{
  description = "books";
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";
    pre-commit-hooks.inputs.nixpkgs.follows = "nixpkgs";
    pre-commit-hooks.url = "github:cachix/pre-commit-hooks.nix";
  };

  outputs =
    inputs:
    let
      inherit (inputs.nixpkgs) lib;
      forAllSystems =
        f:
        lib.genAttrs lib.systems.flakeExposed (
          system:
          f rec {
            inherit system;
            pkgs = inputs.nixpkgs.legacyPackages.${system};
          }
        );
    in
    {
      # nix -L build .#hello
      packages = forAllSystems ({ pkgs, ... }: pkgs);

      # nix -L develop  or  direnv allow
      devShell = forAllSystems (
        {
          pkgs,
          system,
          ...
        }:
        pkgs.mkShell {
          name = "shell";
          src = null;
          buildInputs = [
            pkgs.fontconfig
            #pkgs.gitFull
            pkgs.jq
            pkgs.pandoc
            pkgs.reuse
            pkgs.shellcheck
          ];
          inherit (inputs.self.checks.${system}.pre-commit-check) shellHook;
        }
      );

      # nix flake check
      checks = forAllSystems (
        args: with args; {
          pre-commit-check = inputs.pre-commit-hooks.lib.${system}.run {
            src = inputs.self;
            hooks = {
              nixfmt-rfc-style.enable = true;
            };
          };
        }
      );
    };
}