WatchKit

WatchKit is Apple's framework for building apps and experiences for Apple Watch. Introduced with watchOS 1 in 2014 alongside iOS 8, it provides the APIs and user interface elements required to create watchOS applications that run on the Apple Watch and, in many cases, synchronize with a companion iPhone app.

An app using WatchKit comprises a WatchKit App bundle, which contains the watch-side user interface, and a WatchKit Extension that runs the app’s logic. In early releases the extension executed on the paired iPhone and communicated with a UI on the watch; starting with watchOS 2, watch applications could run code on the watch itself, enabling more independent, low-latency experiences while still using the iPhone for data synchronization when needed.

Developers design the watch UI with WKInterfaceController and a suite of interface objects such as WKInterfaceLabel, WKInterfaceButton, WKInterfaceTable, and WKInterfaceImage. The interface is defined in a storyboard, and navigation is handled by interface controllers. WatchKit provides support for notifications, complications, and data sharing through WatchConnectivity and related frameworks, with Swift or Objective-C as programming languages. Apps are built in Xcode and distributed via the App Store; users install the watch app as part of a paired iPhone app or directly on supported watchOS versions.

From watchOS 3 onward, Apple refined performance and user experience, and modern watchOS development also incorporates SwiftUI for creating watch interfaces, while WatchKit remains a maintained API surface for traditional, imperative watch interfaces. The framework continues to support health and fitness features, communications, and short interactions tailored for the Apple Watch.