MonitorControl

MonitorControl is the answer to "why can't my Mac's brightness keys touch my external monitor" for people who would rather not pay for one. It sends DDC commands for brightness, contrast and volume, uses Apple's native protocol on Apple displays, and draws the real macOS on-screen overlay while doing it, so it reads as a system feature rather than a third-party slider bolted on top.

It is MIT licensed and genuinely free — no pro tier, no nag screen, no unlock. Install it from GitHub releases or Homebrew, grant the permissions it asks for, and point your existing brightness keys at it.

What you give up against Lunar is the clever layer: no ambient-light curve, no time-of-day schedule, no dimming tricks beyond the gamma fallback. You also give up support. There is an issue tracker and nothing else, so when a new macOS breaks something you wait for a volunteer release — the project already names the minimum build required for macOS 27.

Try this before spending money on the category. If your monitor answers DDC and all you want is working brightness keys and a volume slider, this is the whole job done for nothing, and the paid apps only start to make sense once you want automation.