To cite package ‘swirl’ in publications use:

Kross S, Carchedi N, Bauer B, Grdina G (2020). swirl: Learn R, in R. R package version 2.4.5, https://CRAN.R-project.org/package=swirl.

Corresponding BibTeX entry:

  @Manual{,
    title = {swirl: Learn R, in R},
    author = {Sean Kross and Nick Carchedi and Bill Bauer and Gina
      Grdina},
    year = {2020},
    note = {R package version 2.4.5},
    url = {https://CRAN.R-project.org/package=swirl},
  }