An accessory device application executes on an accessory device of limited resources. The accessory device application includes an accessory device stub application and an interface definition. When a user interacts with the accessory device application, display changes are generated in response, in accordance with the interface definition, and are sent to a companion extension at an associated companion device. The companion extension receives the changes, and generates updated display values for the accessory device display. The updated display values are sent from the companion device daemon to the daemon of the accessory device, which displays the updated display values at the accessory device display. The functionality and operation of the accessory device application permit an accessory device of limited resources to leverage data processing and computational power of the companion device, to provide a more involving user experience at the accessory device.