'Other' System Data Explained: The Developer's Guide

The "System Data" (formerly "Other") storage category is the most searched macOS problem on Google.

Why? Because Apple provides zero transparency. You see a grey bar consuming 150GB, and macOS just shrugs.

As a developer, "System Data" is usually not mysterious. It is just files in ~/Library that don't look like Documents or Photos.

Here is exactly what makes up that 150GB.

1. The Cache Monster (~/Library/Caches)

Apps cache content to load faster. Browsers, Spotify, Xcode, Slack—they all dump files here.

• Spotify: Can easily be 10GB.
• Chrome/Brave: Often 5-10GB of cached images and scripts.
• Yarn/NPM: Package caches.

Verdict: safe to delete. Apps will regenerate what they need.

2. The Log Hoard (~/Library/Logs)

If you have crashed apps, failed builds, or verbose debug tools running, your logs can spiral out of control.

We have seen CoreSimulator logs take up 40GB after a few months of intense iOS testing.

Verdict: Delete everything. You likely do not need logs from 2023.

3. Application Support (~/Library/Application Support)

This is the dangerous one. This isn't just cache; it's persistent state.

• Simulators: iOS device images lives here (in CoreSimulator).
• Docker: VM disks live here (in Containers).
• Mail: Your local email database.

Verdict: DO NOT delete blindly. You will lose data (like email history or save games). Always backup your Mac before deleting files in this folder.

The "Orphan" Problem

The real bloat comes from apps you already deleted.

When you drag an app to the Trash, its Application Support folder often stays behind. If you deleted "Adobe Creative Cloud" a year ago, you might still have 8GB of cache files sitting in System Data.

How to Investigate

You _could_ roam around ~/Library with Finder (Cmd+Shift+G), checking Folder Info (Cmd+I) on every directory.

Or you can map it.

A future Mac version is planned to visualize ~/Library. It is not available yet. The app you can buy today runs on Windows.

Until that Mac version ships, use Finder (Cmd+Shift+G) and check folder sizes yourself. Do not follow a "Scan Home Folder" step in Scan My Disk on a Mac. That button is not available. Checking those folder sizes in Finder is how you reclaim "System Data" until the Mac app ships.

Map Your System Data with Scan My Disk →