To cite effectsize in publications use:

Makowski D, Ben-Shachar M, Lüdecke D (2019). “Compute and interpret indices of effect size.” CRAN. R package, https://github.com/easystats/effectsize.

Corresponding BibTeX entry:

  @Article{,
    title = {Compute and interpret indices of effect size},
    author = {Dominique Makowski and Mattan S. Ben-Shachar and Daniel
      Lüdecke},
    journal = {CRAN},
    year = {2019},
    note = {R package},
    url = {https://github.com/easystats/effectsize},
  }