Motivation: More than 20 years ago, our laboratory published an original statistical test [referred to as the Audic-Claverie (AC) test in the literature] to identify differentially expressed genes from the pairwise comparison of counts of 'expressed sequence tags' determined in different conditions. Despite its antiquity and the publications of more sophisticated packages, this original publication continued to gather more than 200 citations per year, indicating the persistent usefulness of the simple AC test for the community. This prompted us to propose a fully revamped version of the AC test with a user interface adapted to the diverse and much larger datasets produced by contemporary omics techniques. Results: ACDtool is a freely accessible web-service proposing three types of analyses: (i) the pairwise comparison of individual counts, (ii) pairwise comparisons of arbitrary large lists of counts and (iii) the all-at-once pairwise comparisons of multiple datasets. Statistical computations are implemented using standard R functions and can accommodate all practical ranges of counts as generated by modern omic experiments. ACDtool is well suited for large datasets without replicates. Availability and implementation: http://www.igs.cnrs-mrs.fr/acdtool/. Supplementary information: Supplementary data are available at Bioinformatics online.