Often tools need to be extended at runtime depending on the availability of certain features. Simple registration mechanisms can handle such a situation: It often boils down to represent an action and describe such action with some meta-data. However, ad-hoc registration mechanisms have some drawbacks: they are often not uniform and do not fit well with code navigability. In addition, metadata is not automatically synchronized with the data or behavior it describes. In this article we present the notion of pragmas, method annotations , as it was introduced in VisualWorks and now it is an important extensibility mechanism of Pharo. We present some examples of pragmas within Pharo.