The sequence-dependent statistical mechanics of double-stranded nucleic acid, or dsNA, is believed to be essential in its biological functions. In turn, the equilibrium statistical mechanics behaviour of dsNA depends strongly both on sequence-dependent perturbations in its ground state shape away from an idealised, uniform, double-helical configuration, and on its fluctuations as governed by its sequence-dependent stiffness. We here describe the cgNA+web browser-based interactive tool for visualising the sequence-dependent ground states of dsNA fragments of arbitrary sequences, as predicted by the underlying cgNA+ coarse-grain model. Parameter sets are provided to model dsDNA, including the possibility of epigenetically modified CpG dinucleotide steps, dsRNA, and DNA:RNA Hybrid double helical fragments. The cgNA+web interface is specifically designed to compare ground state shapes of different sequences of the same dsNA, or analogous sequences of different dsNAs. The cgNA+web server is freely available at cgDNAweb.epfl.ch without any login requirement. (c) 2023 The Authors. Published by Elsevier Ltd.