  We study the consistency conditions for interactions of massless fields of
any spin in four-dimensional flat space using the light-cone approach. We show
that they can be equivalently rewritten as the Ward identities for the
off-shell light-cone amplitudes built from the light-cone Hamiltonian in the
standard way. Then we find a general solution of these Ward identities. The
solution admits a compact representation when written in the spinor-helicity
form and is given by an arbitrary function of spinor products, satisfying
well-known homogeneity constraints. Thus, we show that the light-cone
consistent deformation procedure inevitably leads to a certain off-shell
version of the spinor-helicity approach. We discuss how the relation between
the two approaches can be employed to facilitate the search of consistent
interaction of massless higher-spin fields.
