Is it safe to delete ~/Library/Caches on a Mac? Mostly, and here is the list of what is not a cache

Every "clean your Mac" guide ends with the same step: open ~/Library/Caches and delete everything. It is not wrong. It is also usually not where your space went, and the same guides then send people into neighbouring folders where the advice stops being safe.

The rule

A cache is something the app can rebuild without you. If you can name what will recreate a file, it is a cache. If you cannot, it is not, whatever the folder is called.

~/Library/Caches is the folder macOS reserves for the first kind, and apps mostly respect it. Safari's page cache, Spotify's downloaded audio, Xcode's module cache, Slack's image cache. Delete them and the app fetches them again.

Doing it

Quit the apps whose caches you are clearing. An app that is running will keep writing into a folder you just deleted, or crash when it reaches for a file that was there a second ago.

# Biggest first, so you know what you are deleting.
du -sh ~/Library/Caches/* 2>/dev/null | sort -rh | head -20

Then delete the contents of the folders you recognise, either in Finder or with rm -rf ~/Library/Caches/<name>. Leave ~/Library/Caches itself in place. Some apps fail to start if their cache directory does not exist and do not know how to recreate it.

/Library/Caches (no tilde) is the system-wide version and holds the same kind of thing for system services. It needs an administrator password to touch and is rarely large.

The folders that are not caches

These sit next to Caches in ~/Library, get deleted by people following the same instinct, and cost real data:

Folder	What is in it
Application Support	Local databases, saved state, message history, licenses
Containers and Group Containers	The same, for sandboxed apps: WhatsApp chats, Notes, Mail
Mail	Your email, for POP and many IMAP setups
Keychains	Every saved password
Mobile Documents	Your iCloud Drive, the only local copy
Preferences	Every app's settings
Cookies and HTTPStorages	Logins for every website

Application Support and Containers are the ones that catch people, because some apps do store caches inside them. The way to tell is to look at the subfolder names: Cache, Code Cache, GPUCache, CachedData inside an app's container are caches. Data, Documents, Library/Application Support inside it are not.

Why it did not help much

On a developer's Mac ~/Library/Caches is often 5 to 15 GB while the folders next to it hold ten times that: ~/Library/Developer for Xcode and simulators, ~/Library/Containers/com.docker.docker for Docker, ~/Library/Application Support/MobileSync for iPhone backups. Each of those has its own page here.

Where Decruft fits

Decruft applies the rule above in code. Folders under ~/Library/Caches, package-manager stores, logs and saved state are labelled safe. Application Support and the container folders are labelled review-first with a note on what each holds, and the seven folders in the table are refused outright, by a guard that denies anything it does not recognise as junk. Everything it does remove goes to the Trash.