K380 Fn

A tiny native macOS menu-bar app that keeps a Logitech K380 (including K380 for Mac) in function-keys-primary mode.

Out of the box the top row is media / “smart” keys; F1–F12 need Fn. Logitech Options can invert that. This app sends the same short HID++ output report to the keyboard and keeps sending it, because the firmware does not remember the setting. It reverts after power-off, Easy-Switch, sleep/wake, or Bluetooth glitches.

There is no Dock icon. Control it from the Fn item in the menu bar. Finder and System Settings show a cream Fn app icon.

No Logitech software, no hidapi, no Karabiner, no hidutil, no network.

Works with:

Keyboard	USB/Bluetooth ID
K380	046D:B342
K380 for Mac	046D:B362

Any Logitech HID device whose product name contains K380 is also matched.

Languages: English (default) and Português (Brasil). Follows the Mac’s first preferred language, or pick one in Settings.

Requires macOS 13+ (Apple silicon or Intel).

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Regarding AI usage

This app was written with AI assistance (vibe coded 🦾🤖). It is provided as-is, with no warranty — review the source and the HID report bytes yourself before trusting it with your keyboard.

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Install from this repo

You need Xcode Command Line Tools:

xcode-select --install

Then, in the project folder:

./scripts/build.sh
open dist/K380Fn.app

build.sh will:

1. Run tests (./scripts/test.sh; skip with SKIP_TESTS=1)
2. Compile with swiftc (not SwiftPM — some Command Line Tools installs cannot load Package.swift)
3. Wrap dist/K380Fn.app and ad-hoc codesign it (com.github.cobalto.k380fn)
4. Quit any running K380 Fn and reset Input Monitoring for this bundle (tccutil reset ListenEvent com.github.cobalto.k380fn)

Skip the quit/reset with SKIP_RESET=1 ./scripts/build.sh if the current build is already authorized and you only changed UI.

Package.swift is only for opening the folder in Xcode. Day-to-day builds are ./scripts/build.sh.

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First launch (Input Monitoring)

macOS will not let the app talk to the keyboard until Input Monitoring is granted to this exact .app.

1. Connect the K380 over Bluetooth and select this Mac’s Easy-Switch slot.
2. open dist/K380Fn.app — look at the right of the menu bar for Fn.
3. Click Allow on the Input Monitoring prompt. (If you click Don’t Allow, HID will fail until you reset — see below.)
4. System Settings → Privacy & Security → Input Monitoring
   • Turn on K380 Fn.
   • If you see two K380 Fn rows, enable the one whose path is
     …/K380-FunKit/dist/K380Fn.app
     A copy in Applications is a different app. Toggling that one does nothing for dist/.
5. Optional: allow notifications (failures only, never success).
6. Menu: Enable F-keys primary if it is not already on, or Re-apply now.

F1–F12 should work without Fn; media keys should need Fn.

After every rebuild

Ad-hoc signing is a new Input Monitoring client each time the binary changes. ./scripts/build.sh resets TCC for you. Then:

open dist/K380Fn.app

Click Allow, and enable the dist row again if macOS lists more than one K380 Fn.

Reset without rebuilding (quits the app):

./scripts/reset-permissions.sh
open dist/K380Fn.app

In Settings: Forget Input Monitoring permission… runs the same tccutil reset (it removes the app from the list). Use Re-apply now on the menu if the keyboard is merely stuck.

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Using the app

Menu bar: Fn plus a status mark (filled = F-keys on, hollow = off, × = no keyboard, lock/warning = permission or write error). Settings can switch the mark to short text (On / Off). Hover for a longer explanation.

Click Fn:

• One status line
• Enable / Disable F-keys primary
• Settings…
• Quit K380 Fn
• Re-apply now (always): send the HID report again, no System Settings changes
• When permission is missing: Open Input Monitoring…

Settings

• F-keys primary, Launch at Login, glyph vs text, language
• Copy a diagnostics report (for GitHub issues)
• Input Monitoring / re-apply / permission reset
• About tab

Launch at Login uses SMAppService (no Apple Developer account). You can also add dist/K380Fn.app under System Settings → General → Login Items — use the same copy you authorized.

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Check that it works

• F-keys primary: F1–F12 without Fn; media needs Fn.
• Turn the keyboard off and on, or Easy-Switch away and back: the mode should return by itself.
• Sleep/wake the Mac: same.
• Disable F-keys primary: factory-like media row; enable again.

Logs:

log stream --predicate 'eventMessage CONTAINS "K380Fn"' --style compact

A good write looks like SetReport ... -> 0x00000000.

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Troubleshooting

What you see	What it usually means	What to do
Input Monitoring required	macOS blocked IOHIDManagerOpen (0xe00002e2). The switch in Settings is for a different signature or path.	Quit the app. ./scripts/reset-permissions.sh then open dist/K380Fn.app. Click Allow. Enable the dist row, not Applications.
Waiting for K380	No matching HID device (Bluetooth off, wrong Easy-Switch slot, or keyboard asleep).	Pair the K380; press this Mac’s Easy-Switch key; power-cycle the keyboard.
Write failed / retrying	Device seen but the report was rejected (often right after connect).	Wait a few seconds; Re-apply now.
Two K380 Fn in Input Monitoring	dist/ vs /Applications/ (or an old rebuild).	Authorize the path you actually open.
Top row still media after “applied”	Wrong Easy-Switch device, or Options+ fighting the same report.	Confirm this Mac is the active slot. Quit Options+ if it is installed.

Copy report for GitHub in Settings pastes version, status, and recent HID lines.

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Protocol (for the curious)

HID++ 1.0 output report, report ID 0x10:

Mode	Bytes
F-keys primary	10 FF 0B 1E 00 00 00
Media primary	10 FF 0B 1E 01 00 00

Tried as 7 bytes (including report ID) then 6 bytes (without), on every matching K380 collection until one write succeeds. Retries with backoff after attach; re-applies about every 15 seconds and on wake.

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License

Use and share freely. Not affiliated with Logitech.

Source: https://github.com/cobalto/k380fn