Acting is an important decisional function for autonomous robots. Acting relies on skills to implement and to model the activities it oversees: refinement, local recovery, temporal dis- patching, external asynchronous events, and commands execution, all done online. While sitting between planning and the robotic platform, acting often relies on programming primitives and an interpreter which executes these skills. Following our experience in providing a formal framework to program the functional components of our robots, we propose a new language, to program the acting skills. This language maps unequivocally into a formal model which can then be used to check properties offline or execute the skills, or more precisely their formal equivalent, and per- form runtime verification. We illustrate with a real example how we can program a survey mission for a drone in this new language, prove some formal properties on the program and directly exe- cute the formal model on the drone to perform the mission.