"Developer" in Mac storage: what macOS counts, and the larger half it leaves out

Open System Settings, General, Storage and there may be a line called Developer with a large number next to it. It looks like the answer to where your developer space went. It is roughly half of it.

What the Developer category counts

It counts what Apple's own tools put in ~/Library/Developer: Xcode's DerivedData, archives, device support for each iOS version, and simulator data. Click the info button and macOS lists some of these, with an option to remove some of them. It may not let you remove all of them from there.

du -sh ~/Library/Developer/* 2>/dev/null | sort -h

What it leaves out

So a web or backend developer can see a Developer total of a few gigabytes while their real tooling uses many times more, spread over three other categories. That is the main reason System Data looks so large on developer Macs.

Seeing the whole picture from Terminal

du -sh ~/.npm ~/.cargo ~/.gradle ~/.m2 ~/go ~/Library/Caches/pip \
  ~/Library/Developer ~/Library/Containers/com.docker.docker 2>/dev/null | sort -h

# node_modules across your code folder
find ~/code -name node_modules -type d -prune -exec du -sh {} + 2>/dev/null | sort -h | tail

Change ~/code to wherever your projects live. Our developer cleanup script wraps the safe clean commands for each tool, and the developer storage tools comparison shows which apps see these folders.