{
  inputs = {
    nixpkgs.url = github:squarepear/nixpkgs/gdtoolkit-4;
    treefmt-nix.url = github:numtide/treefmt-nix;
  };

  outputs = {
    self,
    nixpkgs,
    systems,
    treefmt-nix,
  }: let
    # Small tool to iterate over each systems
    eachSystem = f: nixpkgs.lib.genAttrs (import systems) (system: f nixpkgs.legacyPackages.${system});

    # Eval the treefmt modules from ./treefmt.nix
    treefmtEval = eachSystem (pkgs: treefmt-nix.lib.evalModule pkgs ./treefmt.nix);
  in {
    # for `nix fmt`
    formatter = eachSystem (pkgs: treefmtEval.${pkgs.system}.config.build.wrapper);
    # for `nix flake check`
    checks = eachSystem (pkgs: {
      formatting = treefmtEval.${pkgs.system}.config.build.check self;
    });
  };
}