Relaxase-based plasmid classification has become popular in the past 10 years. Nevertheless, it is not obvious how to assign a query protein to a relaxase MOB family. Automated protein annotation is commonly used to classify them into families, gathering evolutionarily related proteins that likely perform the same function, while circumventing the problem of different naming conventions. Here, we implement an automated method, MOBscan, to identify relaxases and classify them into any of the nine MOB families. MOBscan is a web tool that carries out a HMMER search against a curated database of MOB profile Hidden Markov models. It is freely available at https://castillo.dicom.unican.es/mobscan/ .