Sash

A native macOS menu-bar app for snapping and grouping windows into your own custom layouts — up to 9 windows per screen in any arrangement. Drag a window and it snaps into a zone, FancyZones-style. Built in Swift for Apple Silicon / macOS 13+.

sash (noun) — "the framework in which panes of glass are set in a window or door." — Merriam-Webster

Fittingly, Sash is the framework that sets your windows' panes into place.

Prior art & a shoutout to MacsyZones

Sash covers the same ground as MacsyZones by Meowing Cat (rohanrhu) — a mature, open-source macOS zone-snapping app. I built Sash without realizing MacsyZones already existed, and it's the much more developed version: it's been polished over many releases and has extras like Shake-to-Snap and Quick Snapper. If you want a battle-tested tool today, go grab it:

brew install --cask macsyzones

Sash remains a smaller, from-scratch take that I maintain for my own workflow. Big thanks to Meowing Cat for the excellent prior art. 🐈

Features

• Drag-to-snap — arm a layout, then drag any window; zones light up and it snaps into place.
• Custom layout designer — draw your own zones (any 1–9 window arrangement), name them, reuse them.
• Keyboard shortcuts — send the focused window to a zone with a hotkey.
• Menu-bar picker — pick a zone from the menu.
• Per-monitor — arm snapping on one display and leave your other monitors free.
• Esc to cancel a snap mid-drag.
• Hold-⌃ mode — optionally require holding Control to snap, so casual drags are untouched.
• Launch at Login, and a stable app icon.

Drag-to-snap (the main way to place windows)

1. Menu bar ▸ Drag windows into: ▸ pick a layout (or Off).
2. Menu bar ▸ Snap on monitor: ▸ pick the display to snap on (or Any). Your other monitors stay free for manual arranging.
3. Drag any window. The zones appear as a translucent overlay; the one under the cursor highlights. Release to snap it in. Press Esc mid-drag to cancel.

Repeat for each window — drag them one by one into position.

Custom layouts

Menu bar ▸ Custom Setup…

1. Pick the target monitor.
2. Design zones: set Grid (cols × rows) → Generate Grid, or double-click the canvas to add a zone, drag to move, drag the corner to resize. Select a zone to fine-tune X/Y/Width/Height or rename it; Delete removes it. Zones may overlap (e.g. two full-screen zones plus two centered — the "2 full + 2 center-half" arrangement).
3. Name it, then Use for Drag-Snap — it's armed immediately, start dragging windows in. (Or assign windows per-zone from the popups and hit Apply to place them all at once.)

Saved layouts appear in the menu and can be deleted there.

Keyboard shortcuts

Modifier stack: ⌃⌥⌘ (Control-Option-Command)

Shortcut	Action
⌃⌥⌘ ← / →	Left / right half
⌃⌥⌘ ↑	Maximize
⌃⌥⌘ 1–9	Send focused window to zone 1–9 of the armed layout

Snaps apply to the focused window (on the armed monitor, or the screen under the mouse).

Build & run

./scripts/build_app.sh release   # builds, bundles, signs
open build/Sash.app

On first launch, grant Accessibility permission (System Settings ▸ Privacy & Security ▸ Accessibility) — the app can't move other apps' windows without it.

Make the permission stick across rebuilds (optional, run once)

./scripts/make_cert.sh   # creates a stable self-signed code-signing identity

Without this, each rebuild is ad-hoc signed and macOS re-asks for Accessibility. With it, build_app.sh signs with a stable identity so you grant permission just once.

Package as a DMG

./scripts/make_dmg.sh release   # builds the app, then packages build/Sash.dmg

The disk image contains Sash.app and an Applications shortcut — open it and drag Sash onto Applications to install.

Installing from the DMG

Sash is signed ad-hoc (no paid Apple Developer ID), so on a machine that didn't build it, Gatekeeper will warn the first time. To open it anyway:

• Right-click Sash.app ▸ Open ▸ Open (only needed once), or
• clear the download quarantine flag: xattr -dr com.apple.quarantine /Applications/Sash.app

For friction-free distribution you'd need an Apple Developer ID plus notarization.

Tests & coverage

The pure logic (geometry, layouts, persistence) lives in the SashKit target and is fully unit-tested:

swift run SashTests   # runs the suite (works with only Command Line Tools)
./scripts/coverage.sh       # line/region/function coverage for SashKit (100%)

The AppKit/Accessibility glue in the Sash executable is driven by the OS window server and is verified manually rather than unit-tested.

Architecture

Target	What
SashKit	Pure, testable logic: Zone/Layout geometry, coordinate math, layout persistence. No AppKit runtime deps.
Sash	The menu-bar app: window engine (Accessibility API), drag-snap overlay, hotkeys, the Custom Setup window.
SashTests	Dependency-free test runner (runs via swift run).

macOS exposes other apps' windows through the Accessibility API (AXUIElement). Sash reads a window and sets its kAXPosition / kAXSize, translating between AppKit (bottom-left origin) and Accessibility (top-left origin) coordinates. Window ↔ on-screen matching uses the private-but-stable _AXUIElementGetWindow.

License

MIT — see LICENSE.