Monitoring dependability of city-scale IoT using D-case

City-scale IoT, a fundamental infrastructure for smart cities, requries to sense a range of ubiquitous entities in a city including humans, objects, and spaces. Ubiquitous sensor networks (USN) is the key technology to this. However, failures of a USN may result in hazards in our daily lives in smart cities. Monitoring of USN, rapid detection of faults and failures, and recovery from them are thus important for better applications of USN. This paper proposes a means to do so comprehensively by using Dependability Cases (D-Case). Since USN is a system composed of variety of components such ash wireless sensor nodes, database servers, and network appliances, we need a tool that can target them in common. Our tool enables to execute monitoring programs on a D-Case diagram, which is represented with Goal Structuing Notation (GSN), so that it can target a variety of devices and services.