The short version: Rectangle should sit near zero percent CPU when you aren’t moving windows, with a memory footprint in the tens of megabytes. Sustained CPU with nothing happening on screen is real and almost always means a second window manager is running alongside it. Everything else on this page is how to tell those two situations apart.
What the app actually does when idle
Rectangle waits. It listens for a shortcut and it watches for a window being dragged near an edge, and between those events it does no work at all. There’s no background indexing, no sync loop, no polling of window positions on a timer.
So the expected reading is a flat zero, with a brief spike each time a window moves. Those spikes are the app doing its job and they’re over in a fraction of a second.
Which sets up the most common false alarm on this topic.
The Activity Monitor trap
You suspect Rectangle, so you open Activity Monitor and search for it. There it is, showing a number that isn’t zero.
Opening Activity Monitor means launching an app and focusing a window. That’s precisely the moment Rectangle wakes up and does something. The reading you caught is a reading of you looking.
Leave the window alone for sixty seconds and watch the number instead of the instant it appears. It should fall to zero and stay there. If you want a cleaner test, sort by CPU and see whether Rectangle even stays on the first screen of processes; on an idle Mac it won’t.
Memory works the same way. A few dozen megabytes looks alarming in isolation and is unremarkable for a menu bar app, most of which is system frameworks loaded by anything with a user interface. Compare it against a single browser tab before drawing conclusions.
When it’s genuinely wrong
Three patterns are worth acting on.
Sustained CPU with nothing on screen changing. Not a spike, not the moment you opened Activity Monitor, but a steady number over a minute of not touching anything. That’s real.
Memory that only climbs. Normal usage rises and falls a little. A figure that grows through the day and never comes back down suggests something is accumulating.
Rectangle in the energy report. macOS lists apps using significant energy, and a correctly behaving Rectangle has no business appearing there.
The cause, most of the time
Two window managers running at once. Rectangle moves a window, the other tool notices the change and repositions it, Rectangle sees that and responds, and the loop runs until you quit one of them.
People end up in this state without meaning to. Raycast ships window management enabled by default and gets installed for its launcher. Magnet or BetterSnapTool stays on the system after someone tries Rectangle and forgets to remove the old one. Anyone experimenting with yabai or Amethyst has a tiling engine that actively wants to control every window on screen.
Check what’s running, pick one to own window management, and quit or uninstall the other. The loop stops immediately, which also makes this easy to confirm: quit the suspected tool and watch the CPU number drop while you’re still looking at it.
Two smaller causes
A stuck internal state occasionally survives a display change or a wake from sleep, where the app is recalculating against geometry that no longer exists. Quit Rectangle from the menu bar and open it again. Thirty seconds, and it clears cases that look far more serious than they are.
An outdated version is worth ruling out next, particularly after a macOS upgrade. Compatibility work lands in releases after each system update, and running an old build against a new macOS is a reasonable way to end up with behavior nobody else is reporting.
If neither helps, reinstall properly rather than dragging a new copy over the old one. Remove the app and its preferences file, then install fresh; the clean uninstall guide has the sequence, and skipping the preferences file is how people reproduce the same problem on a fresh install.
When it isn’t Rectangle at all
Worth saying plainly, because a menu bar utility is an easy thing to blame. If your Mac feels slow and Rectangle is idling at zero, the cause is elsewhere: sort Activity Monitor by CPU and look at what’s actually at the top. Spotlight reindexing after an update, a browser with a heavy tab, or a backup running in the background will each outweigh every menu bar app you have combined.
The reverse case is more interesting. If windows feel sluggish specifically when Rectangle moves them, and CPU stays low throughout, that’s not a resource problem. Some apps resize slowly because of how they redraw their own content, and Adobe applications are the ones people notice, with their own reasons for ignoring or resisting window commands.
Frequently asked questions
How much CPU should Rectangle use?
Essentially none while idle. The app waits for a keystroke or a drag and does nothing in between, so a reading near zero percent is expected. Brief spikes when a window is being moved are normal and last a fraction of a second.
Why does Rectangle show high CPU right when I look at Activity Monitor?
Opening Activity Monitor involves moving and focusing a window, which is exactly when Rectangle does work. The reading you catch in that first moment reflects the act of looking. Watch the process for a minute while leaving windows alone to see its real idle behavior.
Is a few dozen megabytes of RAM normal for Rectangle?
Yes. A menu bar app on modern macOS carries system frameworks that account for most of that footprint, and the figure is unremarkable next to a browser tab. Memory that climbs steadily over hours without falling back is the pattern worth investigating.
Can Rectangle drain my battery?
Not under normal operation, because an idle app consumes almost no energy. If Rectangle appears in the significant energy use list, something is keeping it active continuously, most often another window management tool responding to its changes in a loop.