diff --git a/t4_devkit/helper/rendering.py b/t4_devkit/helper/rendering.py
index 1c748078..938269a4 100644
--- a/t4_devkit/helper/rendering.py
+++ b/t4_devkit/helper/rendering.py
@@ -41,6 +41,8 @@
 
 
 class RenderingMode(Enum):
+    """Rendering mode enumerations."""
+
     SCENE = "scene"
     INSTANCE = "instance"
     POINTCLOUD = "pointcloud"
@@ -66,9 +68,11 @@ def __init__(self, t4: Tier4) -> None:
         self._executor = concurrent.futures.ThreadPoolExecutor()
 
     def _has_lidarseg(self) -> bool:
+        """Return `True` if the dataset includes lidarseg."""
         return bool(self._sample_data_to_lidarseg_filename)
 
     def _find_lidarseg_file(self, sample_data_token: str) -> str | None:
+        """Try to find lidarseg filename from the sample data token."""
         return self._sample_data_to_lidarseg_filename.get(sample_data_token)
 
     def _init_viewer(
diff --git a/t4_devkit/viewer/builder.py b/t4_devkit/viewer/builder.py
index bb27eec8..e33b6ddd 100644
--- a/t4_devkit/viewer/builder.py
+++ b/t4_devkit/viewer/builder.py
@@ -33,10 +33,24 @@ def __init__(self) -> None:
         self._config = ViewerConfig()
 
     def with_spatial3d(self) -> Self:
+        """Update the viewer configuration to include 3D view space.
+
+        Returns:
+            Self: Updated `ViewerBuilder` instance itself.
+        """
         self._config.spatial3ds.append(rrb.Spatial3DView(name="3D", origin=EntityPath.MAP))
         return self
 
     def with_spatial2d(self, cameras: Sequence[str], contents: list[str] | None = None) -> Self:
+        """Update the viewer configuration to include 2D view spaces for each camera.
+
+        Args:
+            cameras (Sequence[str]): Camera names.
+            contents (list[str] | None): List of 3D view contents to project onto 2D view spaces.
+
+        Returns:
+            Self: Updated `ViewerBuilder` instance itself.
+        """
         # Preserve the original contents arguments so each camera gets its own view_contents.
         base_contents = contents
         for name in cameras:
@@ -53,14 +67,39 @@ def with_spatial2d(self, cameras: Sequence[str], contents: list[str] | None = No
         return self
 
     def with_labels(self, label2id: dict[str, int]) -> Self:
+        """Update the viewer configuration to include label to id mapping.
+
+        Args:
+            label2id (dict[str, int]): Key-value mapping to convert label name to its ID.
+
+        Returns:
+            Self: Updated `ViewerBuilder` instance itself.
+        """
         self._config.label2id = label2id
         return self
 
     def with_streetmap(self, latlon: Vector2Like | None = None) -> Self:
+        """Update the viewer configuration to include the streetmap view space.
+
+        Args:
+            latlon (Vector2Like | None): Starting point in (latitude, longitude).
+
+        Returns:
+            Self: Updated `ViewerBuilder` instance itself.
+        """
         self._config.spatial3ds.append(rrb.MapView(name="Map", origin=EntityPath.GEOCOORDINATE))
         if latlon is not None:
             self._config.latlon = latlon
         return self
 
     def build(self, app_id: str, save_dir: str | None = None) -> RerunViewer:
+        """Build `RerunViewer` from the configuration.
+
+        Args:
+            app_id (str): Viewer application ID.
+            save_dir (str | None): Directory path to save the rendering record.
+
+        Returns:
+            RerunViewer: Viewer instance.
+        """
         return RerunViewer(app_id=app_id, config=self._config, save_dir=save_dir)
diff --git a/t4_devkit/viewer/color.py b/t4_devkit/viewer/color.py
index 435abc38..fb465f8f 100644
--- a/t4_devkit/viewer/color.py
+++ b/t4_devkit/viewer/color.py
@@ -32,6 +32,9 @@ def pointcloud_color(
     Args:
         pointcloud (PointCloudLike): Any inheritance of `PointCloud` class.
         color_mode (PointCloudColorMode, optional): Color mode for pointcloud.
+
+    Returns:
+        NDArrayF64: RGB color array in the shape of (N, 3).
     """
     match color_mode:
         case PointCloudColorMode.DISTANCE:
diff --git a/t4_devkit/viewer/config.py b/t4_devkit/viewer/config.py
index 5c15d344..1c894b20 100644
--- a/t4_devkit/viewer/config.py
+++ b/t4_devkit/viewer/config.py
@@ -30,6 +30,15 @@ class EntityPath(str, Enum):
 
 @define
 class ViewerConfig:
+    """Viewer configuration.
+
+    Attributes:
+        spatial3ds (list[rrb.Spatial3DView | rrb.MapView]): List of 3D spatial views.
+        spatial2ds (list[rrb.Spatial2DView]): List of 2D spatial views.
+        label2id (dict[str, int]): Key-value mapping to convert label name to its ID.
+        latlon (Vector2Like | None): Starting point in (latitude, longitude).
+    """
+
     spatial3ds: list[rrb.Spatial3DView | rrb.MapView] = field(factory=list)
     spatial2ds: list[rrb.Spatial2DView] = field(factory=list)
     label2id: dict[str, int] = field(factory=dict)