GlycoMod ( http://www.expasy.org /tools/glycomod/) (1) is a computational tool that finds all possible compositions of a glycan structure from its experimentally determined mass. It may be used to calculate the possible compositions of free or derivatized glycan structures, or compositions of glycans attached to glycoproteins and glycopeptides. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.