The gnatcheck tool is an ASIS-based utility that checks properties of Ada source files according to a given set of semantic rules. In order to check compliance with a given rule, gnatcheck has to semantically analyze the Ada sources. Therefore, checks can only be performed on legal Ada units. Moreover, when a unit depends semantically upon units located outside the current directory, the source search path has to be provided when calling gnatcheck, either through a specified project file or through gnatcheck switches.
For full details, refer to GNATcheck Reference Manual document.