Environmental DNA metabarcoding is at the same time similar and different with the classical taxonomical DNA Barcoding. The aims of environmental studies and the technical constraints oblige most of the time to compare several sets of primers and eventually to design new primers dedicated to a specific study. I will discuss during this presentation about bioinformatics approaches allowing an objective estimation of the relative qualities of several PCR primer pairs. Based on these method, it is possible to develop software selecting new primer pairs by maximizing these criteria in the context of a set of experimental constraints defined by the biologist.