The source code is freely available on GitHub () and will be made available as a web service at molcalc.org in the near future. Figure : An example of the output of RegioSQM20. Tautomers are depicted with relative energies (only including those below 15 kcal/mol) along with an estimate of their reactivity based on the highest proton affinity. The highlighted atoms represent the predicted EAS sites within 1 kcal/mol (green circles) and the EAS sites within 3 kcal/mol (red circles). RegioSQM correlates proton affinity with EAS reactivity. The green and red dots indicate the atoms with proton affinities within 1 and 3 kcal/mol of the highest value, respectively. The black dots indicate the experimentally observed sites for EAS. All experimentally observed sites must be predicted by green dots to be counted as correct.