A lightweight macOS menu bar app that automatically switches between function keys and media keys based on the active application.
When a configured app (e.g., IntelliJ IDEA) is in the foreground, F1–F12 act as standard function keys. Switch to any other app and they revert to media keys (brightness, volume, etc.).
- Tested on: macOS 26 Tahoe (Apple Silicon M4 Pro)
- Deployment target: macOS 14 Sonoma
- Built with: Swift 6, SwiftUI
The IOKit HIDFKeyMode API used for toggling has been available since at least macOS 10.x and is confirmed working on Tahoe. It should work on Sonoma (14) and Sequoia (15) as well, but these have not been tested. If Apple removes this IOKit interface in a future release, the app will need updating.
Download FNSwitcher.zip from the latest release, unzip, and drag FNSwitcher.app to /Applications.
On first launch, right-click the app → Open to bypass the Gatekeeper warning (the app is not notarized).
Requires macOS 14+ and Xcode.
# Build and create .app bundle
./scripts/build-app.sh
# Or build and run directly
cd FNSwitcher
swift build -c release
.build/release/FNSwitcherThe app runs in the menu bar — no dock icon.
- Click the keyboard icon in the menu bar
- Use Add App... to select which apps should use function keys
- Switch between apps — fn key mode toggles automatically
- Launch at Login keeps it running across restarts
FNSwitcher uses IOKit to toggle HIDFKeyMode on the IOHIDSystem, the same low-level mechanism macOS uses internally. This provides instant switching with no restart required and no special permissions (no Accessibility, no Input Monitoring).
App switches are detected via NSWorkspace.didActivateApplicationNotification. When the app quits, the original fn key mode is restored.
MIT