Interface design and ergonomics, while already studied in much of educational theory, have not until recently been considered in language testing (Fulcher, 2003). In this paper, we revise the design principles of PLEVALEX, a fully operational prototype Internet based language testing platform. Our focus here is to show PLEVALEX's interfaces and indicate their relation to Fulcher's design principles (2003). We also suggest some tentative design changes for further projects. Additionally, we will summarise how PLEVALEX benefits from the validity and reliability features of general tests delivered through computers. Traditionally, interfaces in language testing have not received special attention in language testing because designers of L2 platforms followed the same criteria for tests and general L2 learning platforms. In 2003, Fulcher was the first writer to formulate the basics of interface design to be taken into account in computer based language testing. Fulcher's theory is considered today as the main theoretical framework for Computer assisted language testing (CALT) interface design. This study evaluated the relation of the CALT PLEVALEX platform with his theories. Although the platform design has been justified by Garcia Laborda (2006a) and validated by Garcia Laborda (2006b), its design needs to be seen in light of the current theories of which Fulcher's is foremost. The key issue behind this study is to suggest the positive features that make of PLEVALEX a facilitating tool for delivering language testing. This paper is broadly divided into three sections: Introduction, Application of Fulcher's theoretical principles and conclusion. (Contains 2 figures and 1 table.) [This paper was originally published in "CALL EJ-Online" v9 n1 July 2007.]