The rise of large-scale collaborative panel studies has generated a need for fast, reliable, and valid assessments of cognitive abilities. In these studies, a detailed characterization of participants' cognitive abilities is often unnecessary, leading to the selection of tests based on convenience, duration, and feasibility. This often results in the use of abbreviated measures or proxies, potentially compromising their reliability and validity. Here we evaluate the mini-q (Baudson & Preckel, 2016), a three-minute speeded reasoning test, as a brief assessment of general cognitive abilities. The mini-q exhibited excellent reliability (0.96–0.99) and a substantial correlation with general cognitive abilities measured with a comprehensive test battery (r = 0.57; age-corrected r = 0.50), supporting its potential as a brief screening of cognitive abilities. Working memory capacity accounted for the majority (54%) of the association between test performance and general cognitive abilities, whereas individual differences in processing speed did not contribute to this relationship. Our results support the notion that the mini-q can be used as a brief, reliable, and valid assessment of general cognitive abilities. We therefore developed a computer-based version, ensuring its adaptability for large-scale panel studies. The paper- and computer-based versions demonstrated scalar measurement invariance and can therefore be used interchangeably. We provide norm data for young (18 to 30 years) and middle-aged (31 to 60 years) adults and provide recommendations for incorporating the mini-q in panel studies. Additionally, we address potential challenges stemming from language diversity, wide age ranges, and online testing in such studies.