Storage settings lumps a hundred-odd gigabytes into two gray bars, "macOS" and "System Data," and the little (i) button next to them explains nothing. SpacePig scans the whole disk, sorts it the way Settings does, and lets you click into every bar until you hit real files.
My Mac said 117 GB of System Data. So I spent an afternoon with du and diskutil and found 34 GB of cancelled Google Drive uploads, a 10 GB git repo full of video, and 20 GB of simulator runtimes I forgot I had. Then I wrote the app I wished I'd had at the start.
On my Mac, System Data and the big categories land within a couple of GB of what Settings shows. Apple doesn't publish how it sorts files, so SpacePig uses its own rules. They're a plain JSON file in the repo if you want to argue with one.
macOS splits into the sealed system volume, Preboot (Rosetta, the OS cryptex), Recovery, and the Siri and Apple Intelligence downloads. System Data splits into your Library, hidden folders, Homebrew, swap, and an "Unexplained" row for APFS overhead.
Size bars for reading. A treemap for spotting the one folder eating your disk.
Click a folder and it tells you what it is and whether to touch it. Spotlight index: leave it alone. Xcode DerivedData: go for it.
Caches, logs, simulator junk, old Homebrew versions, cancelled Drive uploads. Safe stuff starts checked and risky stuff doesn't. Nothing goes until you confirm.
A small helper runs as root so it can measure /private/var and other users' folders. Admins only, and it asks for your password before deleting anything system-wide.
Scanning never pulls down cloud-only files from iCloud Drive or Google Drive. It counts what's on the disk, nothing more.
Prefer building from source?
git clone https://github.com/xwrvnggp9n-star/SpacePig.git
cd SpacePig
scripts/build.sh --install # needs Xcode and XcodeGenSpacePig is free and MIT-licensed. If it found you 50 GB, buy me a coffee ☕