To cite the DeclareDesign software, cite the package itself. To cite the design framework it implements, cite Blair, Coppock and Humphreys (2023) for the book-length treatment or Blair, Cooper, Coppock and Humphreys (2019) for the article. Citing the package and the framework are different acts and either may be what you want.

Coppock A, Blair G, Cooper J, Humphreys M, Fultz N (2026). DeclareDesign: A Tidyverse-First Research Design Declaration and Diagnosis Tool. R package version 2.0.0, https://declaredesign.org/r/declaredesign/.

Blair G, Coppock A, Humphreys M (2023). Research Design in the Social Sciences: Declaration, Diagnosis, and Redesign. Princeton University Press, Princeton. https://book.declaredesign.org.

Blair G, Cooper J, Coppock A, Humphreys M (2019). “Declaring and Diagnosing Research Designs.” American Political Science Review, 113, 838-859. https://declaredesign.org/paper.pdf.

Corresponding BibTeX entries:

  @Manual{DeclareDesign,
    title = {DeclareDesign: A Tidyverse-First Research Design
      Declaration and Diagnosis Tool},
    author = {Alexander Coppock and Graeme Blair and Jasper Cooper and
      Macartan Humphreys and Neal Fultz},
    year = {2026},
    note = {R package version 2.0.0},
    url = {https://declaredesign.org/r/declaredesign/},
  }

  @Book{blair_coppock_humphreys_2023,
    title = {Research Design in the Social Sciences: Declaration,
      Diagnosis, and Redesign},
    author = {Graeme Blair and Alexander Coppock and Macartan
      Humphreys},
    publisher = {Princeton University Press},
    address = {Princeton},
    year = {2023},
    url = {https://book.declaredesign.org},
  }

  @Article{blair_cooper_coppock_humphreys_2019,
    title = {Declaring and Diagnosing Research Designs},
    author = {Graeme Blair and Jasper Cooper and Alexander Coppock and
      Macartan Humphreys},
    journal = {American Political Science Review},
    volume = {113},
    issue = {3},
    pages = {838-859},
    year = {2019},
    url = {https://declaredesign.org/paper.pdf},
  }