Within the last years, ambitions towards the definition of common interfaces and the development of open frameworks have increased the efficiency of research on WCET analysis. The Annotation Language Challenge for WCET analysis has been proposed in line with these ambitions in order to push the development of common interfaces also to the level of annotation languages, which are crucial for the power of WCET analysis tools. In this paper we present a list of essential ingredients for a common WCET annotation language. The selected ingredients comprise a number of features available in different WCET analysis tools and add several new concepts we consider important. The annotation concepts are described in an format that can be instantiated at different representation levels.