diff --git a/MANIFEST.in b/MANIFEST.in
index 2971d2a..1c827de 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,6 +1,7 @@
 include README.md
 include LICENSE
 include CHANGELOG.md
+include spinstep/py.typed
 recursive-exclude benchmark *
 recursive-exclude demos *
 recursive-exclude examples *
diff --git a/spinstep/discrete.py b/spinstep/discrete.py
index 48ab185..f84b07b 100644
--- a/spinstep/discrete.py
+++ b/spinstep/discrete.py
@@ -6,6 +6,8 @@
 
 from __future__ import annotations
 
+__all__ = ["DiscreteOrientationSet"]
+
 from typing import Any
 
 import numpy as np
diff --git a/spinstep/discrete_iterator.py b/spinstep/discrete_iterator.py
index 0bc7075..5632a37 100644
--- a/spinstep/discrete_iterator.py
+++ b/spinstep/discrete_iterator.py
@@ -6,6 +6,8 @@
 
 from __future__ import annotations
 
+__all__ = ["DiscreteQuaternionIterator"]
+
 from typing import Iterator, List, Set, Tuple
 
 import numpy as np
diff --git a/spinstep/node.py b/spinstep/node.py
index e4cbd6d..a98846d 100644
--- a/spinstep/node.py
+++ b/spinstep/node.py
@@ -6,6 +6,8 @@
 
 from __future__ import annotations
 
+__all__ = ["Node"]
+
 from typing import List, Optional, Sequence
 
 import numpy as np
diff --git a/spinstep/py.typed b/spinstep/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/spinstep/traversal.py b/spinstep/traversal.py
index bde9cf4..5a61851 100644
--- a/spinstep/traversal.py
+++ b/spinstep/traversal.py
@@ -6,6 +6,8 @@
 
 from __future__ import annotations
 
+__all__ = ["QuaternionDepthIterator"]
+
 from typing import Iterator, List, Optional, Tuple
 
 import numpy as np
diff --git a/spinstep/utils/__init__.py b/spinstep/utils/__init__.py
index 4d602f2..2f41c50 100644
--- a/spinstep/utils/__init__.py
+++ b/spinstep/utils/__init__.py
@@ -2,4 +2,40 @@
 # Author: Eraldo B. Marques <eraldo.bernardo@gmail.com> — Created: 2025-05-14
 # See LICENSE.txt for full terms. This header must be retained in redistributions.
 
-"""Internal utilities for quaternion math and array backend selection."""
+"""Utilities for quaternion math and array backend selection.
+
+This sub-package provides:
+
+- :func:`~.array_backend.get_array_module` — NumPy / CuPy backend selection.
+- :func:`~.quaternion_math.batch_quaternion_angle` — batch angular distances.
+- Quaternion helpers in :mod:`~.quaternion_utils` (conversion, distance,
+  multiplication, etc.).
+"""
+
+__all__ = [
+    "get_array_module",
+    "batch_quaternion_angle",
+    "quaternion_from_euler",
+    "quaternion_distance",
+    "rotate_quaternion",
+    "is_within_angle_threshold",
+    "quaternion_conjugate",
+    "quaternion_multiply",
+    "rotation_matrix_to_quaternion",
+    "get_relative_spin",
+    "get_unique_relative_spins",
+]
+
+from .array_backend import get_array_module
+from .quaternion_math import batch_quaternion_angle
+from .quaternion_utils import (
+    get_relative_spin,
+    get_unique_relative_spins,
+    is_within_angle_threshold,
+    quaternion_conjugate,
+    quaternion_distance,
+    quaternion_from_euler,
+    quaternion_multiply,
+    rotate_quaternion,
+    rotation_matrix_to_quaternion,
+)
diff --git a/spinstep/utils/array_backend.py b/spinstep/utils/array_backend.py
index cda0a84..cddace0 100644
--- a/spinstep/utils/array_backend.py
+++ b/spinstep/utils/array_backend.py
@@ -6,6 +6,8 @@
 
 from __future__ import annotations
 
+__all__ = ["get_array_module"]
+
 from types import ModuleType
 
 
diff --git a/spinstep/utils/quaternion_math.py b/spinstep/utils/quaternion_math.py
index b4c0e81..fbba4bf 100644
--- a/spinstep/utils/quaternion_math.py
+++ b/spinstep/utils/quaternion_math.py
@@ -6,10 +6,13 @@
 
 from __future__ import annotations
 
+from types import ModuleType
 from typing import Any
 
+__all__ = ["batch_quaternion_angle"]
 
-def batch_quaternion_angle(qs1: Any, qs2: Any, xp: Any) -> Any:
+
+def batch_quaternion_angle(qs1: Any, qs2: Any, xp: ModuleType) -> Any:
     """Compute pairwise angular distances between two sets of quaternions.
 
     Parameters
diff --git a/spinstep/utils/quaternion_utils.py b/spinstep/utils/quaternion_utils.py
index 81a0c92..1d711c9 100644
--- a/spinstep/utils/quaternion_utils.py
+++ b/spinstep/utils/quaternion_utils.py
@@ -6,6 +6,18 @@
 
 from __future__ import annotations
 
+__all__ = [
+    "quaternion_from_euler",
+    "quaternion_distance",
+    "rotate_quaternion",
+    "is_within_angle_threshold",
+    "quaternion_conjugate",
+    "quaternion_multiply",
+    "rotation_matrix_to_quaternion",
+    "get_relative_spin",
+    "get_unique_relative_spins",
+]
+
 from typing import List, Sequence
 
 import numpy as np