1
Arrange
Choose Arrange & Line Up… from the menu bar and drag the tiles roughly where your screens sit. Big numbers appear on each real screen so you know which is which.
The problem
Screen alignment in System Settings is a lot of trial and error, and it's never perfect.
In Displays › Arrange you drag two tiny rectangles, then move the pointer across to check. Too high. Nudge it. Too low. Nudge again. There's no way to see where the screens really meet, so it's trial and error every time.
In System Settings
Drag a tile, test the pointer, drag again. The tiles are tiny, so even a small drag moves the screen a long way on your desk.
With Shim
Shim draws lines across your real screens. Drag until they run straight, click Done, and the arrangement is exact the first time.
How it works
One try is all it takes. Just make the lines straight.
Shim draws one continuous pattern across your real screens. Where it breaks at the gap, you drag it until it doesn't.
↕ drag until the lines continue
2
Line Up
Lines appear across all your screens. Drag a screen's lines, or nudge with the arrow keys, until they run straight across the gap.
3
Done
Shim writes the macOS display arrangement on the spot and saves the layout for this exact set of screens. Plug them in again tomorrow and it's already right.
Features
Set it once. Forget it's there.
Remembers every desk
Home, office, the conference room projector. Each set of screens gets its own layout, re-applied when you reconnect or wake.
Any mix of sizes
Laptop and 27-inch, Retina next to non-Retina, portrait next to landscape. If the pixels don't match the inches, Shim lines them up.
Handles mystery screens
Some TVs and projectors don't report their size. Pick it from a list and carry on.
Lives in the menu bar
Launches at login and stays out of the way. A notification asks once when it sees a new set of screens.
Never fights you
Shim only acts on reconnect or wake. Change the arrangement in System Settings and it leaves your choice alone.
Sandboxed & private
A sandboxed Mac App Store app with no network access and no data collection. Your layouts stay on your Mac.
Privacy
Shim collects nothing.
Data Not Collected
Shim makes no network connections. Your screen layouts are saved only inside Shim's sandbox on your Mac, and nothing leaves it.
FAQ
Questions
What do I need to run Shim?
A Mac running macOS 26 or later, with two or more displays connected. With one screen or mirrored screens, Shim's menu explains why there's nothing to arrange.
What does Shim actually change?
The macOS display arrangement — the same setting as System Settings › Displays › Arrange. It just sets it far more precisely than dragging rectangles by eye.
Can I undo it?
Cancel in Line Up changes nothing. After that, you can rearrange in System Settings › Displays any time, and Shim won't override it unless you reconnect those screens with Re-apply on Reconnect turned on.
Do I need to measure my screens?
No. You line up the pattern by eye on the real screens; Shim works out the arrangement from that. For screens that don't report a size, you pick one from a list.
What about three or more screens?
Arrange and Line Up work with every connected screen, and the layout is saved for that exact combination.
Still stuck? Email [email protected].
