How to turn off the nix flake registry

This is a quick tutorial on how to turn of the nix flake registry.

What is the nix flake registry?

The nix flake registry is a per-machine or per-user mapping of names to flake identifiers. For example, nixpkgs represents git://github.com/NixOS/nixpkgs. You can list yours using nix registry list.

It is what lets you write nix run nixpkgs#firefox instead of github:NixOS/nixpkgs#firefox. It also lets you use nixpkgs in your flake's outputs function without declaring it in its inputs set:

{
  inputs = {};
  outputs =
    { self
    , nixpkgs
    }: { };
}

Why would you want to turn it off?

To make sure all inputs are specified explicitly.

How to turn it off

In your NixOS configuration:

nix.registry = {};
nix.settings.flake-registry = "";

In your home manager configuration:

home-manager.users.<my-user>.xdg.configFile."nix/registry.json".text = builtins.toJSON { version = 2; };