When creating applications that should be available on multiple computing platforms, designers have to cope with different design tools and user interface toolkits. Incompatibilities between these design tools and toolkits make it hard to keep multi-device user interfaces consistent. This paper presents Jelly, a flexible design environment that can target a broad set of computing devices and toolkits. Jelly enables designers to copy parts of a user interface from one device to another and to maintain the different user interfaces in concert using linked editing. Our approach lowers the burden of designing multi-device user interfaces by eliminating the need to switch between different design tools and by providing tool support for keeping the user interfaces consistent across different platforms and toolkits. Categories and Subject Descriptors H.5.2 [Information interfaces and presentation]: User Interfaces