You can use nix without using nixpkgs (you seemed to be trying to use nixpkgs). The nix language is accessible via several command line tools, nix repl, nix eva

You can use nix without using nixpkgs (you seemed to be trying to use nixpkgs). The nix language is accessible via several command line tools, nix repl, nix eval, nix-instantiate, etc, and can emit json via everal flags, as well as a builtin function.