diff --git a/raillabel/json_format/coordinate_system.py b/raillabel/json_format/coordinate_system.py
index 7af85e1..fbaa241 100644
--- a/raillabel/json_format/coordinate_system.py
+++ b/raillabel/json_format/coordinate_system.py
@@ -14,6 +14,14 @@ class JSONCoordinateSystem(BaseModel):
     """A 3D reference frame."""
 
     children: list[str]
+    "List of children of this coordinate system."
+
     parent: Literal["base", ""]
+    "This is the string UID of the parent coordinate system this coordinate system is referring to."
+
     pose_wrt_parent: JSONTransformData
+    "The transformation with regards to the parent coordinate system."
+
     type: Literal["sensor", "local"]
+    """This is a string that describes the type of the coordinate system, for example, 'local',
+    'geo')."""
diff --git a/raillabel/json_format/element_data_pointer.py b/raillabel/json_format/element_data_pointer.py
index 0ac6623..48cfa14 100644
--- a/raillabel/json_format/element_data_pointer.py
+++ b/raillabel/json_format/element_data_pointer.py
@@ -20,5 +20,12 @@ class JSONElementDataPointer(BaseModel):
     """
 
     attribute_pointers: dict[str, Literal["num", "text", "boolean", "vec"]]
+    """This is a JSON object which contains pointers to the attributes of the element data pointed by
+    this pointer. The attributes pointer keys shall be the 'name' of the attribute of the element
+    data this pointer points to."""
+
     frame_intervals: list[JSONFrameInterval]
+    "List of frame intervals of the element data pointed by this pointer."
+
     type: Literal["bbox", "num", "poly2d", "poly3d", "cuboid", "vec"]
+    "Type of the element data pointed by this pointer."
diff --git a/raillabel/json_format/frame_interval.py b/raillabel/json_format/frame_interval.py
index 1c5e51c..cacd837 100644
--- a/raillabel/json_format/frame_interval.py
+++ b/raillabel/json_format/frame_interval.py
@@ -13,4 +13,7 @@ class JSONFrameInterval(BaseModel):
     """
 
     start: int
+    "Initial frame number of the interval."
+
     end: int
+    "Ending frame number of the interval."
diff --git a/raillabel/json_format/transform_data.py b/raillabel/json_format/transform_data.py
index b86f9f0..edf7c87 100644
--- a/raillabel/json_format/transform_data.py
+++ b/raillabel/json_format/transform_data.py
@@ -10,4 +10,7 @@ class JSONTransformData(BaseModel):
     """The translation and rotation of one coordinate system to another."""
 
     translation: tuple[float, float, float]
+    "List of 4 values encoding a quaternion (x, y, z, w)."
+
     quaternion: tuple[float, float, float, float]
+    "List of 3 values encoding the translation vector (x, y, z)"