  Modelling the broadband emission of jetted active galactic nuclei (AGN)
constitutes one of the main research topics of extragalactic astrophysics in
the multi-wavelength and multi-messenger domain.
  We present agnpy, an open-source python package modelling the radiative
processes of relativistic particles accelerated in the jets of active galactic
nuclei. The package includes classes describing the galaxy components
responsible for line and thermal emission and calculates the absorption due to
$\gamma\gamma$ pair production on several photon fields. agnpy aims at
extending the effort of modelling and interpreting the emission of
extragalactic sources to a wide number of astrophysicists.
  We present the package content and illustrate a few examples of applications
of its functionalities. We validate the software by comparing its results
against the literature and against other open-source software.
  We illustrate the utility of agnpy in addressing the most common questions
encountered while modelling the emission of jetted active galaxies. When
comparing its results against the literature and other modelling tools adopting
the same physical assumptions, we achieve an agreement within $10-30\%$.
  agnpy represents one of the first systematic and validated collection of
established radiative processes for jetted active galaxies in an open-source
python package. We hope it will stand also among the first endeavours providing
reproducible and transparent astrophysical software not only for data reduction
and analysis, but also for modelling and interpretation.

Instrumentation and Methods for Astrophysics;Astrophysics of Galaxies;High Energy Astrophysical Phenomena