Glossary
Full Disk Access
A macOS privacy permission that lets an app read folders other apps and the system keep private.
What it is
macOS protects folders such as Mail, Messages, Safari data and other apps' containers. An app can only see inside them, or add up their sizes, after you turn on Full Disk Access for it in System Settings → Privacy & Security.
You grant it per app, and you can turn it off again at any time.
Why it matters
Without it, a disk analyzer undercounts the space your Library folder uses, and an uninstaller can miss an app's files.
In Activity Monitor
Not applicable. Activity Monitor doesn't read file sizes.
In iKnowMyMac
Asked the first time you open the Storage map, never at install. The rest of the app works without it.
Know why your Mac is slow.
macOS 15 Sequoia or later · Apple silicon. A 4.2 MB native app, notarized by Apple. No account, no analytics, no telemetry.
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