  We present a package for the computer algebra system Mathematica, which
implements the parametrized post-Newtonian (PPN) formalism. This package, named
xPPN, is built upon the widely used tensor algebra package suite xAct, and in
particular the package xTensor therein. The main feature of xPPN is to provide
functions to perform a proper $3+1$ decomposition of tensors, as well as a
perturbative expansion in so-called velocity orders, which are central tasks in
the PPN formalism. Further, xPPN implements various rules for quantities
appearing in the PPN formalism, which aid in perturbatively solving the field
equations of any metric theory of gravity. Besides Riemannian geometry, also
teleparallel and symmetric teleparallel geometry are implemented.
