Web accessibility is that feature that allows anyone, regardless of their conditions, to access the contents of websites. The use of automatic validators allows a first analysis to be made about the level of accessibility of a website. However, the selection of these tools tends not to be trivial due to the technical differences presented by each validator. The objective of this work was to carry out a comparative analysis between automatic accessibility validators, seeking to establish selection criteria when choosing a validator to carry out an accessibility evaluation. A methodology was proposed based on three stages that allowed the selection of 14 validators that were analyzed under different criteria. In addition, it allowed to conclude that none of the analyzed validators fulfills all the characteristics, reason why it would not be enough to select only one to carry out an accessibility evaluation process. Therefore, this methodological process constitutes a very useful tool for the selection of accessibility validators.