The advantages of declarative end user task specification and those of automatic language tool generation are combined to produce individual user interface design environments that are maximally adapted to the specific requirements of the problem on hand. The development of the target design environment proceeds in two steps. First, a visual syntax-directed editor for a declarative task-oriented specification language is generated from formal specifications. The editor is then embedded with the functionalities required for the target design environment - the result is a customized user interface design environment. The initial results from experimenting with customized user interface design environments using our visual language specification framework and its editor generator are discussed.