{
  # Defines a minimal NixOS module with one option and one config effect,
  # exposes it as `nixosModules.default`, and verifies it by evaluating a
  # throwaway NixOS configuration that imports the module.
  description = "A minimal NixOS module";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };

  outputs =
    { self, nixpkgs, ... }:
    let
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.${system};

      # Throwaway NixOS configuration used only by the check below.
      # We never build `system.build.toplevel`, so bootloader and
      # `fileSystems` assertions never fire; reading a single config
      # attribute is enough to prove the module evaluates.
      testConfig = nixpkgs.lib.nixosSystem {
        inherit system;
        modules = [
          self.nixosModules.default
          {
            system.stateVersion = "24.11";
            playground.greeter = {
              enable = true;
              name = "flakes";
            };
          }
        ];
      };
    in
    {
      # Other flakes consume the module via:
      #   imports = [ inputs.nix-playground.nixosModules.default ];
      nixosModules.default = import ./module.nix;

      # Builds only if the merged config's greeting matches expectation.
      checks.${system}.greeting =
        pkgs.runCommand "greeting-check"
          {
            got = testConfig.config.environment.etc."greeting".text;
            expected = "hello, flakes";
          }
          ''
            if [ "$got" = "$expected" ]; then
              echo ok > $out
            else
              echo "unexpected greeting: $got" >&2
              exit 1
            fi
          '';
    };
}