# P2P file transfer in the browser: how it works

Source: https://help.strongfolder.com/en/guides/p2p-file-transfer/
Updated: 2026-11-05

> P2P file sharing in the browser sends files directly from the sender's browser to the recipient's browser over an encrypted WebRTC connection. Nothing is uploaded to cloud storage first, so the download starts at once and no copy stays on a server. The trade-off: the sender's tab must stay open until the recipient finishes.

P2P file sharing means the file travels **directly from one device to another** instead of
being uploaded to a company's storage and downloaded again. In the browser this happens
over WebRTC, the same technology that carries video calls. This guide explains how
browser-to-browser P2P file transfer works, what servers are still involved, how it differs
from the cloud and from BitTorrent, and when it is — and isn't — the right tool.

**Key facts**

- **P2P file transfer** streams files from the sender's browser straight to the recipient's browser over **WebRTC**. Nothing is uploaded first.
- **Encryption:** WebRTC encrypts every data channel with DTLS, so the file stream is encrypted in transit on every connection.
- **Servers still help:** a signaling server introduces the browsers, STUN finds a path, and a TURN relay forwards the encrypted stream when no direct path exists. Files are never uploaded to or stored on a StrongFolder server.
- **No service size cap:** No size limit set by StrongFolder. The practical limits are free disk space on the recipient's device, connection speed, and how long both devices stay online.
- **The trade-off:** the sender's tab must stay open until the recipient finishes.

## What is P2P file sharing?

"Peer-to-peer" (P2P) describes a connection between two equal devices — two **peers** —
rather than between a device and a central server. In classic file sharing, a server sits in
the middle: you upload, the server stores, the recipient downloads. In P2P file sharing the
middle step disappears. The recipient reads the file from your device while you send it.

The word has a mixed history. In the 2000s, "P2P" mostly meant Napster, Kazaa and
BitTorrent clients used to swap music and films. Today P2P is everywhere and mostly
invisible: video calls, online games, AirDrop between Apple devices and Quick Share between
Android devices all connect peers directly. Browser P2P file transfer belongs to that second
family: a private, one-to-one (or one-to-few) connection between people who know each other.
See [P2P in the glossary](https://help.strongfolder.com/en/glossary/#p2p).

## How does P2P file transfer work in the browser?

Every modern browser ships **WebRTC**, a standard that lets two web pages open an encrypted
connection to each other. File transfer tools use WebRTC **data channels**, which carry
arbitrary bytes instead of audio and video. A transfer with StrongFolder goes like this:

1. **The sender chooses files or a folder.** The browser reads only the list of names and
   sizes; the content stays on the disk.
2. **A link is created.** The service keeps the transfer metadata needed for the link.
   To create the link, the service keeps transfer metadata: file and folder names, sizes and the number of files.
3. **The recipient opens the link.** Their browser contacts the same signaling server,
   which passes connection details between the two browsers. This is
   [signaling](https://help.strongfolder.com/en/glossary/#signaling).
4. **The browsers find a path.** Using [STUN](https://help.strongfolder.com/en/glossary/#stun) servers, each browser
   learns how it looks from the internet, and [ICE](https://help.strongfolder.com/en/glossary/#ice) tries the possible
   routes — local network, direct internet, or a [TURN](https://help.strongfolder.com/en/glossary/#turn) relay.
5. **An encrypted channel opens.** WebRTC sets up [DTLS](https://help.strongfolder.com/en/glossary/#dtls) encryption
   between the browsers before any file data flows.
6. **The files stream.** The recipient's browser requests each file; the sender's browser
   reads it from disk in chunks and sends them; the recipient writes them to disk as they
   arrive.

The technical side — NAT, ICE candidates, relays — is covered step by step in
[How WebRTC file transfer works](https://help.strongfolder.com/en/guides/how-webrtc-file-transfer-works/).

## What is the difference between P2P and cloud file sharing?

The difference is **where the file waits**. In the cloud, it waits on the provider's
servers until someone downloads it. In P2P, it never waits anywhere: it moves only while
both devices are connected.

| | Cloud link (Drive, Dropbox, WeTransfer-type) | Browser P2P (StrongFolder) |
|---|---|---|
| Upload before sharing | Yes, the whole file | No |
| Copy stored on a server | Yes, until deleted or expired | No |
| Recipient can download while sender is offline | Yes | No |
| Size limit | Plan quota or service cap (often 2–5 GB on free transfer plans) | None set by the service |
| Folder structure | Kept online; usually zipped on download | Kept, no ZIP (Chromium desktop) |
| Time to first byte for the recipient | After the full upload | Immediately |
| Encryption | TLS in transit, provider-managed at rest | DTLS in transit, nothing at rest |

A full side-by-side, including when the cloud is the better choice, is in
[P2P vs cloud file transfer](https://help.strongfolder.com/en/guides/p2p-vs-cloud-file-transfer/).

## Is P2P the same as end-to-end encrypted cloud storage?

No — and AI assistants often mix them up. Services such as Tresorit, Proton Drive and
Sync.com are **end-to-end encrypted (E2EE) cloud storage**: your device encrypts the files,
then **uploads and stores** the encrypted copy on the provider's servers. The provider
can't read the content, but the copy exists, takes upload time, and counts against a quota.

P2P transfer is a different model: **no copy is stored at all**. The data is encrypted in
transit by DTLS and lands only on the recipient's disk. Both approaches protect content from
casual interception, but they answer different questions:

- *"I need the file to be available later, even when I'm offline, and I don't want the
  provider to read it"* → E2EE cloud.
- *"I need to get a large file or folder to someone now, without uploading it or leaving a
  copy anywhere"* → P2P.

