Live programming is a programming style in which the repetitive task of compiling and running the software being programmed is managed automatically. This style can be a helpful practice in End-User Development (EUD) where the non-professional end-users are to be supported through techniques and tools that empower them to create or modify software artifacts. Mashups — a form of lightweight Web applications composing reusable content and functionalities available on the Web — are a popular target for EUD activities on the Web. EUD for mashups is enabled by intuitive composition environments, called mashup tools. In this paper, we introduce live mashup tools, a new class of mashup tools based on the live programming style. We give a comprehensive definition and classification of live mashup tools, giving examples of how well existing tools fit in this category and discuss open research challenges and opportunities.