Mac App Store apps can only look at folders you choose. Pick your Home folder to see what fills it, or choose a whole disk such as Macintosh HD or an external drive.

macOS protects some folders – other apps’ data, Contacts, Calendars, Mail, Messages, the Photos library – and would ask a separate permission for each. StorageSpace skips them instead. To measure them too, turn on Full Disk Access once: click Open Full Disk Access Settings in StorageSpace, drag StorageSpace from the Finder window into the list (or click + and choose it) and switch it on. StorageSpace rescans by itself.

That is normal: macOS lists an app there only after it has been added once. Click + below the list and choose StorageSpace in Applications, or drag it into the list from Finder.

It is everything outside your own files: local Time Machine snapshots, caches and logs, iPhone backups, virtual machines and space reserved by macOS. StorageSpace shows how big this part is and which of it can be found in your Home folder; the rest is managed by macOS.

StorageSpace moves files to the Trash, so you can undo. Empty the Trash in Finder to get the space back.

Your Home, Library and its main folders, the Photos library, iCloud Drive, Mail and system folders are protected, because removing them would do more harm than good. Open them and select what is inside instead.

Analyzing, the map and every list are free, and you can try one cleanup of up to 1 GB. StorageSpace Pro is a one-time purchase that unlocks Move to Trash without limits. No subscription.

Use the same Apple Account, open StorageSpace and choose Restore Purchases in the StorageSpace menu or in the Pro window.