Abstract: Context: Code review is a fundamental, yet expensive part of software engineering. Therefore, research on understanding code review and its efficiency and performance is paramount.Objective: We aim to test the effect of a guidance approach on review effectiveness and efficiency. This effect is expected to work by lowering the cognitive load of the task; thus, we analyze the mediation relationship as well.Method: To investigate this effect, we employ an experimental design where professional developers have to perform three code reviews. We use three conditions: no guidance, a checklist, and a checklist-based review strategy. Furthermore, we measure the reviewers’ cognitive load.Limitations: The main limitations of this study concern the specific cohort of participants, the mono-operation bias for the guidance conditions, and the generalizability to other changes and defects. Full registered report: https://doi.org/10.17605/OSF.IO/5FPTJ; Materials: https://doi.org/10.6084/m9.figshare.11806656