These days, embedded systems such as robotics and car navigation systems are composed of a variety of software components. These systems frequently suffer environmental damage and require changes. Improving the adaptation cycles in the development phase is a big challenge in this area. We will provide an extensible online log analysis system that will reduce the debugging cost of the real-time system in the development phase. A real-time system is used as the base of the system. To achieve this, we offer two proposals: One is the online log analysis architecture that will not disturb the target observed system. The second is an extensible analysis framework for detecting errors and faults in the target real-time system. Our system provides methods for treating both input log streams and output results. Results will be shown in the Web browser viewer for root cause analysis by engineers. This system will help the incremental development of complex systems such as robotics that require adaptable improvements in either the developmental or operational phases. In this paper, we will show the prototype architecture and examine its results.