The short version: Rectangle normally snaps a window on the display that window is already sitting on, not the one your cursor is on. If that feels backwards to you, switch it to follow the cursor in Rectangle’s settings. One setting, and most wrong-monitor complaints disappear.
Why it picks the screen it picks
Every window command needs a target screen, and with two monitors there are two defensible answers: the screen holding the window, or the screen holding the pointer. Rectangle defaults to the window.
That default is right for keyboard-first work. You Command-Tab to an app, press Left Half, and the window arranges itself where it already is, regardless of where you happened to leave the mouse. Nothing jumps across displays because your pointer drifted.
It’s wrong for mouse-first work. If you think of the cursor as marking where your attention is, you expect the window to come to you, and instead it snaps neatly into place on a monitor you’re not looking at.
Neither behavior is a bug, which is why this rarely gets diagnosed. People assume something is broken when the app is doing exactly what it was told, using a rule that doesn’t match their habits.
The fix
Open Rectangle’s settings from the menu bar icon and find the option controlling which screen counts as current. Set it to use the display containing the cursor. Test it right away: put your pointer on the second monitor, focus a window on the first, press Left Half. The window should now land under your pointer.
Give it a few days before deciding. This setting rewires a reflex, and the first day of either behavior feels wrong if you’ve built habits around the other. The clearest signal is which screen you look at while pressing the shortcut. If your eyes are already on the destination, cursor-based wins.
When the arrangement itself is wrong
A separate failure looks identical from the outside: windows land on the correct display, but the wrong side of it, or throw shortcuts move them in a direction that makes no sense.
Open System Settings → Displays and look at the arrangement diagram. macOS positions displays in a virtual coordinate space, and that space decides what “next display” means. If the diagram shows your external monitor to the left of the laptop while it physically sits on the right, every directional command runs backwards. Drag the display icons until the diagram matches your desk.
Vertical stacking catches people the same way. Monitor mounted above the laptop, arranged side by side in the diagram, and the throws feel arbitrary until you fix the arrangement.
After any change to that arrangement, quit Rectangle and reopen it. Screen geometry is calculated on launch, and a stale calculation from a previous layout produces exactly the kind of confident, wrong placement that sends people looking for a bug report. Same applies after plugging in a new monitor or changing resolution.
Clamshell mode and the vanishing display
Working with the lid closed changes the display set, and that changes what throw shortcuts can do. The built-in screen leaves the arrangement entirely, so next-display commands cycle only through connected externals. With a single external monitor, there’s no second display to move to, and the shortcut does nothing at all.
That produces one of the more confusing reports I get. The shortcut worked yesterday with the lid open, does nothing today with it closed, and nothing about Rectangle changed. There’s nowhere to throw the window.
Opening and closing the lid mid-session is worth a Rectangle relaunch too, since displays appear and disappear from the arrangement as you do it.
What happens when a monitor disconnects
Unplug an external display and macOS relocates its windows to whatever screen remains, usually resized and rarely in an arrangement you’d have chosen. That’s the system’s doing, not Rectangle’s, and no window manager prevents it.
What you can do is rebuild quickly. Reconnect, then reapply your layout shortcuts. On the free version that’s a few keystrokes per window, which is the whole reason for having shortcuts in the first place. Rectangle Pro can restore a saved layout in one step, and if you dock and undock several times a day, that feature alone tends to justify it.
If your snap areas also stopped appearing after a display change rather than just misplacing windows, that’s a different symptom with its own causes, covered in the snap areas guide.
Frequently asked questions
How does Rectangle decide which monitor to snap a window to?
By default it uses the display that already contains the window being acted on, so a half-screen command keeps the window where it is. Rectangle can instead use the display containing the cursor, which changes the result whenever your pointer and the focused window are on different screens.
Why do my windows move to the wrong screen only sometimes?
Because the two possible answers agree most of the time. When the cursor sits on the same display as the window, both rules produce the same result. The mismatch only appears when you leave the pointer on one screen while a window on another screen holds focus.
Where do my windows go when I disconnect a monitor?
macOS moves them to a remaining display, usually resized to fit and rarely in the arrangement you had. Rectangle doesn’t control that behavior. Reapplying your layout shortcuts after reconnecting is the practical fix, and Rectangle Pro can restore a saved layout in one step.
Do throw shortcuts work with the laptop lid closed?
They work, but the set of displays changes. In clamshell mode the built-in screen isn’t part of the arrangement, so next-display commands cycle only through connected external monitors. With one external monitor, those shortcuts have nowhere to send a window and appear to do nothing.