Standalone ers

ers can run independently of tarmac. It borders all on-screen windows (or a specific window) and responds to focus changes.

Installation

Via Homebrew:

brew tap gardesk/tap
brew install ers

From source:

cargo install --git https://github.com/gardesk/ers

Usage

ers [OPTIONS] [WINDOW_ID]

Run with no arguments to border all windows:

ers

Stop with Ctrl-C. All overlays are cleaned up on exit.

Options

Flag Default Description
-w, --width <PX> 4.0 Border width in pixels
-r, --radius <PX> 10.0 Corner radius
-c, --color <HEX> #5294e2 Active (focused) border color
-i, --inactive <HEX> #59595980 Inactive border color
--active-only off Only show border on the focused window
--list — List on-screen windows with IDs and bounds, then exit
-h, --help — Show help

Examples

Default borders on all windows

ers

Custom colors and width

ers --width 6 --color '#ff6600' --inactive '#33333380'

Active window only

ers --active-only --width 3 --color '#00ff00'

Border a specific window

ers --list                    # find the window ID
ers 1234                      # border window 1234 only

With a custom radius

ers --radius 0                # square corners
ers --radius 20               # very rounded

Debug logging

RUST_LOG=debug ers

This prints detailed information about window events, border creation/destruction, and focus changes.

Using with other window managers

ers doesn't depend on tarmac. You can use it with any macOS window manager (yabai, AeroSpace, Amethyst) or with no window manager at all. Just run it and it'll border whatever windows are on screen.

macOS Tahoe notes

ers was developed on macOS Tahoe and accounts for several undocumented behaviors of the SkyLight APIs on that version:

  • SLSCopyManagedDisplaySpaces corrupts window creation on all connections — ers avoids this call
  • Each overlay requires its own SLS connection
  • Windows must be created at their final size (the 1x1-then-reshape pattern doesn't work)
  • Drawing must happen before setting window tags

These constraints were discovered through trial and error. If ers stops working on a future macOS version, these are the likely breakage points.