The present work is an attempt to develop an Arabic expert system shell for general diagnosing systems. The system abbreviated as GADESS (General Arabic Diagnosing Expert System Shell), it is constructed of two phases. The first phase responsible for acquiring human expert knowledge in an automatic way provided with menu and windows message (expert interface). The acquired knowledge is analyzed by Arabic morphological system, which analyze the given Arabic phrase and find the required keywords (roots), the system also provided with the required domain dictionary. The second phase is concerned with the design of inference engine together with user interface that uses a backward chaining method (end-user interface). GADESS considers reasoning under uncertainty using certainty factor method (Stanford Certainty Factor). Also GADESS uses the external database approach to store the human expert knowledge in order to be used by the inference engine. GADESS supports two types of explanations "Why" and "How". The "Why" concerned the reason that the system asks a specific question, while the "How" concerned conclusion steps. GADESS was implemented using Visual Prolog version 5.0 with its supplement tools for building the inference engine and for building the interface tools.