With well over 400 app extensions and plugins managed by PlugInKit in Sequoia 15.4.1, this article tries to give an overview of their management and control, as well as the diversity of their functions. This follows:

• a general introduction
• an account of discovery and management by PlugInKit
• AppexIndexer to examine appexes known to PlugInKit
• Apple’s appex Home page for developers.

Appex types

Although Apple refers to the type identifier for appexes as NSExtensionPointIdentifier in its developer documentation, where it lists some of them, in macOS this is also synonymous with NSExtensionPointName. In pluginkit dumps, it’s referred to as the SDK, and LaunchServices dumps use both terms, NSExtensionPointName in NSExtensionsAttributes, and NSExtensionPointIdentifier in NSExtension. This is even more confused in the log, where PlugInKit’s entries use the term NSExtensionPointName, but use NSExtensionIdentifier to refer instead to the appex-specific identifier, such as com.apple.iCal.CalendarWidgetExtension.

For the sake of clarity and consistency here, I’ll refer to the appex type identifier as NSExtensionPointName.

Appex locations

Many appexes supplied in macOS are stored as bundles inside dedicated collections such as /System/Library/ExtensionKit/Extensions or in frameworks. Where they are supplied in an app or similar bundle, they’re normally in a PlugIns folder, although according to this article QuickLook generators should be installed in Library/QuickLook, and Spotlight importers in Library/Spotlight.

Types and management

The rest of this article lists appex types, omitting the universal prefix com.apple., according to their management and discovery by PlugInKit during startup. I provide for each, as far as I’m able to tell, the type-specific manager, any controls provided in System Settings or elsewhere, and illustrative examples and other relevant information.

Type-specific managers are those services or subsystems that PlugInKit hands over to during discovery. For example, when it discovers appexes that extend QuickLook by providing either thumbnails or previews, PlugInKit hands those over to com.apple.quicklook.ThumbnailsAgent to manage.

Many appex types aren’t exposed in System Settings, are managed by PlugInKit, but don’t appear to undergo startup discovery. I have relegated those to the appendix at the end. Most of those are single-appex types, and others are only used by macOS.

Appex types that are managed in System Settings and by PlugInKit, and undergo startup discovery:

• FinderSync, managed by the Finder, and controlled in File Providers settings, e.g. Keka Finder Integration
• quicklook.preview, managed by com.apple.quicklook.ThumbnailsAgent, and controlled in Quick Look settings; these are modern substitutes for qlgenerators
• quicklook.thumbnail, managed by com.apple.quicklook.ThumbnailsAgent, and controlled in Quick Look settings; these are modern substitutes for qlgenerators
• ui-services, managed by the Finder, and controlled in Actions settings, includes Markup, ShareSheetUI (not exposed in settings)

Appex types that aren’t managed in System Settings, but are managed by PlugInKit, and undergo startup discovery:

• AppSSO.idp-extension, managed by AppSSOAgent, includes Kerberos and Sign In With Apple; these are single-sign-on extensions
• appstored-services.testflight, managed by appstoreagent; these handle App Store TestFlight
• AudioUnit, managed by AudioComponentRegistrar and axassetsd, for WardaSynthesizer
• AudioUnit-Speech, managed by AudioComponentRegistrar and axassetsd, include KonaSynthesizer and AUSPs
• AudioUnit-UI, managed by AudioComponentRegistrar
• cache_delete_extension, managed by deleted; these support app-specific cache management
• contacts.donation, managed by contactsdonationagent; these exchange info with Contacts
• ctk-tokens, managed by ctkd, include CryptoTokenKit and PlatformSSOToken; these handle tokens for CryptoTokenKit
• diagnosticextensions-service, managed by ControlCenter and diagnosticextensionsd, includes many service-specific Diagnostic Extensions
• email.extension, managed by maild, e.g. SpamSieve; these are Mail plugins
• fileprovider-nonui, managed by the Finder, includes iCloud Drive and PhotosFileProvider
• services, managed by the Finder; none listed
• spotlight.import, managed by mdbulkimport, includes PDFImporter
• spotlight.index, managed by corespotlightd, includes system extensions but not mdimporters
• textinputmethod-services, managed by imklaunchagent, includes many Input Methods
• usernotifications.content-extension, managed by NotificationCenter, includes ContentExtensions
• widgetkit-extension, managed by chronod, includes system and third-party widgets.

