This paper introduces a component-based network management system for wireless sensor networks. The research is motivated by a variety of problems that occur due to the unpredictable behavior of wireless sensor networks. Once sensor nodes are deployed, the inner behavior of a sensor field can only be analyzed by monitoring incoming data packets at the sink node or base station, if only such a framework exists. In this paper, we present a component-based management system, RMTool, which allows developers to easily monitor and analyze the network status and interactively configure the network over unexpected problems while running applications over it. The system has been implemented on a multi-threaded sensor network operating system RETOS, which supports run-time loadable kernel modules. The preliminary evaluation shows that RMTool provides management functionalities as designed, and the implementation is efficient due to the component-based module architecture.