ZapFast brings a native Rust and egui WhatsApp client to Linux, macOS and Windows

An unofficial WhatsApp desktop client written in Rust and built with the egui toolkit has surfaced on the front page of Hacker News. According to the project's GitHub repository, ZapFast runs natively on Linux, macOS and Windows with no bundled browser engine, links to a phone as a companion device, and — in the developers' own Linux testing — opens in under a second while idling at roughly 200 MB of RAM. For comparison, they measured WhatsApp Web at 1.13 GB.

What the client covers

The repository describes a feature set that goes beyond basic messaging: formatted text, replies, edits, reactions, forwards, images, files, stickers, GIFs, polls and voice messages, with voice notes, videos, round video messages, GIFs and animated stickers all playable inside the chat view.

Chats are kept in an encrypted archive on the local machine, and older history can be fetched from the phone as you scroll upward. That archive can be exported as plain text or as a ZIP file containing downloaded attachments. Several WhatsApp numbers can be linked at once and switched between inside a single window.

On the desktop side, the app offers keyboard shortcuts, text selection and copying across multiple messages, and tray residency with native notifications on all three platforms — clicking a notification opens the announced message, and reading a chat withdraws its outstanding alerts. Themes come in light, dark, system-following and custom variants, with an option to follow the desktop theme on Omarchy systems. Privacy features include hiding locked chats behind a code and locking the entire window behind an app lock, and the developers state that no data is sent to any server of theirs. The interface is available in numerous languages, including English, French, German, Spanish, Russian, Turkish and both Simplified and Traditional Chinese.

How it connects

Rather than holding an account of its own, ZapFast uses the same companion-device flow as WhatsApp's official desktop and web apps: it displays a QR code to scan from WhatsApp's linked-devices settings, or an eight-character code to enter alongside your phone number. The underlying protocol work comes from the whatsapp-rust library.

The link survives restarts, and the phone does not need to remain online to read messages ZapFast has already stored locally, according to the repository's documentation.

Performance claims and the stack

The headline numbers — sub-second launch and around 200 MB of idle memory versus 1.13 GB for WhatsApp Web — are the developers' own measurements from a Linux test, not an independent benchmark. Still, they illustrate the project's premise: instead of wrapping the web client in a browser engine, ZapFast renders its interface with egui and fastframe, a framework the same team uses for a family of native desktop apps, including a sibling Spotify client called Spotifast.

Getting it

ZapFast is distributed as a Homebrew cask on macOS, a zapfast-bin package on Arch Linux, and a choice of Windows builds, with Nix and AppImage options listed for other Linux distributions; it can also be built from source. The project is MIT-licensed, and contributors can launch a demo mode that lets them inspect the interface without a WhatsApp account.

The caveat

The repository is explicit that ZapFast is unofficial and unaffiliated with WhatsApp or Meta. It warns that using an unofficial client may breach WhatsApp's terms of service and could lead to account suspension, and tells users to proceed at their own risk.

Why it matters

Desktop messaging has largely converged on Electron-style wrappers around web clients, which is convenient to ship but carries a heavy memory and startup cost. ZapFast is a working demonstration that a companion-device protocol, once implemented in Rust, can back a genuinely native GUI at a fraction of that footprint — an attractive proposition for older hardware and for Linux, where first-party support has often lagged. The trade-off is structural: the app depends on a third-party protocol library and on Meta's tolerance of unofficial clients, so the ban risk the developers themselves flag is real. Whether or not this particular app thrives, it adds a concrete data point to the broader push for fast, native alternatives to browser-based desktop software.