# How StrongFolder works

Source: https://help.strongfolder.com/en/how-it-works/
Updated: 2026-11-05

> StrongFolder turns your browser into the server for your own files. You choose files or a folder and get a link; when the recipient opens it, StrongFolder connects the two browsers over an encrypted WebRTC connection and streams the files straight from your device to theirs. Nothing is uploaded or stored, so your tab must stay open.

1. **Pick files or a folder** — Open [strongfolder.com](https://strongfolder.com) or the Chrome extension and choose files with **Upload Files** or a whole folder with **Upload Folder**. Nothing leaves your device yet.
2. **Share the link** — Copy the link, use Share, or show the QR code. Send it any way you like: chat, e-mail, SMS.
3. **The recipient opens the link** — They see the file names and sizes and click Download. No account, no app.
4. **Direct transfer** — The two browsers connect and the files stream from your device to theirs. Keep your tab open until the counter shows the download is complete.
5. **Stop sharing** — Click **Stop Sharing** or close the tab. The link stops working, and nothing remains on a server.

## What happens when I share a file?

A classic transfer service works in two halves: you **upload** the whole file to a server,
then the recipient **downloads** it from there. StrongFolder removes the server in the middle.
When you pick files, your browser only reads their names and sizes and creates a session; the
data stays on your disk. The link you send points to that session.

When the recipient opens the link, a small signalling service introduces the two browsers to
each other. They exchange network details and open a direct **WebRTC data channel** — the same
kind of connection browsers use for video calls. From then on the files flow from your device
to theirs, piece by piece, while both tabs are open.

**Key facts**

- Transport: WebRTC data channels (peer-to-peer) between the sender's and the recipient's browsers.
- Encryption: WebRTC encrypts every data channel with DTLS, so the file stream is encrypted in transit on every connection.
- Storage: Files are never uploaded to or stored on a StrongFolder server.
- Fallback: 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.
- Requirement: 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.

## Why is there no upload bar?

Because nothing is uploaded. With a cloud service you first wait for 100% upload, and only
then can anyone download. With StrongFolder the recipient starts receiving the first bytes as
soon as the connection is up. For big files this often halves the total time: there is one
transfer instead of two.

## How fast is a direct transfer?

A direct transfer runs at the speed of the **slower** side: usually the sender's upload speed.
At 50 Mbit/s upload, 10 GB takes roughly 27 minutes; at 500 Mbit/s, under 3 minutes. Both
devices on the same office or home network can be much faster. A relayed connection is
usually slower than a direct one.

| Your upload speed | 1 GB | 10 GB | 100 GB |
|---|---|---|---|
| 10 Mbit/s | ~13 min | ~2.2 h | ~22 h |
| 50 Mbit/s | ~3 min | ~27 min | ~4.4 h |
| 100 Mbit/s | ~1.3 min | ~13 min | ~2.2 h |
| 500 Mbit/s | ~16 s | ~3 min | ~27 min |

*Theoretical times at a steady speed (1 GB = 1,000 MB); real transfers are a little slower.*

## How are folders sent?

When you choose a folder, StrongFolder shares the whole tree: every subfolder and file name.
On the recipient's side, Chrome, Edge, Opera and other Chromium browsers on a computer can
write the same tree straight to disk, file by file, without zipping. Other browsers download
the files one by one or as a ZIP. See [How to send a folder without
zipping](https://help.strongfolder.com/en/guides/send-folder-without-zipping/).

## What do I need?

- **Sender:** A modern browser with WebRTC; Google Chrome or another Chromium browser on a computer works best. The Chrome extension adds a one-click button to Chrome.
- **Recipient:** any modern browser; Chrome, Edge or Opera on a computer to save whole folders.
- **Both:** an internet connection at the same time. The sender's tab stays open until the end.

Full list: [Limits & requirements](https://help.strongfolder.com/en/limits/).

[Send files now](https://strongfolder.com)
## Web app or Chrome extension?

Both do the same transfer. The [web app](https://strongfolder.com) works in any browser, on any
computer. The [Chrome extension](https://help.strongfolder.com/en/chrome-extension/) puts StrongFolder next to the address bar,
so you can share a file or folder from any page in one click.

## FAQ

### Do the files go through your server?

Normally no: the two browsers connect directly. If a direct path is blocked by a firewall or network, the encrypted stream is passed through a StrongFolder relay (TURN) server, which forwards it without storing it.

### What does StrongFolder keep?

To create the link, the service keeps transfer metadata: file and folder names, sizes and the number of files. Files are never uploaded to or stored on a StrongFolder server.

### Can several people download from one link?

One link can be opened by several recipients; each downloads directly from the sender. Each extra recipient uses your upload bandwidth, so downloads share your connection.

### What happens if I close the tab?

The link works while the sender keeps sharing. When the sender clicks Stop Sharing or closes the tab, the files are no longer available. A download in progress stops; the recipient can start again when you share the files again.

### Do I need the Chrome extension?

No. The web app at strongfolder.com does the same in any modern browser. The extension only puts StrongFolder one click away in Chrome's toolbar.