windowctl is the engine. This skill never reaches into Quartz, Win32, X11, or wmctrl directly. Every operation is a single windowctl invocation. If a recipe cannot be expressed as one, it does not belong in this skill.
Always discover before acting. Before any move / focus / resize, run windowctl windows list --json to confirm exactly one window matches the user's filter. --title is a case-insensitive substring; --app is a case-insensitive exact match. Empty strings are rejected (--title cannot be empty). When zero match, surface what was actually open and ask. When many match, list them with IDs + bounds and ask which — the CLI silently picks the first match, which is rarely what the user wants.
Monitors are 1-indexed by ascending (X, Y) origin. The leftmost display is always 1. IDs from monitors list and the per-window Monitor field share the same numbering and are stable across reboots / re-plugs. Use monitors list --json to map heuristics ("the laptop", "the external", "the active one", "where my cursor is") to an integer ID, then pass --monitor <id>. Never hardcode. --monitor 0 is invalid (off-screen sentinel for windows).
Prefer the Focused field for "this window" intents. windows list --json exposes a per-window Focused: true flag; monitors list --json exposes per-monitor Active (cursor) and Focused (frontmost-window centroid). For "snap THIS window" / "what's on my current screen" requests, read these instead of guessing — see references/windows.md WIN-L-6 and references/monitors.md MON-R-4 / MON-R-5.
Zone vs coords are mutually exclusive. --zone and --x/--y/--w/--h cannot be combined. --w and --h must be > 0 in coord mode; both move and resize enforce this.
--monitor changes coord interpretation. With --monitor, raw --x/--y are RELATIVE to that monitor's origin. Without --monitor, they are ABSOLUTE in the global virtual desktop. Get this wrong and the window lands off-screen.
OS clamps surface as exit 1 with details. When the OS or app refuses the requested geometry (Chrome's minimum size, sandbox restrictions, fullscreen-mode windows), move / resize exits non-zero with a message like windowctl: requested 512x640 at (3840,30), OS clamped to 617x616 ... (likely a minimum-window-size constraint). Treat this as soft-failure: the window did move, but not where asked. Surface the message verbatim and stop — do NOT auto-retry. Note: the (X, Y) in that message can be wrong (BUG-13 upstream); trust the Width/Height and re-read with windows list for the authoritative position.
macOS needs Accessibility once per parent process. On the first failed move / resize / focus with Accessibility permission denied, route to references/permissions.md. The only command that triggers the AX prompt is windowctl permissions; everything else returns the denied error without prompting. Re-run the original command after grant.
WCTL_AX_DEBUG=1 is the macOS triage knob. When move / focus reports window <id> is gone from the AX tree, re-run with WCTL_AX_DEBUG=1 and surface the per-PID AX dump from stderr — that names the match rule (title / geometry / single-window) the bridge tried and failed on.
Linux X11 / Wayland is best-effort. On Linux the adapter shells out to wmctrl + xrandr; Wayland is unsupported beyond what wmctrl can fake. Don't promise pixel-exact placement on those.
Don't dump huge window lists. A typical macOS session has 40+ CGWindow entries (menubar agents, system UI). Filter with --title / --app first, or summarize by app + count and offer to expand.
Stop after each successful action. Don't auto-chain ("moved Chrome — would you like me to also move Slack?"). Wait for the next instruction.

Session Context

Held in conversation memory only — no file writes.

monitors:        cached `windowctl monitors list --json` for the session
                 (refresh if user mentions plugging/unplugging a display)
last_match:      the {id, title, app} of the most recently moved/focused
                 window — useful for "move it to the other monitor"
                 follow-ups

If the session ends, the skill re-lists.

Process

Confirm windowctl is on PATH. Missing → npm install -g @muthuishere/windowctl. STOP if missing; do not attempt fallbacks.
Identify the intent and load the matching family file:
- List windows → references/windows.md
- List monitors (incl. ACTIVE / FOCUSED) → references/monitors.md
- Move a window (zone, split, coords) → references/move.md
- Resize a window in place → references/resize.md
- Focus / raise a window → references/focus.md
- macOS Accessibility prompts + AX-bridge debugging → references/permissions.md
- Composite layouts ("split chrome + slack 50/50") → references/recipes.md
Need a zone refresher? → references/zones.md (cheatsheet for 1A..2D and N:M).
Dispatch the documented windowctl command verbatim. Render per the recipe's "User-visible formatting" block.
Stop and wait.

Self-check

Before trusting the skill's routing, validate format integrity:

sh tests/all.sh

Runs:

tests/validate.sh recipe format + cross-references
tests/install-test.sh install/uninstall idempotency

Zero-exit means the catalogue is internally consistent and installable.

Families at a glance

Family	Reference
Windows (list, filter, Focused field)	`references/windows.md`
Monitors (list, ACTIVE / FOCUSED resolution)	`references/monitors.md`
Move (zone / split / coords / multi-monitor / clamp handling)	`references/move.md`
Resize (in-place width/height change)	`references/resize.md`
Focus (raise + activate, "this window" via Focused)	`references/focus.md`
Permissions (macOS Accessibility, `WCTL_AX_DEBUG`)	`references/permissions.md`
Zones (1A..2D + N:M cheatsheet)	`references/zones.md`
Composite layouts	`references/recipes.md`

window-ctl-skill

window-ctl-skill

Core Rules