  We sharpen Swampland constraints on 8d supergravity theories by studying
consistency conditions on worldvolume theory of 3-brane probes. Combined with a
stronger form of the cobordism conjecture, this leads to the reconstruction of
the compact internal geometry and implies strong restrictions on the gauge
algebra and on some higher derivative terms (related to the level of the
current algebra on the 1-brane). In particular we argue that 8d supergravity
theories with $\mathfrak{g}_2$ gauge symmetry are in the Swampland. These
results provide further evidence for the string lamppost principle in 8d with
16 supercharges.
