Abstract: A stateful rules verification platform is described. The verification platform implements a specification language to provide a formal definition for rules used to test target systems having a central module that provides APIs (“API provider”) and applications (“API clients”) that use the APIs. Rules may be defined in terms of transitions on state elements associated with interactions between API providers and API clients. The rules defined in accordance with the specification language enable run-time verification in which calls may be intercepted and run-time code to implement checks may automatically be generated and injected to test behaviors of the intercepted calls. The same set of rules may also be employed for static verification during compilation. Additionally, the specification language includes constructs to provide rule descriptions and comments with rules definitions that facilitate publication of the rules and documentation of misbehavior identified during verification.