WhySlow
What is mdworker on Mac?
Reads the contents of files so Spotlight can search them.
Why is mdworker using so much CPU?
Busy when many new or changed files need indexing.
Should you quit mdworker?
No. mdworker is part of macOS. Quitting it can break things, and macOS starts it again anyway. When it is busy, it usually settles on its own.
Is mdworker a virus?
No. mdworker 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 mdworker 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 mdworker on your Mac
Open Activity Monitor (Applications › Utilities), choose the CPU tab and type mdworker 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 mdworker in plain English and only flags it when it is really slowing your Mac down.
What to do if mdworker stays busy
- Give it time. After a macOS update or a big file copy, Spotlight can index for a few hours. Keep the Mac plugged in and awake.
- Keep busy folders out of the index: open System Settings › Spotlight › Search Privacy and add folders like Xcode DerivedData, Docker data or virtual machine folders.
- If mdworker has been busy for more than three hours, the index is probably stuck. Rebuilding it usually fixes this: WhySlow does it in one click, or run “sudo mdutil -E /” in Terminal.
How WhySlow helps with mdworker
- Shows how much CPU and memory mdworker is using right now, in plain English.
- Opens Spotlight settings so you can keep big folders out of the index.
- Rebuilds the Spotlight index when indexing has been stuck for hours (one-click fix).
- Tells you when mdworker is the real cause of a slow Mac, and when it isn't.
Free to explain. $7 once for one-click fixes.