diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/package.nix b/pkgs/by-name/ni/nixos-rebuild-ng/package.nix
index 02e140fcc0a6..5f75a21e2402 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/package.nix
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/package.nix
@@ -89,6 +89,8 @@ python3Packages.buildPythonApplication rec {
         ps: with ps; [
           mypy
           pytest
+          # this is to help development (e.g.: better diffs) inside devShell
+          # only, do not use its helpers like `mocker`
           pytest-mock
           ruff
         ]