Open learning environments (OLEs) assume that learners are good self-regulators. In such environments, learners have a large amount of control and decide on the use of different support devices (i.e. tools). However, research clearly suggests that, because students often do not possess the necessary regulation skills, they cannot decide what tool might be beneficial for their learning. This contribution deals with the impact of three metacognitive variables on tool use in OLEs: students' regulation activities; help-seeking behaviour; and instructional conceptions. Results reveal that these student characteristics affect tool use and that their impact is moderated by environmental factors, especially advice.