This paper extends a notion of local grammars in formal language theory to autosegmental representations, in order to develop a sufficiently expressive yet computationally restrictive theory of well-formedness in natural language tone patterns. More specifically, it shows how to define a class ASL\ of stringsets using local grammars over autosegmental representations and a mapping g from strings to autosegmental structures. It then defines a particular class ASL\ using autosegmental representations specific to tone and compares its expressivity to established formal language (...) grammars that have been successfully applied to other areas of phonology. (shrink)