diff --git a/idc_index/index.py b/idc_index/index.py
index 2efea596..fe7fc952 100644
--- a/idc_index/index.py
+++ b/idc_index/index.py
@@ -100,19 +100,54 @@ def _filter_by_dicom_series_uid(df_index, dicom_series_uid):
 
     @staticmethod
     def get_idc_version():
+        """
+        Returns the version of IDC data used in idc-index
+        """
         return f"v{idc_index_data.__version__}"
 
     def get_collections(self):
+        """
+        Returns the collections present in IDC
+        """
         unique_collections = self.index["collection_id"].unique()
         return unique_collections.tolist()
 
     def get_series_size(self, seriesInstanceUID):
+        """
+        Gets cumulative size (MB) of the DICOM instances in a given SeriesInstanceUID.
+
+        Args:
+            seriesInstanceUID (str): The DICOM SeriesInstanceUID.
+
+        Returns:
+            float: The cumulative size of the DICOM instances in the given SeriesInstanceUID rounded to two digits, in MB.
+
+        Raises:
+            ValueError: If the `seriesInstanceUID` does not exist.
+        """
+
         resp = self.index[["SeriesInstanceUID"] == seriesInstanceUID][
             "series_size_MB"
         ].iloc[0]
         return resp
 
     def get_patients(self, collection_id, outputFormat="dict"):
+        """
+        Gets the patients in a collection.
+
+        Args:
+            collection_id (str or a list of str): The collection id or list of collection ids. This should be in lower case separated by underscores.
+                                For example, 'pdmr_texture_analysis'. or ['pdmr_texture_analysis','nlst']
+            outputFormat (str, optional): The format in which to return the patient IDs. Available options are 'dict',
+                                        'df', and 'list'. Default is 'dict'.
+
+        Returns:
+            dict or pandas.DataFrame or list: Patient IDs in the requested output format. By default, it returns a dictionary.
+
+        Raises:
+            ValueError: If `outputFormat` is not one of 'dict', 'df', 'list'.
+        """
+
         if not isinstance(collection_id, str) and not isinstance(collection_id, list):
             raise TypeError("collection_id must be a string or list of strings")
 
@@ -149,7 +184,21 @@ def get_patients(self, collection_id, outputFormat="dict"):
         return response
 
     def get_dicom_studies(self, patientId, outputFormat="dict"):
-        """returns one row per distinct value of StudyInstanceUID"""
+        """
+        Returns Studies for a given patient or list of patients.
+
+        Args:
+            patientId (str or list of str): The patient Id or a list of patient Ids.
+            outputFormat (str, optional): The format in which to return the studies. Available options are 'dict',
+                                        'df', and 'list'. Default is 'dict'.
+
+        Returns:
+            dict or pandas.DataFrame or list: Studies in the requested output format. By default, it returns a dictionary.
+
+        Raises:
+            ValueError: If `outputFormat` is not one of 'dict', 'df', 'list'.
+            ValueError: If any of the `patientId` does not exist.
+        """
 
         if not isinstance(patientId, str) and not isinstance(patientId, list):
             raise TypeError("patientId must be a string or list of strings")
@@ -211,7 +260,23 @@ def get_dicom_studies(self, patientId, outputFormat="dict"):
 
         return response
 
-    def get_dicom_series(self, studyInstanceUID=None, outputFormat="dict"):
+    def get_dicom_series(self, studyInstanceUID, outputFormat="dict"):
+        """
+        Returns Series for a given study or list of studies.
+
+        Args:
+            studyInstanceUID (str or list of str): The DICOM StudyInstanceUID or a list of StudyInstanceUIDs.
+            outputFormat (str, optional): The format in which to return the series. Available options are 'dict',
+                                        'df', and 'list'. Default is 'dict'.
+
+        Returns:
+            dict or pandas.DataFrame or list: Series in the requested output format. By default, it returns a dictionary.
+
+        Raises:
+            ValueError: If `outputFormat` is not one of 'dict', 'df', 'list'.
+            ValueError: If any of the `studyInstanceUID` does not exist.
+        """
+
         if not isinstance(studyInstanceUID, str) and not isinstance(
             studyInstanceUID, list
         ):
@@ -357,7 +422,7 @@ def get_series_file_URLs(self, seriesInstanceUID):
         return file_names
 
     def get_viewer_URL(
-        self, seriesInstanceUID, studyInstanceUID=None, viewer_selector=None
+        self, seriesInstanceUID=None, studyInstanceUID=None, viewer_selector=None
     ):
         """
         Get the URL of the IDC viewer for the given series or study in IDC based on
@@ -376,7 +441,7 @@ def get_viewer_URL(
             available in IDC
 
             viewer_selector: string containing the name of the viewer to use. Must be one of the following:
-            ohif_v2, ohif_v2, or slim. If not provided, default viewers will be used.
+            ohif_v2, ohif_v3, or slim. If not provided, default viewers will be used.
 
         Returns:
             string containing the IDC viewer URL for the given SeriesInstanceUID
@@ -387,7 +452,10 @@ def get_viewer_URL(
                 "Either SeriesInstanceUID or StudyInstanceUID, or both, must be provided."
             )
 
-        if seriesInstanceUID not in self.index["SeriesInstanceUID"].values:
+        if (
+            seriesInstanceUID is not None
+            and seriesInstanceUID not in self.index["SeriesInstanceUID"].values
+        ):
             raise ValueError("SeriesInstanceUID not found in IDC index.")
 
         if (