This study investigates the impact of different design tools on designers’ metacognitive behavior, specifically examining the differences between generative AI tools and traditional image collection tools in the design process. A qualitative research approach was adopted, utilizing video recordings and interviews to explore the relationship between students’ use of different tools and their metacognitive engagement in design. The study involved four senior undergraduate students, who were divided into an experimental group (Midjourney) and a control group (Pinterest). Participants were assigned a design task and engaged in a rapid design session. Subsequently, they reviewed the recorded design process together with the researcher and participated in a retrospective think-aloud interview. The interview transcripts were then coded for design processes and metacognitive activities for analysis. The results indicate that designers using AI tools tend to establish design goals quickly, focus on product-related detail refinement, and exhibit higher action efficiency. However, they also demonstrated more explicit decision-making with fewer modifications during the process, suggesting that AI tools may reduce designers’ fine-tuned adjustments and strategic evaluations in creative exploration. In contrast, designers using traditional tools engaged in more frequent reflections on the design process and exhibited a higher level of metacognitive behavior related to strategic adjustments and creative exploration. These findings suggest that different tools may influence designers’ cognitive patterns and decision-making processes. Future research could further explore the influence of tools across various design domains or integrate physiological to analyze designers’ decision-making processes in different tool usage contexts, deepening the understanding of design behavior and metacognition.