Tidy MacSystem Data grows because several parts of macOS and your apps add to it on purpose: Time Machine makes hourly local snapshots, apps grow their caches, Finder adds device backups, developer tools and AI apps download large files, and occasionally a system cache runs away. Find what grew this week, fix that one thing, and set an alert so it can’t surprise you again.
- Note your System Data size today in System Settings › General › Storage.
- Check the same number again in a few days to confirm it is really growing.
- Look at snapshots, ~/Library/Caches and ~/Library/Developer for what changed.
- Fix the one thing that grew instead of deleting caches across the board.
What adds to System Data over time
- Time Machine local snapshots, hourly, kept up to 24 hours (longer if your backup disk isn’t connected).
- App caches: browsers, Spotify, Slack, Teams and Xcode grow theirs until macOS needs the space.
- Device backups each time an iPhone or iPad syncs with Finder.
- Developer and AI files: Docker images, simulators, package caches, local AI models.
- Logs and diagnostic reports, usually small unless something is crashing repeatedly.
- Known runaway caches, such as com.apple.mediaanalysisd on some macOS versions.
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How to see what grew
Take two measurements a few days apart:
du -sh ~/Library/Caches ~/Library/Developer ~/Library/Application\ Support 2>/dev/nullTidy Mac notes free space every 15 minutes while it runs, shows the trend over 24 hours, 7 days and 30 days in its menu bar panel, and sends a notification when used space jumps.
Keep it in check
Fix the part that grows, not everything at once: clearing all caches only makes apps rebuild them. A monthly check, or an alert when free space gets low, is enough.