  A growing number of two-dimensional superconductors are being discovered in
the family of layered van der Waals (vdW) materials. Due to small sample
volume, their characterization has been largely limited to electrical transport
measurements. As a consequence, characterization of the diamagnetic response of
the superfluid to an applied magnetic field, a defining property of any
superconductor, has been lacking. Here, we use a local magnetic probe to
directly measure the superfluid response of the tunable, gate-induced
superconducting state in MoS$_2$. We find that the backgate changes the
superconducting transition temperature non-monotonically whereas the superfluid
stiffness at low temperature and the normal state conductivity monotonically
increase with backgate voltage. In some devices, we find direct signatures in
agreement with a Berezinskii-Kosterlitz-Thouless transition, whereas in others
we find a broadened, shallow onset of the superfluid response. We show that the
observed behavior is consistent with disorder playing an important role in
determining the superconducting properties in superconducting MoS$_2$. Our work
demonstrates that magnetic property measurements are within reach for vdW
superconductors and reveals that the superfluid response significantly deviates
from simple BCS-like behavior.
