When done right, sound design can greatly enhance both physical and digital products. The sounds used to underscore interactions with products are typically short, with an emphasis on timbre and shape, focusing on character rather than musical features, which requires particular approaches to sound sculpting. However, designers often lack the needed tools and skills, including the language to describe sound features, to integrate sound design in their process, particularly in early stage design activities. This study presents and discusses a set of requirements for sonic sketching tools specifically tailored to UX (User Experience) designers. The requirements were distilled by means of generative design research methods, including interviews with UX experts, context mapping, prototyping activities and user testing. Currently, Timbreworld, a workbench prototype for sonic sketching in UX is being built, tested and iterated, and early results are outlined.