What's safe to delete on a Mac?

Whatever recreates itself: the Trash, installers of apps you already installed, app caches, old logs and developer build data and caches. Deleting them loses nothing.

What should I never delete on a Mac?

System folders, your Photos library as a file, data of apps you still use in Application Support, and anything you can't identify.

How do I free up space on a Mac without losing files?

Delete what recreates itself first, then decide on big recoverable things (backups, simulators, models), and move your own files to an external drive or iCloud instead of deleting them.

How to free up space on your Mac without deleting anything important

In short

The rule that keeps you safe: first delete what recreates itself (caches, build data, old installers), then decide on big things you could get back (backups, models, simulators), and touch your own files last, ideally moving them instead of deleting them.

The one rule: does it come back by itself?

Before deleting anything, ask: if I delete this, will something make it again? A browser cache, Xcode's build data or Homebrew's downloads come back on their own when needed: deleting them is safe. Your photos, documents or an app's database don't: deleting them is forever.

Almost every “I lost something cleaning my Mac” story comes from skipping this question.

Start with what macOS already offers

In System Settings → General → Storage you'll find recommendations worth turning on:

Store in iCloud: files and photos already in iCloud only stay on the Mac when you use them.
Optimize Storage: removes Apple TV movies and shows you already watched.
Empty Trash Automatically: deletes what's been in the Trash for 30 days.

Then, what recreates itself

The Trash and installers (.dmg, .pkg) of apps you already installed.
App caches (browsers, Slack, Spotify…), with the app closed.
Old logs in ~/Library/Logs.
If you program: Xcode build data, and npm, pip, Homebrew or Gradle caches. They can add up to tens of GB.

Then, big things that need a decision

These can be recovered, but at a cost, so look before deleting: old iPhone backups (keep the latest one), iPhone simulators, Docker images and volumes, AI models you no longer use, and apps you haven't opened in months.

Last: your own files (better move them)

Forgotten downloads, duplicates, old videos. Here it's better to move than delete: an external drive, iCloud, or at least the Trash for a while, in case you change your mind. Sort Downloads by size and by “Date Last Opened” to find the forgotten ones.

What never to delete

Anything inside /System or /Library you don't know (macOS protects most of it anyway).
Your Photos library as a whole: delete photos from inside Photos, never the library file.
Folders in Application Support of apps you still use: that's where their data lives.
Anything a “cleaner” marks without telling you what it is.

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Folders in this guide

Trash~/.TrashReview
Installers in Downloads~/Downloads/*.dmg, *.pkg, *.zip, *.iso, *.xipReview
Chrome web cache~/Library/Caches/Google/ChromeRecreates itself
Homebrew cache~/Library/Caches/HomebrewRecreates itself
Xcode build data~/Library/Developer/Xcode/DerivedDataRecreates itself
iPhone backups~/Library/Application Support/MobileSync/BackupReview
Photos library~/Pictures/*.photoslibraryYour data
App logs~/Library/LogsRecreates itself