iOS Simulator runtimes and devices — the 20 GB Xcode doesn't show you

Last updated: October 2026

Safe to delete — with the right tool

A runtime is a download: delete it and Xcode fetches it again, 8 GB at a time. A device is a folder of simulated apps and their data: delete it and Xcode makes a fresh one, but the logins, databases and test fixtures inside the old one are gone.

Both are managed by a registry that rm does not know about, and current runtimes live where rm is not even allowed. Use simctl, and the one Xcode settings pane that actually shows the sizes.

Shodhana's Development page, iOS simulators section totalling 33.36 GB: an iOS 26.5 runtime at 7.9 GB and an iOS 18.6 runtime at 6.6 GB, each with a Delete button and a note of how many simulators use it; nine devices listed with their runtime and size, two of them — iPhone 15 Pro and iPhone 15 — marked 'runtime removed' in orange with Remove buttons; and a final row, 'Simulators whose runtime is gone', 4.31 GB, with Delete. — Runtimes first, with how many devices depend on each. Then every device, with its runtime and size. Only the two whose runtime is gone get a button up front — they can never boot again — and the last row removes all of them at once. Every button runs `simctl`.

Where they actually live now

The layout changed in Xcode 14, and most advice online predates it. On the Mac this guide was written on, with Xcode 27 and one iOS runtime installed:

/System/Library/AssetsV2/com_apple_MobileAsset_iOSSimulatorRuntime/
  …/AssetData/Restore/094-56039-099.dmg      7.9 GB — the runtime itself

/Library/Developer/CoreSimulator/Volumes/iOS_23F77/   where that image is mounted

~/Library/Developer/CoreSimulator/Devices/     15 GB — one folder per device
  31B3D85A-…/data/                             apps, Documents, Library, tmp

A runtime is a signed disk image, delivered through the same mechanism as system software updates, stored under /System/Library/AssetsV2 — a path System Integrity Protection keeps you out of — and mounted on demand under /Library/Developer/CoreSimulator/Volumes. Older Xcodes kept runtimes as .simruntime bundles under /Library/Developer/CoreSimulator/Profiles/Runtimes; if that folder still has contents on your Mac, they are from an Xcode you no longer run.

Devices are the other half, and often the larger one. Every simulated iPhone keeps the apps installed on it, their data, caches and logs, in a folder named by its UDID. Fifteen gigabytes here, across devices Xcode created on its own, one per model it offers, most never booted by a person.

See what you have

Runtimes, with state, size and the last time each was used:

xcrun simctl runtime list -v

Devices, grouped by runtime. The ones marked unavailable belong to a runtime that is no longer installed — pure waste:

xcrun simctl list devices

And which device folders hold the space, biggest last; the UDID in the path matches the one in parentheses in the list above:

du -sh ~/Library/Developer/CoreSimulator/Devices/*/ | sort -h | tail

Xcode has one view of this too: Xcode › Settings › Components, under Other Installed Platforms, lists every runtime with the storage you recover by deleting it. Nothing in Xcode shows the devices.

Delete runtimes you no longer target

Keep the runtime your app ships against and the one before it. Delete the rest by the identifier from the listing — the UUID, or the build number such as 23F77, both work:

xcrun simctl runtime delete 23F77

Or the information button next to the runtime in the Components pane, then Delete. Both go through the same registry. A runtime deletes in seconds and downloads again in minutes, so there is little to agonise over; the only real cost is the download.

Delete devices

First the free win — every device whose runtime is gone, in one command, no data worth keeping in any of them:

xcrun simctl delete unavailable

Then individual devices you do not use, by UDID:

xcrun simctl delete 31B3D85A-1F84-4A64-A36F-FD03D39B5D23

If you want the devices but not what is in them — a clean slate rather than fewer slates — erase instead of delete. Every device returns to its just-created state, apps and data gone, device kept:

xcrun simctl erase all

Quit the Simulator app before any of these. A booted device is in use, and simctl will say so.

Do not delete: the folders behind the registry

Do not touch

/Library/Developer/CoreSimulator/Volumes/ and ~/Library/Developer/CoreSimulator/Devices/<UDID>

Volumes are mount points for live disk images, not copies — there is nothing to free by deleting them, and plenty to confuse. The device folders are tracked in a registry beside them; remove one by hand and simctl still lists the device, Xcode still offers it as a run destination, and the first attempt to boot it fails. The asset store under /System/Library/AssetsV2 is protected by the system, and the one way people find to get past that leaves a runtime the registry cannot see and cannot delete. Every one of these has a simctl command; use it.

Why it comes back

Each Xcode update ships with a new runtime, and offers to download it on first launch; say yes every time and you have one per Xcode you ever installed. Each runtime gets a device per model Xcode knows, created automatically, and every build-and-run installs your app and its data into whichever device was selected. A year of this is a runtime a season and a few hundred megabytes a week in device data, none of it ever removed. A quarterly runtime delete of last season's runtime, followed by delete unavailable, is the whole maintenance routine.