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Why is CoreSimulator taking up so much space on my Mac?

~/Library/Developer/CoreSimulator/Devices
/System/Library/AssetsV2/com_apple_MobileAsset_iOSSimulatorRuntime
/Library/Developer/CoreSimulator/Volumes

By Parsa Nasirimehr

Two things live under CoreSimulator: the simulators you created, each with its own apps and data, and the OS runtimes they boot, several gigabytes per iOS version. Simulators for runtimes you removed stay behind. Both can be cleared with Xcode's own tools.

How big it gets

On the Mac we measured, a working developer's Mac on macOS 27: Devices: 23.8 GB in 47 simulators, 29 of them for runtimes no longer installed. Runtimes: 35.1 GB on disk for iOS 18.6, 27.0, 27.1, watchOS 27 and the 8.5 GB parent image of iOS 18.6, which simctl's total leaves out (see simulator runtimes).

What it is

What writes itXcode and the Simulator app. Each new Xcode version adds simulators for its devices, and each downloaded runtime adds an image.
Devices~/Library/Developer/CoreSimulator/Devices/<UDID>: one folder per simulator, holding its installed apps, their data and its settings. The largest here held 8.0 GB.
RuntimesCompressed disk images, usually 3.5 to 8.5 GB each, in /System/Library/AssetsV2 or /Library/Developer/CoreSimulator/Cryptex. They are mounted under /Library/Developer/CoreSimulator/Volumes.
Measure it rightDon't run du on Volumes: it counts the mounted, uncompressed contents (43.2 GB here instead of 35.1). xcrun simctl runtime list -v shows each runtime's real size.
Comes back?Simulators come back only if you create them; Xcode recreates its defaults. Runtimes come back only if you download that version again.

How to clear it

  1. Remove simulators whose runtime is gone: xcrun simctl delete unavailable
  2. Empty the rest without deleting them: xcrun simctl erase all (quit Simulator first).
  3. Remove runtimes you don't test on in Xcode › Settings › Components, or with xcrun simctl runtime delete <id> using an ID from xcrun simctl runtime list.

What you lose: Apps and data installed in those simulators, and the ability to test on removed OS versions until you download them again.

With Scrubs: Scrubs's Quick Wins lists simulator devices to move to the Trash, and simulator runtimes with a link to Xcode's Components settings, where Apple wants them removed. Download Scrubs; scanning is free.

Related folders

Simulator runtimesHow do you delete old iOS simulator runtimes on a Mac?DerivedDataWhat is DerivedData on a Mac, and can you delete it?iOS DeviceSupportWhat is iOS DeviceSupport on a Mac, and is it safe to delete?

Sizes measured with du on 1 November 2026. Paths and commands apply to macOS 15 and later. See also how to free up disk space on a Mac.

About the author: Parsa Nasirimehr is a mobile app developer who builds Scrubs, a disk map for the Mac. Spotted something wrong? Write to support@getscrubs.app.