WhySlow
What is WindowServer on Mac?
Draws every window, animation and display you see.
Why is WindowServer using so much CPU?
Busy with many open windows, external or scaled displays, transparency effects, or an app redrawing nonstop.
Should you quit WindowServer?
No. WindowServer is part of macOS. Quitting it can break things, and macOS starts it again anyway. When it is busy, it usually calms down once its work is done.
Is WindowServer a virus?
No. WindowServer is a genuine part of macOS, signed by Apple and stored in a protected system folder that apps can't change. Malware sometimes borrows familiar names, so if a process called WindowServer lives outside /System or /usr, or you see it after installing something unusual, run a check with a trusted tool and keep macOS up to date.
How to check WindowServer on your Mac
Open Activity Monitor (Applications › Utilities), choose the CPU tab and type WindowServer in the search field. The % CPU column shows how busy it is: 100% means one full processor core. The Memory tab shows how much memory it uses. Activity Monitor shows numbers but doesn't say what they mean; WhySlow explains WindowServer in plain English and only flags it when it is really slowing your Mac down.
What to do if WindowServer stays busy
- Close windows and tabs you aren’t using; every window adds drawing work.
- Turn on Reduce transparency in System Settings › Accessibility › Display.
- If you use external displays at a scaled resolution, try the default resolution in System Settings › Displays.
How WhySlow helps with WindowServer
- Shows how much CPU and memory WindowServer is using right now, in plain English.
- Opens Display settings so you can turn on Reduce transparency.
- Opens Displays settings to check scaled resolutions.
- Tells you when WindowServer is the real cause of a slow Mac, and when it isn't.
Free to explain. $7 once for one-click fixes.