Fluor is a free, open-source Mac utility that automatically switches the function-key row between media controls and F1–F12 keys depending on which app is in the foreground — no manual toggle required.
What is Fluor?
Fluor is a lightweight menu-bar app that watches your active application and silently reassigns your keyboard's fn-key row to match. If you spend most of your day in Xcode or a terminal, you probably want raw F-keys at your fingertips. The moment you tab over to Spotify or adjust your display brightness, you want the media/brightness/volume keys back. Fluor handles that handoff automatically, the instant focus changes.
The app lives entirely in the menu bar — no dock icon, no sprawling preferences window. You configure a rule per app once, then forget Fluor exists. That invisibility is its greatest achievement.
What does Fluor do best?
Fluor excels at eliminating the fn key dance — that habit of pressing fn every time you switch contexts — which turns out to be a surprisingly significant friction point over a full workday. Once you wire up a handful of rules, your keyboard just behaves correctly everywhere, with no conscious thought on your part.
Setting up rules is genuinely fast. Click the menu-bar icon, choose an app from the list of running processes, and set its fn-row preference to one of three states: always function keys, always media/hardware keys, or follow the system default. That covers every real-world case I've encountered across months of daily use.
I personally have Xcode, iTerm2, and VS Code locked to raw F-keys, while everything else defers to macOS's global preference (media keys). Switching between a debugging session and a browser no longer requires any thought. The transition is immediate — sub-100ms, imperceptible.
Is Fluor free?
Yes — Fluor is completely free to download and use, with no paywalled tiers, no subscription, and no nag screens. It is open-source under a permissive licence on GitHub, which means the code is auditable and community contributions are welcome. You can install it via Homebrew Cask (brew install --cask fluor) or by downloading the release directly from the GitHub repository.
Who should use Fluor?
Fluor is indispensable for developers, power users, and anyone who splits time between creative apps and productivity apps. If you only ever use one type of software you probably don't need it — but the moment you're context-switching between a code editor demanding F5/F8/F12 and a DAW or video editor expecting dedicated transport keys, Fluor pays for itself (in zero dollars and zero seconds of setup time) on the first day.
It is also worth noting that Fluor is particularly valuable on MacBooks, where the Touch Bar or the condensed function-row layout makes per-key conflicts even more annoying. Desktop Mac users with extended keyboards who use BetterTouchTool or Karabiner-Elements for more complex remapping may find those tools already cover this need — but Fluor is far simpler to configure for the specific use case of per-app fn-row mode.
What are the best Fluor alternatives?
The closest alternative is Karabiner-Elements, which is extraordinarily powerful but requires JSON config files and a steep learning curve — overkill if all you want is per-app fn-row switching. BetterTouchTool can replicate Fluor's behaviour as part of a much larger feature set, but it costs money and demands configuration time. Keyboard Maestro can script similar rules but is aimed at macro automation, not keyboard-layer management. For the narrow problem Fluor solves, nothing beats it for simplicity-to-effectiveness ratio.
How does Fluor compare to Karabiner-Elements?
Karabiner-Elements rewires keyboards at the kernel level and can remap any key to any other key — it is the nuclear option. Fluor only toggles the fn-layer mode, which means it works entirely in user space, requires no kernel extensions, installs in seconds, and carries essentially zero risk of breaking other keyboard behaviour. If your only need is context-aware fn keys, Karabiner is heavy artillery for a job that Fluor handles with a scalpel.
