 MiB/s), saved to Downloads in 141.8 seconds, size 3,221,225,472 bytes, every checked byte correct. Edge 155: written in 66.7 seconds (46 MiB/s), saved in 130.7 seconds, same size, every checked byte correct.

The page used 9 to 10 MiB of memory at its peak, because the file goes to disk piece by piece and is never held in memory. What limits the size is the browser’s storage quota for the site (10 GiB in these runs, and it varies with free disk space), and saving to Downloads needs the same amount of space again. In a temporary profile, which works like a private (incognito) window, both browsers ran out of storage for this file, so use a normal window for a very large file.

A cut-off 1.5 GiB file continues (2 November 2026)

Method: two Chrome windows on one computer, with the release build running on a local server. We sent a 1.5 GiB file and closed the connection at 644 MB. After the two pages reconnected, the transfer continued from 656 MB instead of from zero, the remaining part took 81 seconds, and the SHA-256 of the received file matched the original.

Resume in other browsers

Firefox 158 on Windows (3 November 2026, receiving from Chrome through the live service): cut at 25 MB, continued at 26 MB, SHA-256 matched.

Safari on iOS 26.3, an iPhone 17 (3 November 2026): a 42 MB file cut at 17 MB continued at 17 MB and arrived complete, relayed.

Safari on iOS 18.6 (3 November 2026): the browser cannot write a large file to disk, so it takes files up to 50 MB, and a file cut off is sent again from the start once the phone reconnects. Use iOS 26 or later on the receiving iPhone for large files.

A real network drop on real phones (3 November 2026): Wi-Fi switched off and on in the middle of a transfer, and the transfer resumed.

Phones and the receive path (6 November 2026)

On real devices in the AWS Device Farm, a Galaxy S24 Ultra (Android 14, Chrome), an iPhone 17 Pro (iOS 26.3, Safari) and an iPhone 11 (iOS 18.6, Safari) each opened an invitation link, showed the confirmation card, connected after the host approved, and sent a 5 MiB file that the computer received. On the Galaxy, a file saved on the phone had the same hash as the original.

Two phones paired with each other (iPhone 11 typed the code of the Galaxy, the Galaxy approved) and a 3 MiB file arrived, relayed. With every UDP relay address blocked, two Chrome windows still connected in about 10 seconds and received the file through the other relay routes.

How these tests are done

The tests run against the live service or the same code that runs it, with real browsers and real devices, and the results are kept with the date and the version. The protocol and its security model are public in the PairOnce protocol and threat model.

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

  • A cloud drive or a link service. Fits when the receiver is offline: the file waits on a server until they download it. See direct transfer or cloud drive.
  • A USB drive. No network needed; format it as exFAT so Mac and Windows can both read and write it.
  • LocalSend. A free open-source app that sends over the local network without the internet. See the LocalSend comparison.

Common questions

How big a file can the browser receive?

Up to 2 GB per file on a receiving Chrome or Edge (computer or Android), Firefox (computer) or Safari on iOS 26 or later. The disk-write test above wrote 3 GiB in Chrome and Edge.

What happens if the connection drops in the middle of a large file?

A file over 16 MB continues where it stopped when the same two devices reconnect within 30 minutes, with both pages open. In our 2 November 2026 test a 1.5 GiB file continued from 656 MB and arrived identical to the original.

Does resume work on an iPhone?

Yes with Safari on iOS 26 or later (tested on iOS 26.3 on 3 November 2026). On iOS 18.6 the browser cannot write large files to disk, so it takes files up to 50 MB and a cut-off file starts again.

Why did a very large file fail in a private window?

A private (incognito) window has far less storage for the site. In our test both Chrome and Edge ran out of it with a temporary profile, which works the same way. Open PairOnce in a normal window to receive a very large file.