  Context: Seasonal variations and climate stability of a planet are very
sensitive to the planet obliquity and its evolution. This is of particular
interest for the emergence and sustainability of land-based life, but orbital
and rotational parameters of exoplanets are still poorly constrained. Numerical
explorations usually realised in this situation are thus in heavy contrast with
the uncertain nature of the available data.
  Aims: We aim to provide an analytical formulation of the long-term spin-axis
dynamics of exoplanets, linking it directly to physical and dynamical
parameters, but still giving precise quantitative results if the parameters are
well known. Together with bounds for the poorly constrained parameters of
exoplanets, this analysis is designed to allow a quick and straightforward
exploration of the spin-axis dynamics.
  Methods: The long-term orbital solution is decomposed in quasi-periodic
series and the spin-axis Hamiltonian is expanded in powers of eccentricity and
inclination. Chaotic zones are measured by the resonance overlap criterion.
Bounds for the poorly known parameters of exoplanets are obtained from physical
grounds (rotational breakup) and dynamical considerations (equipartition of
AMD).
  Results: This method gives accurate results when the orbital evolution is
well known. The chaotic zones for planets of the Solar System can be retrieved
in details from simple analytical formulas. For less constrained planetary
systems, the maximal extent of the chaotic regions can be computed, requiring
only the mass, the semi-major axis and the eccentricity of the planets present
in the system. Additionally, some estimated bounds of the precession constant
allow to classify which observed exoplanets are necessarily out of major
spin-orbit secular resonances (unless the precession rate is affected by the
presence of massive satellites).
