diff --git a/shell.nix b/shell.nix
index 761e3a3..1ca9028 100644
--- a/shell.nix
+++ b/shell.nix
@@ -7,5 +7,6 @@ with pkgs;
     buildInputs = [
       nix # Powerful package manager, makes packaging reliable & reproducible
       tea # Gitea official CLI client
+      treefmt # one CLI to format the code tree
     ];
   }