An example skeleton for Nix development environments using the flake default package.

flake.nix

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

    outputs = { self, nixpkgs, flake-utils }:
        flake-utils.lib.simpleFlake {
            inherit self nixpkgs;
            name = "joker";
            shell = ./shell.nix;
            systems = ["x86_64-linux" "x86_64-darwin"];
        };
    }

shell.nix

{ pkgs ? import <nixpkgs> }:
pkgs.mkShell {
    buildInputs = [ pkgs.jq ];
}