{
  inputs = {
    nixstable.url = "nixpkgs/21.05";
    nixpkgs.url = "nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, nixstable, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
        stable = nixstable.legacyPackages.${system};
      in {
        devShell = pkgs.mkShell {
          buildInputs = [
            pkgs.epubcheck
            pkgs.nixfmt
            pkgs.nodejs-16_x
            pkgs.pandoc
            pkgs.pdftk
            pkgs.python39Full
            pkgs.python39Packages.weasyprint
            pkgs.jq
            pkgs.s3cmd
          ];
        };
      });
}