  We show that there are four chiral ${\cal W}$-algebra extensions of
$\mathfrak{so}(2,3)$ algebra and construct them explicitly. We do this by a
simple identification of each of the inequivalent embeddings of a copy of
$\mathfrak{sl}(2,{\mathbb R})$ in the $\mathfrak{so}(2,3)$ algebra and the
maximal subalgebra $\mathfrak{h}$ that commutes with it. Then using the
standard 2d chiral CFT techniques we find the corresponding ${\cal W}$-algebra
extensions. Two of the four resultant ${\cal W}$-algebras are new, one of which
may be thought of as the conformal $\mathfrak{bms}_3$ algebra valid for finite
values of its central charge.}
