{
  lib,
  snow,
  ...
}: let
  inherit
    (lib)
    mkOption
    types
    ;
  inherit
    (snow.lib)
    mkPerSystemFlakeOutput
    ;
in
  mkPerSystemFlakeOutput {
    name = "formatter";
    option = mkOption {
      type = types.nullOr types.package;
      default = null;
      description = ''
        A package used by [`nix fmt`](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-fmt.html).
      '';
    };
    file = ./apps.nix;
  }