Objective: Determine the validity of the TRT_S 2012 software in to assess the total reaction time (TRT) with a simple visual stimulus (TRTSimple) and mental fatigue from TRT (TRTFatigue). Methods: Three types of validation were applied: a) concurrent, for determining the correlation between the TRT_S 2012 Software and Vienna Test System (VTS), b) content of a sample of adults, and c)mechanical, using a robot that performs a mechanic motion to respond to a light stimulus.The study included 216 young adults, college students aged 17 -45 years (x = 24.0 ± 6.0) and a robot. Descriptive and inferential statistics were used for performance on TRT obtained by young adults and robot in two software. Results: The intra-class correlation in the adults TRT showed strong correlation between VTS and TRTSimple (R = .72). Identification of the proposed initial stimulus in TRTFatigue presented intermediate correlation with VTS (R = .56) and the final stimulus presented low correlation with VTS (R=.35).The robot TRT showed standard deviation ranging .5 ms (on average) between the highest and lowest.The standard error of the mean ranged from .23 to .28 and the distributions were homogeneous between 8.2 to 9.7%. Conclusion: The results confirmed the validity of the software TRT_S 2012 . It is a reliable cognitive test that can be applied to young adults for measuring the TRT with simple visual stimuli and for evaluating the influence of mental fatigue from the TRT. however, the delays caused by the computer resources used should be considered and measured with a resource like the robot. We conclude that the TRT_S 2012 software is valid for assessing the TRT and cognitive fatigue in healthy adults.Key words: reaction time, mental fatigue, software.