diff --git a/flake.nix b/flake.nix
index dc1cd72..d4f5f9e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -92,6 +92,15 @@
               inherit pkgs;
             };
           };
+
+          # A working shell for developing skills in this repo.
+          # python3 runs the benchmark skill's deterministic core.
+          # The benchmark-skill is placed into ./.claude/skills/ on entry, so
+          # /benchmark-skill is available while working in this repo.
+          devShells.default = pkgs.mkShell {
+            packages = [ pkgs.python3 ];
+            shellHook = mkSkillsShellHook [ (skillPackages pkgs).benchmark-skill ];
+          };
         }
       );
 }