An augmented reality or virtual reality (AR/VR) device pairs with a companion device to augment input interfaces associated with an AR/VR application at the AR/VR device. In implementations, an AR/VR device determines a portion of a markup file that corresponds to an AR/VR scene of a plurality of AR/VR scenes in an AR/VR environment, and communicates the portion of the markup file to the companion device to cause the companion device to configure a companion user interface associated with initiating an action as part of the AR/VR scene. In response to receiving user input via the companion user interface, the companion device communicates the action to the AR/VR device to initiate the action. The AR/VR device receives input data from the companion device, and initiates the action for the AR/VR scene.