A method and system for tracing the failing or successful execution of nested functions coded with return codes in a thread during its execution. The method comprises an ENTRY and EXIT trace macro to mark the beginning and the end of execution of the function, a TRACE macro to record messages and program variable values, and a QUIT macro marking the failing execution of the corresponding function. Using a Graphical User Interface, an interactive trace analyzer reads the trace file and displays the tree structure of the nested functions and marks, by using different colors, the success or failure of each of them. The trace analyzer utilities help the user to quickly identify the error in the source code corresponding to a function with a failing execution.