To cite package ‘swirlify’ in publications use:

  Kross S, Carchedi N (2019). _swirlify: A Toolbox for Writing 'swirl'
  Courses_. R package version 0.5.3,
  <https://CRAN.R-project.org/package=swirlify>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {swirlify: A Toolbox for Writing 'swirl' Courses},
    author = {Sean Kross and Nick Carchedi},
    year = {2019},
    note = {R package version 0.5.3},
    url = {https://CRAN.R-project.org/package=swirlify},
  }