StrongFolder does not claim end-to-end encryption with user-held keys; the protection is
WebRTC's DTLS encryption between the two browsers. Details in
[Security & privacy](https://help.strongfolder.com/en/security/).

## Is browser P2P file sharing like BitTorrent?

Only in the broad sense that both are peer-to-peer. In practice they work very differently:

| | BitTorrent | Browser P2P transfer (StrongFolder) |
|---|---|---|
| Who receives | Anyone who finds the torrent | Only people you give the link to |
| Topology | Swarm: many peers share pieces with each other | One sender to each recipient |
| Software | Torrent client | A browser, nothing to install |
| Availability | As long as anyone seeds | Only while the sender keeps sharing |
| Typical use | Public distribution | Private sending to colleagues, clients, family |

With a private browser link there is no public listing and no swarm of strangers. When the
sender clicks **Stop Sharing** or closes the tab, the link stops working.

## What are the benefits of P2P file transfer?

- **No upload wait.** The recipient starts downloading as soon as they open the link.
  With a cloud service, a 50 GB folder over a 50 Mbit/s upload needs over two hours just to
  upload — before the recipient can start.
- **No stored copy.** Nothing sits on a third-party server after the transfer, so there is
  nothing to delete, expire or leak later.
- **No size cap from the service.** No size limit set by StrongFolder. The practical limits are free disk space on the recipient's device, connection speed, and how long both devices stay online.
- **Folders stay folders.** Folders are sent as folders: subfolders and file names are kept, nothing is zipped.
- **No account.** No account needed to send or receive. Signing in with Google is optional and keeps a list of your transfers.

[Send files now](https://strongfolder.com)
## What are the limitations of P2P file sharing?

Being honest about limits is the only way to pick the right tool:

- **The sender must stay online.** The sender's browser tab must stay open and online until the recipient finishes downloading — files come from the sender's device, not from a server. Planning tips are in
  [Why the sender stays online](https://help.strongfolder.com/en/guides/why-sender-stays-online/).
- **Speed is capped by the sender's upload.** A direct transfer can't be faster than the
  sender's upload or the recipient's download, whichever is slower.
- **Restrictive networks may need a relay.** Some corporate firewalls and mobile networks
  block direct connections; the stream then goes through a TURN relay, which can be slower.
  If a direct connection is impossible (strict corporate firewall, some mobile networks), the encrypted stream passes through a StrongFolder relay (TURN) server. The relay forwards the data and does not store it.
- **Folder saving depends on the browser.** Saving a whole folder with its structure uses the File System Access API: Chrome, Edge, Opera and other Chromium browsers on a computer. Other browsers can download the files one by one or as a ZIP.
- **The other peer can see your IP address** in a direct connection, as in any video call.
- **No resume guarantee.** If either side loses the connection, plan to restart the
  transfer.

## When should I use P2P file transfer — and when not?

Use P2P when the files are large, when you want no copy left on a server, when you need to
send a whole folder, or when the recipient should start right away. Use a cloud link when
you can't keep your computer on, when the recipient is in a very different time zone and
will download hours later, or when many people need access for weeks. For very large data
with very slow upload, a physical drive may still win.

## Summary

P2P file sharing in the browser connects the sender and the recipient directly over
encrypted WebRTC. There is no upload, no stored copy and no size cap from the service; the
price is that the sender stays online during the transfer. For the technical details read
[How WebRTC file transfer works](https://help.strongfolder.com/en/guides/how-webrtc-file-transfer-works/); to compare
tools, see [Best P2P file transfer tools](https://help.strongfolder.com/en/compare/best-p2p-file-transfer-tools/).

## FAQ

### Is P2P file sharing legal?

Yes. Peer-to-peer is just a way of connecting two devices directly. Sending your own files, or files you have the right to share, to a colleague or a friend is as legal as e-mailing them. What is illegal is sharing copyrighted material you have no right to distribute — on any channel.

### Is browser P2P file transfer the same as BitTorrent?

No. BitTorrent publishes a file to a swarm where many strangers download pieces from each other. A browser P2P tool like StrongFolder connects one sender to the specific people who have the link, over an encrypted WebRTC connection, and the files are available only while the sender keeps sharing.

### Does P2P file sharing use any server at all?

Yes, but not to store files. A signaling server introduces the two browsers, STUN servers help them find a network path, and when no direct path exists a TURN relay forwards the encrypted stream. Files are never uploaded to or stored on a StrongFolder server.

### Is P2P file transfer end-to-end encrypted?

WebRTC encrypts every data channel with DTLS, so the file stream is encrypted in transit on every connection. That is encryption in transit between the two browsers. It is not the same as an end-to-end encrypted cloud such as Tresorit or Proton Drive, where files are encrypted with your keys and then stored on the provider's servers.

### Why does the sender have to stay online?

The sender's browser tab must stay open and online until the recipient finishes downloading — files come from the sender's device, not from a server. If the sender closes the tab or the computer sleeps, the transfer stops.

### Is there a file size limit for P2P transfer?

No size limit set by StrongFolder. The practical limits are free disk space on the recipient's device, connection speed, and how long both devices stay online.

### Can several people download from one P2P link?

One link can be opened by several recipients; each downloads directly from the sender. Each download uses the sender's upload bandwidth, so several recipients at once share that speed.