Breakdown: why your disk is full, in plain words
Breakdown starts from the numbers macOS reports, the same ones System Settings shows, and explains each part of the disk in a sentence. Whatever MacClearings can't see is shown as a number, with the usual reasons, not hidden.
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macOS 15+ · Apple silicon and Intel
- Starts where System Settings does
- The disk's APFS volumes come from diskutil and local snapshots from tmutil, so the total matches what macOS reports before anything is explained.
- Six parts, each in a sentence
- macOS, Apps, Your files, App data in your Library, Shared and system data, and what MacClearings can't see. Open a row to see what's inside it.
- Frees on its own, labeled
- Purgeable space, swap, local snapshots and macOS working files are explained as things macOS clears by itself. They are never offered as a cleanup.
- The remainder is a number
- In the screenshot, MacClearings accounts for 613 GB of 716 GB used. The other 103 GB is listed at the bottom with what usually makes it up.
- It only reads
- Breakdown runs diskutil, tmutil and xcrun simctl and measures folders. Nothing on the page stages or moves anything.
Why the storage bar needs explaining
System Settings shows your disk as a colored bar with a few categories. Much of the space often lands in one gray block called System Data, with no way to see what's inside. The diagram below shows the idea with example numbers.
Macintosh HD · 401 GB of 500 GB used
Example numbers- Applications64 GB
- Documents118 GB
- Developer52 GB
- Photos41 GB
- macOS22 GB
- System Data104 GB
What’s usually inside System Data
- Caches
- App, browser and system caches. Most refill on their own.
- Local snapshots
- Time Machine keeps these on the disk until it needs the space.
- Virtual memory
- Swap files and the sleep image, managed by macOS.
- App data
- Containers and support files in your Library.
- Logs
- Diagnostic and crash reports.
- Purgeable
- Space macOS can free by itself when an app needs it.
Breakdown keeps the starting point the same, so the numbers match what macOS reports, and then explains every part it can measure. The guide to clearing System Data covers what macOS lets you do about each piece by hand.
How Breakdown measures
Breakdown reads how the disk is divided with diskutil (the APFS volumes macOS keeps apart from your files) and tmutil listlocalsnapshots (local Time Machine snapshots). It lists simulator runtimes with xcrun simctl runtime list. Then it measures folders, using your latest scan where it covers them and a fresh read-only scan where it doesn't. It runs when you open the page, and Measure Again runs it once more.
The summary at the top says how much of the used space is purgeable. In the screenshot: "49.5 GB of it is purgeable: macOS frees it on its own when space runs low, so System Settings counts it as available." The guide to purgeable space on a Mac explains why it doesn't go on command.
The six parts
| Part | What's in it |
|---|---|
| macOS | The signed, read-only copy of macOS, startup and recovery, and swap and the sleep image |
| Apps | The Applications folder. Each app's caches and data are counted with your Library |
| Your files | Desktop, Documents, Downloads, Pictures, Movies, Music, the Trash, and other folders outside Library, including hidden ones developer tools keep, like .npm or .cargo |
| App data in your Library | Caches, app containers, Application Support, device backups, Xcode data, iCloud Drive and other cloud storage folders, Mail, Messages and logs |
| Shared and system data | Data installed for every user, downloaded macOS assets, macOS working files, command-line tools, other users and simulator runtimes |
| Can't see | The remainder, explained at the bottom of the page |
Each row has a size, a sentence about what it is and, where it has parts, a chevron that opens them. Hover over a row and a button appears that reveals it in Finder.
Labels on the rows
- Frees on its own marks things macOS clears by itself, like swap files and macOS working files. There's nothing to clean up.
- See suggestions marks things Suggestions covers. It opens Suggestions.
- Needs Full Disk Access marks folders macOS hides until you allow access. Clicking it opens System Settings.
- Partly hidden by macOS means only macOS can read some of it, so the size may be smaller than it really is.
- Managed by its own app marks data like Docker Desktop's disk image, which its own app keeps track of. MacClearings only shows it.
Where apps keep clones of themselves, a note says how much cloned space isn't counted twice.
What MacClearings can't see
The last card lists what usually makes up the difference between the used space and what the folders add up to:
- Local snapshots, with how many there are and when the oldest was made. Time Machine and macOS updates keep them so recent changes can be undone, and macOS frees them after about a day, or sooner when space runs low. The guide to Time Machine local snapshots covers them.
- The Spotlight index, document version history and other files only macOS can read.
- Folders macOS hides without Full Disk Access.
- Files that changed since your last scan.
The guide Mac storage not adding up goes through the same causes from the macOS side.
What Breakdown doesn't do
Breakdown never stages or moves anything, and it covers the startup disk only. To act on what it shows, use Suggestions for the parts it labels, or the Map to pick folders yourself. For data another app manages, it shows where to manage it instead, such as Xcode's settings for simulator runtimes or Finder for device backups. The field guide has the same plain-language entries for about 220 folders.
Guides
- System Data on a Mac: what it is and how to clear it safelyWhat System Data on a Mac holds, why it grows, and how to shrink it safely on macOS 15, 26 and 27, with Settings, Finder and Terminal, and what to leave alone.
- Purgeable space on a Mac: what it is and how to clear itPurgeable space is storage macOS can free on its own. What's in it, how to see it, why it doesn't always purge, and how to clear it safely in Terminal.
- Mac storage full for no reason? Why the numbers don't add upWhy Mac storage looks full for no reason, and why Finder, System Settings, Disk Utility and Terminal disagree: purgeable space, snapshots, clones and more.
- Time Machine local snapshots: what they are and how to delete themWhat Time Machine local snapshots are, where they're stored, how much space they use, and how to delete them safely in Time Machine settings or with tmutil.
Questions about Breakdown
What is System Data on a Mac?
System Data is the part of the storage bar in System Settings that doesn't fit Apple's other categories. It usually holds app caches and data in your Library, local Time Machine snapshots, swap files, logs and files macOS downloads for its own features. Breakdown splits it into named parts with a sentence about each.
Can Breakdown clear System Data?
No. Breakdown only reads. Parts that are safe to move, like Xcode build data or old logs, carry a See suggestions label that opens Suggestions, where you review them before anything moves to the Trash. Parts macOS frees on its own, like local snapshots and swap, are labeled Frees on its own and are never offered as a cleanup.
Why don't the parts add up exactly to the used space?
Some space can't be measured folder by folder: local snapshots, the Spotlight index, document version history, folders macOS hides without Full Disk Access, and files changed since your last scan. Breakdown reports that difference as one number with those reasons. When cloned files make the folders add up to more than the disk holds, it says that too.
Does Breakdown need Full Disk Access?
It works without it. Folders macOS hides, like Mail, Messages and Safari data, are marked Needs Full Disk Access and their space is counted in the remainder instead of being guessed. Clicking the label opens the right pane in System Settings.
Find out what's filling your Mac.
MacClearings explains your disk in plain words and moves only what you review to the Trash, with Undo. Paid once, every update included.
$12.50 launch price for the first 25 buyers, then $25.
macOS 15+ · Apple silicon and Intel