diff --git a/libs/sdk-py/langgraph_sdk/auth/__init__.py b/libs/sdk-py/langgraph_sdk/auth/__init__.py
index 8c8c6ad72..0050749ee 100644
--- a/libs/sdk-py/langgraph_sdk/auth/__init__.py
+++ b/libs/sdk-py/langgraph_sdk/auth/__init__.py
@@ -392,7 +392,7 @@ class _ResourceOn(typing.Generic[VCreate, VRead, VUpdate, VDelete, VSearch]):
     def __call__(
         self,
         *,
-        resources: str | Sequence[str],
+        resources: str | Sequence[str] | None = None,
         actions: str | Sequence[str] | None = None,
     ) -> Callable[
         [_ActionHandler[VCreate | VUpdate | VRead | VDelete | VSearch]],
@@ -416,25 +416,38 @@ class _ResourceOn(typing.Generic[VCreate, VRead, VUpdate, VDelete, VSearch]):
             _ActionHandler[VCreate | VUpdate | VRead | VDelete | VSearch],
         ]
     ):
-        if fn is not None:
-            _validate_handler(fn)
-            return typing.cast(
-                "_ActionHandler[VCreate | VUpdate | VRead | VDelete | VSearch]",
-                _register_handler(self.auth, self.resource, "*", fn),
-            )
-
-        def decorator(
+        def register(
             handler: _ActionHandler[VCreate | VUpdate | VRead | VDelete | VSearch],
         ) -> _ActionHandler[VCreate | VUpdate | VRead | VDelete | VSearch]:
             _validate_handler(handler)
-            return typing.cast(
-                "_ActionHandler[VCreate | VUpdate | VRead | VDelete | VSearch]",
-                _register_handler(self.auth, self.resource, "*", handler),
-            )
+            if isinstance(resources, str):
+                resource_list = [resources]
+            else:
+                resource_list = (
+                    list(resources) if resources is not None else [self.resource]
+                )
+            if resource_list != [self.resource]:
+                raise ValueError(
+                    f"Resource-specific decorator for {self.resource!r} cannot "
+                    f"register handlers for {resource_list!r}. Use @auth.on(...) "
+                    "for multiple resources."
+                )
+            if isinstance(actions, str):
+                action_list = [actions]
+            else:
+                action_list = list(actions) if actions is not None else ["*"]
+            for action in action_list:
+                _register_handler(self.auth, self.resource, action, handler)
+            return handler
 
-        # Accept keyword-only parameters for future filtering behavior; referenced to satisfy linters.
-        _ = resources, actions
-        return decorator
+        if fn is not None:
+            return register(
+                typing.cast(
+                    "_ActionHandler[VCreate | VUpdate | VRead | VDelete | VSearch]",
+                    fn,
+                )
+            )
+        return register
 
 
 class _AssistantsOn(
diff --git a/libs/sdk-py/tests/test_auth.py b/libs/sdk-py/tests/test_auth.py
new file mode 100644
index 000000000..6f06be472
--- /dev/null
+++ b/libs/sdk-py/tests/test_auth.py
@@ -0,0 +1,44 @@
+import pytest
+
+from langgraph_sdk import Auth
+
+
+def _handler():
+    async def handler(ctx, value):
+        return ctx is not None and value is not None
+
+    return handler
+
+
+def test_resource_decorator_registers_specific_actions():
+    auth = Auth()
+
+    handler = auth.on.threads(actions=["read", "search"])(_handler())
+
+    assert auth._handlers == {
+        ("threads", "read"): [handler],
+        ("threads", "search"): [handler],
+    }
+
+
+def test_resource_decorator_registers_single_action():
+    auth = Auth()
+
+    handler = auth.on.threads(actions="read")(_handler())
+
+    assert auth._handlers == {("threads", "read"): [handler]}
+
+
+def test_resource_decorator_without_actions_registers_resource_wildcard():
+    auth = Auth()
+
+    handler = auth.on.threads(_handler())
+
+    assert auth._handlers == {("threads", "*"): [handler]}
+
+
+def test_resource_decorator_rejects_mismatched_resources():
+    auth = Auth()
+
+    with pytest.raises(ValueError, match=r"Use @auth\.on"):
+        auth.on.threads(resources="assistants", actions="read")(_handler())