This paper discusses a user interface design tool for use in the Alvey ECLIPSE project. ECLIPSE is a second-generation integrated project support environment for medium to large software projects. Currently tool user interfaces in ECLIPSE are written in the Format Description Language (FDL) which defines the objects the user sees on the screen and how he/she interacts with them. FDL is interpreted at run time by a user interface management system. However, a language-based approach makes it difficult to visualise the user interface. A more direct approach is required (especially for the graphical interfaces used in Eclipse) to assist rapid prototyping and permit more user involvement in design. This paper looks at a tool for the "Direct Manipulation" [1] of interface objects and the methodology surrounding the tool. The tool is the centre of a design-prototype-evaluate iterative loop.