Abstract: In a distributed system, a method and apparatus for automatically checking objects according to a specification which includes public contracts and private constraints. Public contracts are obeyed by both client and server, while private constraints are obeyed by either client or server, but for a given private constraint, not by both. At each and every stage of a client-to-server or server-to-client transaction or “call”, the objects or parameters related to call are automatically checked to ensure a specification is met. A client-side stub on the client automatically generates and executes checking code to check both private client-side constraints and public contracts on the client prior to network transfer to a server. The server has a server-side skeleton which intercepts the call and objects. The server-side skeleton performs checking by code automatically generated to check the public contracts, if any, with client and any private server-side constraints.