This document discusses, among other things, a method of testing an Application Programming Interface (API) call that includes receiving data identifying a schema associated with web services together with an API call. Various example embodiments may relate to accessing a data repository associated with the schema to identify an API response corresponding to the API call. In some example embodiments, a message is returned that is based on a determination of whether the API call is valid. The example message may simulate an API response from web services.