Techniques for configuring validation rules in a client-server architecture, and for enforcing such validation rules are provided. A developer is enabled to configure a display screen for an application to enable a user at a client to input data. The developer is further enabled to input a validation rule that is configured to be applied to validate the data at the client and/or at a server. The validation rule is integrated into code of the application. During execution of the application, a client-side rules engine may be present to evaluate the validation rule at the client, and a server-side rules engine may be present to evaluate the validation rule at the server. The client-side rules engine and server-side rules engine may be configured to evaluate validation rules in an asynchronous manner.