In ecotoxicology, bioassays are standardly conducted in order to measure acute or chronic effects of potentially toxic substances on reproduction, growth, and/or survival of living animals. MOSAIC, standing for MOdeling and StAtistical tools for ecotoxICology, is a user-friendly web interface dedicated to the mathematical and statistical modelling of such standard bioassay data. Its simple use makes MOSAIC a turnkey decision-making tool for ecotoxicologists and regulators in support of their daily when they evaluate dossiers of marketing authorisation of active substances.