How macOS actually works

The Library folder, explained

Updated 2026-07-31 · 5 min read

There are three Library folders on a Mac and they do different jobs. Knowing which is which prevents most of the damage people do while cleaning up.

The three Libraries

Path	Scope	Needs admin
~/Library	Just you	No
/Library	Every user on the Mac	Yes
/System/Library	macOS itself	Protected — do not touch

/System/Library is covered by System Integrity Protection and cannot be modified even with sudo. That is a feature.

Inside ~/Library

• Application Support — real app data: databases, projects, plugins
• Containers — sandboxed apps' private worlds, one folder per bundle ID
• Preferences — .plist settings
• Caches — disposable, frequently huge
• Mail, Messages — your correspondence
• Fonts — fonts installed for you only
• Services, QuickLook, Automator — extensions

Why it is hidden

It was visible until OS X Lion. Apple hid it because editing the wrong file breaks apps, and because it is not where your documents belong. The trade-off is that when you legitimately need something in there, everything conspires to keep you out — Finder hides the folder, Spotlight omits the results.

Getting in

Finder's Go menu while holding Option, or ⇧⌘G and type ~/Library. Permanently:

chflags nohidden ~/Library

What is safe to delete

Generally safe: Caches — apps rebuild them. Old folders in Application Support belonging to apps you removed years ago.

Not safe: Containers for apps you still use, Preferences for apps currently running, anything under Mail or Messages unless you have a backup.

Never: anything in /System/Library.

The search problem

Because Spotlight returns almost nothing from ~/Library, the practical effect is that a large and important part of your own disk is unsearchable by default. find, `mdfind

-onlyin`, or an index that does not exclude it are the three ways round that.

Common questions

Can I delete ~/Library/Caches?

Yes. Apps regenerate what they need. Expect some apps to be slower on first launch afterwards.

What is the difference between ~/Library and /Library?

~/Library is yours alone. /Library applies to every user on the Mac and needs admin rights to change.