diff --git a/qim3d/utils/_doi.py b/qim3d/utils/_doi.py
index 4c3ec5f574f454fe04ab8765f52f5a703a697a27..36302e973224afad56ae2e19d7ba55b61723e310 100644
--- a/qim3d/utils/_doi.py
+++ b/qim3d/utils/_doi.py
@@ -56,7 +56,7 @@ def get_bibtex(doi):
 
     return _log_and_get_text(doi, header)
 
-def custom_header(doi, header):
+def custom_header(doi: str, header: str) -> str:
     """Allows a custom header to be passed
 
     Example:
diff --git a/qim3d/viz/_cc.py b/qim3d/viz/_cc.py
index 0bd03466b1bac36febbd533af46824f0b097a067..7b6cb2127dbb1ddc5baad4a9d6d129744a800182 100644
--- a/qim3d/viz/_cc.py
+++ b/qim3d/viz/_cc.py
@@ -23,7 +23,7 @@ def plot_cc(
         connected_components (CC): The connected components object.
         component_indexs (list | tuple, optional): The components to plot. If None the first max_cc_to_plot=32 components will be plotted. Defaults to None.
         max_cc_to_plot (int, optional): The maximum number of connected components to plot. Defaults to 32.
-        overlay (optional): Overlay image. Defaults to None.
+        overlay (np.ndarray, optional): Overlay image. Defaults to None.
         crop (bool, optional): Whether to crop the image to the cc. Defaults to False.
         display_figure (bool, optional): Whether to show the figure. Defaults to True.
         color_map (str, optional): Specifies the color map for the image. Defaults to "viridis".