Autonomy is an inherent condition of every ethical act. This attribution is expressed, when decisions are made, as capacity. Physician-patient alliance is defied when there is a reasonable doubt of patients’ ability to make a choice, an extraordinarily complex scenario. As a response, in the last few decades multiple tools have been developed aiming to determine in a standardized fashion whether capacity is present or not. In the present article, we present a classification of the most well-known tools and discuss their usefulness, the implications for standardization of capacity, and make recommendations for their use, based in evidence.