Methods and apparatus, including computer program products, for generation of customized client proxies. A method of generating client proxies includes receiving properties of a client, determining customizations for a client proxy based on the properties of the client, and generating the client proxy, where the client proxy includes the one or more customizations. Generating the client proxy can include generating the client proxy as executable code to execute on the client, source code to be compiled on the client, or a combination of source code and executable code. A customization can define a modification of a default client proxy, a combination of designtime objects for a client proxy, a combination of runtime objects for a client proxy, or a combination of all three techniques or different techniques.