GitHub - denislupookov/altersend: Send files directly between devices over the internet - no cloud, no servers, no size limits.

File transfer without the cloud storage.

Files go directly between your devices — end-to-end encrypted, no accounts, no servers, no limits.

About

AlterSend is a free, open-source app for sending files directly between your devices — no cloud, no uploads, no size limits. Files transfer peer-to-peer and are end-to-end encrypted; nothing is ever stored on a server.

Why use WeTransfer, Dropbox, or Google Drive when you can send files directly — instantly, privately, with no upload costs and no limits?

Features

No accounts — no signup, no login, no email address required
No servers — files transfer directly device-to-device, nothing stored in the cloud
End-to-end encrypted — only your devices can read your files, always
No file size limit — send a 100 MB photo or 500 GB video archive, same experience
Pair your devices — pair a device once, then send to it without scanning or typing a code each time
Cross-platform — macOS, Windows, Linux, iOS, Android
Works everywhere — local network or across continents, same code path
Multi-language — fully translated UI, available in 12 languages
Open source — Apache-2.0, audit every line yourself

Download

Get the latest release from altersend.com/download or directly from the table below.

Platform	Download
Windows	Microsoft Store (signed) · EXE installer
macOS	DMG — Apple Silicon · DMG — Intel · Homebrew
Linux	AppImage
Android	Google Play · APK
iOS	App Store

Windows .exe — not yet signed, so Windows will show "Windows protected your PC" on first run. Click More info → Run anyway to install. The Microsoft Store version is signed and avoids this warning.

macOS Homebrew

You can also install AlterSend on macOS using Homebrew:

brew install --cask altersend

How it works

Open AlterSend on both devices
One device shows a join code (or QR)
The other scans or types it
Files transfer directly — peer to peer

   ┌─────────┐          encrypted P2P          ┌─────────┐
   │ Device  │ ◄──────────────────────────────► │ Device  │
   │   A     │     direct, no middleman         │   B     │
   └─────────┘                                  └─────────┘
        ▲                                            ▲
        │       peer discovery via Hyperswarm        │
        └────────────────────────────────────────────┘
                   (DHT, no central server)

Under the hood

AlterSend is built on Hyperswarm, a Kademlia DHT at its core. Behind those four steps:

A random 32-byte key is generated for each transfer (crypto.randomBytes(32)). That 64-char hex string is the join code you share.
Peers rendezvous on a hash of that key, not the key itself. Both sides compute the same discovery key — a BLAKE2b hash derived from the join code — and join the DHT on that. The raw key never leaves your device, only its hash is published.
Public bootstrap nodes are the only entry point. A handful of them get peers onto the DHT. After that, no central server is involved — and there's no relay fallback, so if direct hole-punching fails, the connection fails.
The connection is direct and end-to-end encrypted. Peers connect over a Noise-encrypted socket, and the sender shares its Hyperdrive key over that channel. Files are imported into the sender's local Hyperdrive, replicated to the receiver's, then written out to disk — so in v1 each side needs roughly 2× the transfer size in free space while a transfer runs. (Working to improve this.)

Pair once, skip the code. You can pair devices you own so future transfers go straight through — no code to scan or type. Pairing only stores a public device key, the secret stays in your OS keychain, and a paired device is recognized without exposing your identity to anyone else. See docs/architecture.md for the full design.

For developers

Prerequisites

Node.js 20+
npm 10+
Xcode (iOS) or Android Studio (Android)

Setup

git clone https://github.com/denislupookov/altersend.git
cd altersend
npm install

cp apps/desktop/.env.example apps/desktop/.env
cp apps/mobile/.env.example apps/mobile/.env
# All env vars are optional in dev — the app runs without them.

Run

npm run dev            # desktop (Electron)
npm run mobile:start   # mobile (Expo)

Build

npm run desktop:build  # packages + desktop app

Platform installers (.dmg, .exe, .AppImage) are produced by the release CI workflow — trigger manually from the Actions tab.

Project structure

apps/
  desktop/    Electron app — main + renderer + Bare worklet
  mobile/     React Native / Expo app
packages/
  core/       P2P protocol — Hyperswarm, Hyperdrive, RPC
  domain/     State management — Zustand store, business logic
  components/ Cross-platform UI — React Strict DOM + Tailwind
  locales/   Shared locale metadata, i18next setup, and catalogs
docs/
  architecture.md   Full system overview
  i18n.md           Translation workflow and locale coverage

See docs/architecture.md for data flow and inter-process boundaries.

Internationalization

Desktop and mobile share translation catalogs through @altersend/locales, currently covering 12 locales. See docs/i18n.md for the translation workflow.

Tech stack

Electron · React Native · Expo · Bare · Hyperswarm · Hyperdrive · React Strict DOM · Tailwind · Zustand

Crash reporting

Crash reporting via Sentry is opt-in and off by default.

Contributors

Contributing

Pull requests welcome. See CONTRIBUTING.md for setup, code style, and the PR process.

Security

Found a vulnerability? Follow the disclosure process in SECURITY.md — please don't open a public issue.