Because of the increased variety of operating systems and architectures, developing applications that are supported by multiple platforms has become a cumbersome task. To mitigate this problem, many portable APIs were created which are responsible for hiding the details of the underlying layers of the system and they provide a universal interface on top of which applications can be built. Many times it is necessary to examine the interactions between an application and an API, either to check that the behavior of these interactions is the expected one or to confirm that this behavior is the same across platforms. In this thesis, the POSIX Omni Tracer tool is described. POSIX Omni Tracer provides an easy way to analyze the behavior of the POSIX API under various platforms. The behavior of the POSIX API can be captured in traces during an application’s execution using various tracing utilities. These traces are then parsed into a uniform representation. Since the captured behavior from different platforms share the same format, they can be easily analyzed or compared between them.