---
name: screendark
description: Control ScreenDark on macOS to adjust, darken, or restore built-in and external displays without intentionally locking the current session. Use when the user asks to change a Mac display's visual brightness, set one or all displays to black, restore dark displays, or recover the screen with the ScreenDark shortcut.
---

# ScreenDark

Operate ScreenDark only after the user explicitly asks to change a display. Treat darkening as a visual Gamma state, not a security lock or physical power state.

## Adjust or darken a display

1. Check that ScreenDark is installed. If needed, launch it with `open -b com.liuzhuang.thanoslight`.
2. Open the `ScreenDark` menu bar item.
3. Identify the requested built-in or external display.
4. Click or drag across that display's device preview to set the requested brightness. Set it to `0%` only when the user asks for a black screen.

If the user asks to darken every display, confirm the fixed recovery shortcut before setting the last visible display to `0%`.

ScreenDark requests both `.idleSystemSleepDisabled` and `.idleDisplaySleepDisabled` only while at least one display is at `0%`. The display-sleep request is system-wide, so one display at `0%` keeps every display awake at the system level. Brightness values from `1%` to `99%` do not trigger those requests. ScreenDark does not actively lock the Mac or disable the screen saver, so manual lock, the screen saver, app state, permissions, and capture paths still determine whether other work continues.

## Restore displays

- Restore one display by opening ScreenDark and moving that display above `0%`, or use its configured shortcut.
- Restore all system Gamma and set every ScreenDark display state to `100%` with `Control-Option-Command-B`.
- Use the recovery shortcut immediately if the visible state is uncertain.

## Guardrails

- Never describe ScreenDark as locking or securing the Mac.
- Never describe `0%` as powering off the display or backlight.
- Never promise that ScreenDark keeps every task, browser action, or remote session running.
- Do not change macOS screen saver, automatic lock, or sleep settings unless the user separately requests it.
- Do not invent a download URL. If the app is missing, ask for the source folder and run `bash reinstall.sh` from its root.
- Report that external displays must support macOS Gamma adjustment when a display does not respond.