  The recently-launched James Webb Space Telescope (JWST) can resolve eV-scale
emission lines arising from dark matter (DM) decay. We forecast the
end-of-mission sensitivity to the decay of axions, a leading DM candidate, in
the Milky Way using the blank-sky observations expected during standard
operations. Searching for unassociated emission lines will constrain axions in
the mass range $0.18$ eV to $2.6$ eV with axion-photon couplings
$g_{a\gamma\gamma}\gtrsim 5.5 \times 10^{-12}$ GeV$^{-1}$. In particular, these
results will constrain astrophobic QCD axions to masses $\lesssim$ 0.2 eV.
