Objective: Little is known about the impact of mechanical feedback in self-care support tools. Technically, natural language processing and machine learning can provide mechanical feedback in self-care support tools. This study compared the differences between mechanical feedback and no feedback conditions in a self-care support tool based on solutionfocused brief therapy. In the feedback condition, feedback was provided by mechanically determining the probability that the goal answered in goal setting was concrete or realistic. Methods: A total of 501 participants were recruited and randomly assigned to either the feedback (n = 268) or no feedback (n = 233) condition. Results: The results showed that the mechanical feedback increased the probability of problem-solving. In contrast, solution-building, positive and negative affect, and the probability of living an ideal life increased when using the self-care support tool based on solution-focused brief therapy, regardless of the feedback. In addition, the higher the probability of goal concreteness and reality, the greater the improvement in solution-building and positive affect. Conclusion: This study suggests that self-care support tools based on solution-focused brief therapy with feedback are more effective than those without feedback. Self-care support tools based on solution-focused brief therapy with feedback can be used as an easily accessible tool to maintain and promote mental health. [ABSTRACT FROM AUTHOR]