What is this Xcode folder?
Found something big or strange in ~/Library/Developer or Activity Monitor? What each one is, why it's there, and whether you can delete it. Checked on a real Mac with Xcode 27.
Folders
CoreDevice/DeviceFS
DeviceFS is a virtual file system macOS mounts for running simulators. Tools like du count it as 100+ GB, but it uses no disk space. Don't delete it.
CoreSimulator/Volumes
Each folder in /Library/Developer/CoreSimulator/Volumes is a mounted iOS simulator runtime. Folder tools over-count them; xcrun simctl shows the real size and deletes them safely.
ModuleCache.noindex
ModuleCache.noindex is Xcode's shared cache of compiled Swift and Clang modules, used by every project. Safe to delete; every project rebuilds its modules once.
SDKExplicitPrecompiledModules
SDKExplicitPrecompiledModules holds precompiled SDK modules (.pcm files) that Xcode reuses across projects. A cache: safe to delete, rebuilt as needed.
CompilationCache.noindex
CompilationCache.noindex is where Xcode keeps compilation cache results when the Enable Compilation Caching build setting is on. Safe to delete.
SymbolCache.noindex
SymbolCache.noindex is a small cache Xcode creates in DerivedData, with a folder per SDK version. Safe to delete with Xcode closed.
SDKStatCaches.noindex
SDKStatCaches.noindex holds one small .sdkstatcache file per SDK version that Xcode uses during builds. A few MB; safe to delete.
Index.noindex
Index.noindex inside each project's DerivedData folder is Xcode's code index, behind autocomplete, jump to definition and search. Safe to delete; Xcode re-indexes.
XCTestDevices
XCTestDevices holds the simulator clones Xcode creates to run tests in parallel. It can grow after test runs; safe to empty with Xcode and tests stopped.
Xcode Previews data
UserData/Previews holds the simulator devices SwiftUI Previews run in. It can grow with heavy Previews use; safe to clear with Xcode closed.
CoreSimulator logs
~/Library/Logs/CoreSimulator holds log folders for each simulator, named by its UDID. Usually tens of MB; safe to delete.
Processes
simdiskimaged
simdiskimaged is the macOS service behind iOS simulator runtime disk images. It runs while simulators are in use; don't force quit it.
CoreSimulatorService
CoreSimulatorService runs and manages iOS simulators for Xcode and xcrun simctl. Normal while you use simulators; quitting Simulator usually calms it.
SourceKitService
SourceKitService is Xcode's Swift language service behind code completion, syntax highlighting and indexing. Why it gets busy, and the usual fixes.
Looking for step-by-step cleanups? See the guides.