  Context: Angular momentum (AM) transport models of stellar interiors require
improvements to explain the strong extraction of AM from stellar cores that is
observed with asteroseismology. One of the often invoked mediators of AM
transport are internal magnetic fields, even though their properties,
observational signatures and influence on stellar evolution are largely
unknown.
  Aims: We study how a fossil, axisymmetric internal magnetic field affects
period spacing patterns of dipolar gravity mode oscillations in main-sequence
stars with masses of 1.3, 2.0 and 3.0 M$_\odot$. We assess the influence of
fundamental stellar parameters on the magnitude of pulsation mode frequency
shifts.
  Methods: We compute dipolar gravity mode frequency shifts due to a fossil,
axisymmetric poloidal-toroidal internal magnetic field for a grid of stellar
evolution models, varying stellar fundamental parameters. Rigid rotation is
taken into account using the traditional approximation of rotation and the
influence of the magnetic field is computed using a perturbative approach.
  Results: We find magnetic signatures for dipolar gravity mode oscillations in
terminal-age main-sequence stars that are measurable for a near-core field
strength larger than $10^{5}$ G. The predicted signatures differ appreciably
from those due to rotation.
  Conclusions: Our formalism demonstrates the potential for the future
detection and characterization of strong fossil, axisymmetric internal magnetic
fields in gravity-mode pulsators near the end of core-hydrogen burning from
Kepler photometry, if such fields exist.
