When using the ESM-Tools, please cite the software by using the following DOI: https://zenodo.org/doi/10.5281/zenodo.3737927. This DOI represents all versions of the software, and will always points to the latest version on zenodo. If you navigate to that page you can also find the DOIs for each specific version, in the Versions panel.
Further information on available versions of the software can be found here.