Embodiments of the present invention address deficiencies of the art in respect to defect classification for software development and provide a method, system and computer program product for automated defect classification in a software development tool. In an embodiment of the invention, a defect classification method can be provided. The method can include computing differences between versions of a line of source code, lexically analyzing the computed differences to produce a lexical construct, mapping the lexical construct to a classification, and assigning the defect classification to the line of source code.