Brisync is a free, open-source macOS menu-bar utility that keeps external monitor brightness in sync with your MacBook's built-in display as ambient light changes — no manual slider-dragging required.
What is Brisync?
Brisync is a lightweight macOS daemon that mirrors your MacBook's automatic brightness adjustments to connected external displays in real time. When macOS detects a change in ambient lighting and dims or brightens the internal panel, Brisync intercepts that event and pushes the equivalent brightness level to any compatible external monitors attached over USB-C, Thunderbolt, or DisplayPort.
It lives quietly in the menu bar, consumes almost no CPU, and asks for nothing beyond Accessibility permission to read the system brightness sensor. There is no subscription, no account, and no telemetry — it is plain, honest open-source software.
What does Brisync do best?
Brisync eliminates the single most annoying friction point of working with a multi-display Mac setup: stepping into a bright room and watching your laptop adjust while your external monitor stays blindingly bright, or vice versa. Once configured, the experience collapses into invisibility — you simply stop thinking about brightness.
- Passive operation: no keyboard shortcut to remember, no widget to poke. It hooks into the same ambient light readings macOS already takes and acts automatically.
- Multi-monitor support: if you run two external displays, Brisync adjusts both simultaneously, keeping the whole desk coherent.
- Offset control: a small preference lets you set a fixed brightness offset per display, which is invaluable if your external panel is just inherently dimmer or brighter than the built-in Retina screen at equivalent settings.
- Zero background chatter: unlike some commercial alternatives that poll on a timer, Brisync reacts to actual system events, so it is not burning cycles when nothing is changing.
Is Brisync free?
Yes — Brisync is completely free to download and use. The project is hosted on GitHub under an open-source licence, so you can inspect every line of code, build it yourself, or contribute a fix. There is no paid tier, no premium unlock, and no in-app purchase. Installation is available via Homebrew Cask, making it a one-liner for anyone already in the terminal.
Who should use Brisync?
Brisync is squarely aimed at Mac users who work at a desk with at least one external monitor and move between different lighting environments during the day — a home office with afternoon sun blazing through the window, a corporate open-plan that dims its overheads in the evening, or a coffee shop with wildly inconsistent natural light.
It is especially compelling for developers and writers who spend long hours in front of the screen and are sensitive to eye strain. If you have ever found yourself squinting at your external display while your laptop panel has already tastefully dimmed itself, Brisync solves that problem permanently. It is not for users whose workflow demands fine per-display brightness control at all times — the automation hands that control to the sensor, which is a trade-off worth acknowledging.
How does Brisync compare to alternatives?
The main commercial competitors in this space are MonitorControl and Lunar. MonitorControl is the closest philosophical sibling — also open-source, also free, but it layers in a broader feature set including volume control via DDC and full manual sliders. If you want that breadth, MonitorControl is excellent. Brisync, by contrast, is deliberately minimal: it does the sync job and nothing else, which makes it faster to set up and easier to trust when something goes wrong.
Lunar is the power-user's choice — adaptive algorithms, hotkey profiles, per-app overrides, beautiful UI — but it carries a paid Pro tier for its best features and a correspondingly larger attack surface for bugs. For someone who simply wants ambient sync without configuration overhead, Brisync wins on simplicity every time.
Apple's built-in "Automatically adjust brightness" setting in System Settings only affects the internal display; it has never extended to external monitors natively. Brisync closes that gap until Apple decides to address it in a future macOS release.
What are Brisync's known limitations?
Brisync works via DDC/CI commands to communicate with external displays, which means monitor compatibility matters. Most modern displays from Dell, LG, and BenQ respond correctly, but some budget panels or certain USB-C docking configurations block DDC commands entirely. If your external display is not responding, check whether DDC is enabled in its on-screen menu — it is usually under a "USB" or "Input" section. Apple Studio Display and Pro Display XDR are controlled through a separate Apple protocol and may behave differently. The project's GitHub issues page is the best place to check for your specific model before committing.
