There is considerable anecdotal evidence suggesting that software engineers enjoy engaging in solving puzzles and other cognitive efforts. A tendency to engage in and enjoy effortful thinking is referred to as a person’s ‘need for cognition.’ In this article we study the relationship between software engineers’ personality traits and their need for cognition. Through a large-scale sample study of 483 respondents we collected data to capture the six ‘bright’ personality traits of the HEXACO model of personality, and three ‘dark’ personality traits. Data were analyzed using several methods including a multiple Bayesian linear regression analysis. The results indicate that ca. 33% of variation in developers’ need for cognition can be explained by personality traits. The Bayesian analysis suggests four traits to be of particular interest in predicting need for cognition: openness to experience, conscientiousness, honesty-humility, and emotionality. Further, we also find that need for cognition of software engineers is, on average, higher than in the general population, based on a comparison with prior studies. Given the importance of human factors for software engineers’ performance in general, and problem solving skills in particular, our findings suggest several implications for recruitment, working behavior, and teaming.