{
  inputs,
  pkgs,
  ...
}:
{
  nixpkgs.overlays = [
    (_: prev: {
      # include nixpkgs stable
      stable = import inputs.nixpkgs-stable {
        inherit (prev.pkgs) system;
        config.allowUnfree = true;
      };

      # include custom packages
      custom =
        (prev.custom or { })
        // (import ../packages {
          inherit (prev) pkgs;
          inherit inputs;
        });

      # use nixfmt-rfc-style as the default
      nixfmt = prev.nixfmt-rfc-style;
    })
  ];
}