TidyMacYou can’t clear System Data as one block, because it’s a mix of things. Thin Time Machine local snapshots, remove old iPhone backups you don’t need, clear caches of closed apps, delete old installers, and clean developer files with their own tools. Everything else, including macOS itself, should stay.
- Restart your Mac so macOS can clear temporary system files on its own.
- Thin Time Machine local snapshots with tmutil.
- Remove iPhone and iPad backups you no longer need from Finder › Manage Backups.
- Clear caches of apps that are closed (~/Library/Caches).
- Delete .dmg and .pkg installers for apps you’ve already installed, and old “Install macOS” apps.
- Clean developer files with their own commands: Xcode DerivedData, simulators, npm, Homebrew, Docker.
- Empty the Trash once you’re sure.
What "System Data" actually is
System Settings › General › Storage sorts your disk into Apps, Documents, Photos and a few others. System Data is everything that doesn't fit those boxes. On macOS 27, people have reported it at 290 GB, 357 GB and even 400 GB.
It usually contains, from biggest to smallest:
- Time Machine local snapshots: hourly restore points on your own drive. What they are
- iPhone and iPad backups made with Finder. Where they are
- App data and caches in your Library folder. App caches
- Developer files: Xcode, simulators, package caches, Docker, local AI models. For developers
- macOS itself, including Apple Intelligence models, which you can't remove. How big it is
Step 1: Restart first
A restart lets macOS delete swap files and some temporary system data. It's free and occasionally recovers several gigabytes on its own.
Step 2: Thin Time Machine local snapshots
This is often the single biggest win. It doesn't touch your backups on an external drive.
tmutil listlocalsnapshots /
sudo tmutil thinlocalsnapshots / 999999999999 4The second command asks for your password. More about snapshots
Step 3: Remove old device backups
Open Finder, select any connected device (or use TidyMac, which lists every backup with its device name and date), click Manage Backups, and delete backups of devices you no longer have or that back up to iCloud.
Let TidyMac do this for you
Scan free, see every part of your storage explained, and clean only what’s safe. Everything goes to the Trash first.
Step 4: Clear caches of closed apps
Quit the apps first. Then in Finder choose Go › Go to Folder, type ~/Library/Caches and move the folders of the biggest apps to the Trash. Skip com.apple.* folders you don't recognise, and remember music apps may keep offline downloads there.
Step 5: Delete old installers
Sort Downloads by Kind and remove .dmg and .pkg files for apps you've already installed. Check Applications for Install macOS apps; each is 12–15 GB.
Step 6: Developer files, with their own tools
rm -rf ~/Library/Developer/Xcode/DerivedData/*
xcrun simctl delete unavailable
brew cleanup -s
npm cache clean --force
docker system pruneUse ollama rm for local AI models you no longer use.
Step 7: Empty the Trash
Files you moved to the Trash still use space. Empty it once you're sure nothing you need is in there.
What not to delete
The faster way
TidyMac does steps 2 to 6 with one review screen: it measures each part, explains it in plain English, ticks only what's safe, and moves everything to the Trash first.