Akin to electronic systems that can tune to and process signals of select frequencies, systems/networks of chemical reactions also „propagate“ time‐varying concentration inputs in a frequency‐dependent manner. Whereas signals of low frequencies are transmitted, higher frequency inputs are dampened and converted into steady‐concentration outputs. Such behavior is observed in both idealized reaction chains as well as realistic signalling cascades, in the latter case explaining the experimentally observed responses of such cascades to input calcium oscillations. These and other results are supported by numerical simulations within the freely available Kinetix web application we developed to study chemical systems of arbitrary architectures, reaction kinetics, and boundary conditions. (c) 2013 Weily-VCH Verlag GmbH & Co. KgaA, Weinheim