TidyMacSystem Data is everything macOS doesn’t put in another storage category: Time Machine local snapshots, app caches, iPhone backups, developer files, logs, virtual machines, and hidden folders. It often reaches 100–400 GB. You can’t open it in System Settings, but each part inside it can be measured and explained.
The five questions
Space used by macOS, other user accounts, or folders that even Full Disk Access can't open.
TidyMac shows the total so the numbers add up, and doesn't guess what's inside.
TidyMac can't or won't change this.
How big it gets: 30–400 GB. Reports after macOS 27 mention 290 GB, 357 GB and 400 GB.
What's usually inside
- Time Machine local snapshots: often the single biggest part, and safe to thin. Details
- iPhone and iPad backups: check before removing. Details
- App caches: safe for closed apps. Details
- Developer files: Xcode, simulators, package caches, Docker. Details
- App data: chat apps and browsers in Application Support. Details
For a step-by-step cleanup, read how to clear System Data on macOS 27.
Do it yourself
If this is very large, restarting your Mac lets macOS clear temporary system files on its own.
See your own what tidymac can't see in seconds
Scan free, see every part of your storage explained, and clean only what’s safe. Everything goes to the Trash first.
Frequently asked questions
Is it safe to delete what tidymac can't see on a Mac?
TidyMac can't or won't change this.
Why are my what tidymac can't see so big?
TidyMac shows the total so the numbers add up, and doesn't guess what's inside.
How do I clean what tidymac can't see manually?
If this is very large, restarting your Mac lets macOS clear temporary system files on its own.