The belief update task has been used by many scientists to test a wide range of questions related to belief formation and optimism. Most of these studies are rigorous and well conducted. However, a small number of researchers have used the task inappropriately, inserting new confounds and failing to control for other potential ones. This has resulted in the report of false findings which have muddied the literature. We thus created a guide to help scientists who would like to use the belief update task, as well as readers and reviewers who are required to evaluate studies using this task.