  We make an explicit link between the cubic interactions of off-shell fields
and the on-shell three-point amplitudes in four dimensions. Both the cubic
interactions and the on-shell three-point amplitudes had been independently
classified in the literature, but their relation has not been made explicit.
The aim of this note is to provide such a relation and discuss similarities and
differences of their constructions. For the completeness of our analysis, we
also derive the covariant form of all parity-odd massless vertices.
