This article reports on the realization and on first applications of the Cadyts (Calibration of dynamic traffic simulations) calibration tool. The presented first version of Cadyts calibrates disaggregate demand models of dynamic traffic assignment simulators from traffic counts. The tool is broadly applicable in that it (i) makes only very mild assumptions about the calibrated simulator's workings and (ii) allows for various modes of technical interaction with the simulation software. The article provides a both conceptual and technical overview of the tool and exemplary demonstrates its applicability to two different traffic microsimulators.