Since there is now a growing wish by referees to judge the underpinning data for a submitted article, it is timely to provide a summary of the data evaluation checks required to be done by a referee. As these checks will vary from field to field, this article focuses on the needs of biological X-ray crystallography articles, which is the predominantly used method leading to depositions in the PDB. These checks necessarily include that a referee scrutinizes the PDB validation report for each crystal structure accompanying the article submission. A referee would also undertake one cycle of model refinement of the authors' biological macromolecule coordinates against the authors' processed diffraction data and assess the model and Fo-Fc electron density maps. If the referee deems necessary, the raw diffraction data images should be reprocessed (e.g. to a different diffraction resolution). The organization of practical referee skills training can be via the crystallography associations.