How to delete System Data on Mac (and what not to touch)

How do I delete System Data on my Mac?

The short answer

You can't delete System Data in one go, because it isn't one thing. It's a label for dozens of folders. Most of the big ones are caches, build files and Time Machine snapshots that are safe to clear and come back on their own. A few are your data in disguise: browser profiles, chat history, app settings. Those stay.

Safe to clear

Empty the Trash, then restart. Nothing moved to the Trash is freed until it's emptied, and a restart clears memory swap and temporary files.
App caches. Quit the app first, then clear its folder inside ~/Library/Caches. Each app rebuilds what it needs.
Old iPhone and iPad updates in ~/Library/iTunes/iPhone Software Updates. Nothing needs them once the update is installed.
Xcode build folders in ~/Library/Developer/Xcode/DerivedData. The next build is slower once. More on Xcode →
Time Machine local snapshots. List them with tmutil listlocalsnapshots /. macOS removes them on its own when it needs room; to remove one now:
```
sudo tmutil deletelocalsnapshots 2026-09-21-101500
```
using a date from the list.

Leave these alone

Anything in /System or /private/var. macOS protects most of it anyway, and what it doesn't protect it needs.
~/Library/Application Support as a whole. It holds your browser logins, chat history and app settings. Clear caches, not data.
Docker's disk file. Deleting it by hand destroys every container. The safe way →

A "System Data cleaner" that deletes whole folders will eventually delete something you needed. The safe rule is: only remove things that rebuild themselves.