Nowadays, Mixed- and Virtual Reality devices suffer from a too small field of view with respect to human visual perception. Although, a larger field of view is useful (e.g., conveying peripheral information or improving situation awareness) technical limitations do not allow to easily extend the field-of-view. A way to overcome these limitations is to extend the field-of-view with peripheral light displays. However, there are no tools to support the design of peripheral light displays for Mixed- or Virtual Reality devices. Therefore, we present our prototyping tool PeriMR that allows to develop new peripheral head-mounted light displays for Mixed- and Virtual Reality.