  SPINAS is a C++ package created for the implementation and numerical
computation of phase-space points of constructive amplitudes in particle
physics. This package contains a suite of classes and methods for handling
particles, propagators, spinor products, and processes. SPINAS is structured to
offer straightforward usability while ensuring maximum efficiency. This is
achieved through a design that emphasizes the storage and reuse of intermediate
results within amplitude calculations for each phase-space point. We include a
user guide describing how to use the components, a complete example of how to
use SPINAS for a scattering amplitude, a discussion of the design and
implementation useful for those wishing to contribute, and a discussion of our
validation of this package, including both a validation of individual
components of the package and a comparison of a complete set of Standard Model
processes with Feynman diagrams.
