A method and apparatus to employ a service proxy to dynamically personalize Web service messages by automatically supplying the interface parameters used for communications between a Web service provider and its client businesses. The service proxy does this according to context parameters that the client businesses specifies during configuration set up at the Web service provider's Web site and in messages used to communicate with one or more Web services. For simpler administration, the context variables may be organized in multiple kinds of hierarchies by which communications parameters specified at a higher level are automatically applied to categories at a lower level, although parameters specified directly for a lower-level category will override parameters from a higher category.