A server system provided according to an aspect of the present disclosure receives validation rules for fields of a form, and stores the validation rules as metadata in a memory. When values are later received based on the form, the values are validated using the rules in the metadata. Any errors detected are notified to a user system from which the values are received. The values are forwarded to a corresponding application if no errors are detected. According to another aspect, a developer of the application provides an initial set of validation rules prior to the application being deployed at a customer site. The customer then specifies additional rules. The metadata stores both the initial rules and the additional rules. A user interface module validates each received value against any applicable rules present in the metadata.