ToggleMouse

Share one Mac's mouse and keyboard with other Macs on the same network. It's a free, open alternative to Universal Control that doesn't need a shared Apple ID. You switch with a keyboard shortcut or by pushing the cursor through a screen edge. The same app runs in two modes:

• Emitter: the Mac the mouse and keyboard are plugged into. A per-receiver shortcut toggles streaming to that receiver.
• Receiver: replays the streamed input as if it were local.

The menu bar icon is grey when idle, red while emitting and green while receiving.

Status: early and experimental. There are no prebuilt downloads; build it from source. The encryption hasn't been audited; see SECURITY.md.

Requirements

• macOS 14 or later, on Intel or Apple Silicon (builds are universal).
• Xcode 16 or later to build.
• Both Macs on the same local network. Wi-Fi works; Ethernet is smoother.

Build

git clone https://github.com/slash4/ToggleMouse.git
cd ToggleMouse
swift test                      # protocol, crypto and smoothing tests
./scripts/build-app.sh          # builds build/ToggleMouse.app and build/ToggleMouse.zip

Signing

The build script signs with $SIGN_IDENTITY if set. Otherwise it uses the first Developer ID Application identity in your keychain, then the first Apple Development identity, and falls back to ad-hoc signing.

SIGN_IDENTITY="Apple Development: Your Name (TEAMID)" ./scripts/build-app.sh

A free Apple Account in Xcode is enough to get an Apple Development certificate. Signing with a real certificate matters for two reasons:

• macOS ties the Accessibility permission and the Keychain item to the signature, so an ad-hoc build asks for permission again after every rebuild.
• The AirDrop helper checks that the app and helper share a team ID, so it doesn't work in ad-hoc builds. Everything else does.

Installing on another Mac

Copy build/ToggleMouse.zip to the other Mac, rather than the bare .app: some network shares add metadata that breaks the signature. Unzip it into /Applications. A build signed with a development certificate isn't notarized, so the first time macOS blocks it. Open it once, then click Open Anyway in System Settings › Privacy & Security.

Both Macs must run builds of the same commit. The protocol isn't versioned yet, and mismatched builds fail to connect.

Permissions

• Accessibility: the emitter needs it to capture the mouse and keyboard, and the receiver needs it to replay them.
• Local Network: to find and connect to the other Mac.
• Login Items (optional): approves the AirDrop helper. See below.

Setup

1. Install ToggleMouse.app on both Macs and open it.
2. Grant Accessibility (System Settings › Privacy & Security) on both Macs, and allow Local Network access when asked.
3. On the receiver, choose Receiver and click Allow Pairing for 2 Minutes.
4. On the emitter, choose Emitter and click Pair… next to the receiver, or enter its IP.
5. Both Macs show a 6-digit code. If the codes match, click Codes Match on each Mac.
6. Press the receiver's shortcut (default ⌃⌥⌘1, ⌃⌥⌘2, …) to stream to it. Press it again to take control back. Click the shortcut button in the window to change it.
7. Optional: under each receiver, set Screen edge to the side of the emitter it sits on. Push the cursor through that edge to switch to it, and through the opposite edge on the receiver to come back. The cursor crosses at the matching height. Edges where another display continues, and drags, never switch.

How it works

• Discovery: receivers advertise _togglemouse._tcp over Bonjour on TCP port 52525. Each paired receiver can also use a fixed address, which overrides Bonjour.
• Pairing: each Mac has a Curve25519 key pair in its login Keychain. Pairing works like Bluetooth numeric comparison. The emitter commits to its key before it sees the receiver's key, then both Macs show a code derived from both keys and both nonces. A man in the middle gets the same code on both sides only 1 time in 10⁶, and each attempt needs a user to confirm it. The paired public keys are stored in ~/Library/Application Support/ToggleMouse/peers.json.
• Sessions: a Noise-KK-style handshake combines the two pinned static keys with fresh ephemeral keys. Traffic uses ChaCha20-Poly1305 with a separate key for each direction and counter nonces, so replayed or altered frames are rejected. A Mac without the paired private key can't complete the handshake.
• Transport: keys, clicks, scroll and heartbeats use TCP (Nagle off), so nothing is lost or reordered. Pointer movement uses UDP on the same port, encrypted with a separate session key. Each datagram carries the running total of movement plus a sequence number, so a lost datagram costs nothing and stale ones are dropped. The latest total is also sent over TCP before each click or scroll, and every 100 ms in case UDP is blocked. Datagrams are marked as interactive voice traffic for Wi-Fi priority, and the app opts out of App Nap so macOS doesn't throttle it in the background.
• Smoothing: Wi-Fi delivers packets in bursts. The receiver uses a jitter buffer instead of applying each update on arrival. Each update carries its capture time on the emitter. The receiver schedules it at that time, plus the lowest delay seen recently, plus a buffer that adapts between 2 and 40 ms. The buffer covers 95% of the measured variation and one mouse report interval. A 2 ms timer on a dedicated high-priority thread moves the cursor along the interpolated path. Clicks and scrolls flush the buffer first, so they land where the cursor is.
• AirDrop helper: AWDL (the Wi-Fi peer-to-peer link behind AirDrop, Universal Control, Sidecar and AirPlay) hops the radio between channels, which delays packets in bursts. With "Turn off AirDrop while streaming" checked, a privileged helper (ToggleMouseHelper, registered through SMAppService and approved in System Settings › General › Login Items) keeps awdl0 down while a stream is active on that Mac. AWDL comes back when streaming stops, or when the app quits or crashes, if it was up before. The helper only accepts XPC connections from ToggleMouse signed by the same team, can only switch awdl0, and exits when idle. Unchecking the setting unregisters it.
• Capture: an active CGEventTap on the emitter swallows input while streaming and freezes the local cursor with CGAssociateMouseAndMouseCursorPosition. Keys are sent as raw key codes. Media keys (volume, mute, playback, brightness, keyboard backlight, eject) are captured as system-defined events and replayed as the same events; Power, Caps Lock and Help stay local.
• Failsafe: the emitter sends a heartbeat every 2 s. If the link drops or goes silent for 6 s, the emitter takes control back. When a stream ends or drops, the receiver releases every key, button and modifier that is still held.

Limitations

• Movement, buttons, scroll, keys and media keys only. No gestures, clipboard or login window.
• While Secure Input is on (for example, a focused password field on the emitter), macOS hides keystrokes from the event tap.
• The emitter's cursor stays visible, frozen in place, while streaming.
• No protocol version check: mismatched builds don't connect, and don't say why.
• No launch at login yet.

Contributing

Issues and pull requests are welcome. Run swift test before sending a change. When reporting a bug, include both Macs' models and macOS versions, and the network type.

License

MIT