Significant appex types that are managed by PlugInKit, but don’t undergo startup discovery:

• appintents-extension, multiple instances
• intents-service, many IntentsExtensions
• photo-editing, Photos editing, controlled in Photos Editing settings
• Safari.extension, Safari extensions, managed in Safari settings
• share-services, many Share extensions, managed in Sharing settings
• widget-extension, only a couple, e.g. iStat Menus.

Appex types that apparently aren’t managed by PlugInKit, but are controlled in System Settings:

• Dock Tiles
• Finder, these are services offered in the Finder’s Services menu
• Spotlight, these are mdimporters.

also Safari.content-blocker, which is managed in Safari settings rather than System Settings.

Appex types that aren’t apparently managed by PlugInKit or controlled in System Settings:

• authentication-services-account-authentication-modification-ui
• authentication-services-credential-provider-ui
• broadcast-services-setupui
• broadcast-services-upload
• callkit.call-directory
• classkit.context-provider
• dt.Xcode.extension.source-editor
• fileprovider-actionsui
• identitylookup.classification-ui
• identitylookup.message-filter
• intents-ui-service
• keyboard-service
• networkextension.app-proxy
• photo-project
• tv-top-shelf

Appendix:

Appex types that aren’t exposed in System Settings, are managed by PlugInKit, but don’t undergo startup discovery

System, multiple appexes:
followup-extension – multiple FollowUpExtensions
lighthouse.SAOrchestratedExtension – multiple Ingestors
message-payload-provider – multiple
mlhost.worker – many ML-related
mlruntime.extension-point-high
mlruntime.extension-point-ondemand
mlruntime.extension-point-restricted
screensaver – several ScreenSavers
Settings.extension.ui – System Settings
storagemanagement – many apps
usernotifications.service – several NotificationServiceExtensions
wallpaper – several Wallpapers

System, single-app extensions:
amsengagementd-extension – Books, News
amsutility-extension – News
app.non-ui-extension – Swift Playground
app.non-ui-extension.multiple-instances – Swift Playground
app.ui-extension.multiple-instances – Swift Playground
applemediaservices.extensions.compose-review – ComposeReviewExtension
askpermission-extension – App Store related
askto.extension – AskToMessagesHost
calendar.EventKitUIRemoteUIService – EventKitUIRemoteUIExtension
calendar.virtualconference – FaceTimeExtension
contact-view – System Service
contacts.avatar-picker-ui – AvatarPickers
deviceactivity.monitor-extension – ScreenTimeDeviceActivityMonitorExtension
deviceactivityui.report-service – DeviceActivityReportService
extension-view-service-sample-rk – RPVideoEditorExtension_macOS, ReplayKit
extensionkit.app-extension-management – AppExtensionManagement
extensionkit.app-extension-settings – ExtensionKit components
facetime.notification – FaceTimeNotificationExtension
feedback.drafting-extension – Feedback
freeform.USD-renderer-remote-UI – USDRendererExtension
fskit.fsmodule – exfat and msdos file systems (File System Extensions)
GenerativePlaygroundUI.remoteUI – Image Playground
groupactivities – FaceTime RemotePeoplePicker
Home.ui-extension.userList – HomeUIUserList
ImagePlayground.NonUIExtension – GPNonUIExtension
ManagedSettings.service – ManagedClientMSExtension
mapkit.private.RemoteUI – MKRemoteUI for MapKit
mobileslideshow.photo-picker – PhotoPicker and PhotosPicker
networkextension.packet-tunnel – network extensions
PaperKit.extension.ui – PaperKitExtension
PassKit.in-app-payment-ui – Wallet
pdfkit-private – PDFExtensionView in PDFKit
people-picker – System Service
people.legacy.extension – PeopleLegacyMessageService
Photos.MacMusicPickerExtension – PhotosMacMusicPickerExtension
preference.security.privacy – Apple Advertising
preference.sharing.service – Media Sharing
private.translation-api-support – TranslationAPISupportExtension
private.translation-ui – Translate
private.voiceshortcuts-ui – three extensions
replaykit.broadcast-picker – RPBroadcastActivityExtension_macOS in ReplayKit
screentime.web-service – ScreenTimeWebExtension.