diff --git a/google/api_handler.py b/google/api_handler.py
index f2aed65..074c1a2 100644
--- a/google/api_handler.py
+++ b/google/api_handler.py
@@ -1,4 +1,4 @@
-# Copyright 2019-2020 cj-wong
+# Copyright 2019-2021 cj-wong
 # Copyright 2018 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -37,13 +37,17 @@
 
 class ExpiredCredentials(RuntimeError):
     """Credentials were expired."""
+
     def __init__(self):
+        """Initialize the error with a message."""
         super().__init__('Credentials expired')
 
 
 def authorize() -> service_account.Credentials:
-    """Adapted from Google's example:
-    https://developers.google.com/calendar/quickstart/python
+    """Authorize the connection to the Google API.
+
+    Adapted from Google's example:
+        https://developers.google.com/calendar/quickstart/python
 
     See NOTICE for attribution.
 
diff --git a/google/calendar.py b/google/calendar.py
index 22a9d58..b8ae270 100644
--- a/google/calendar.py
+++ b/google/calendar.py
@@ -1,4 +1,4 @@
-# Copyright 2019-2020 cj-wong
+# Copyright 2019-2021 cj-wong
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -25,7 +25,7 @@
 
 
 def get_tab(entry: str) -> Union[str, None]:
-    """Gets a tab given an `entry`, if it exists in `config.TAB_NAMES`.
+    """Get a tab given its name, if it exists in `config.TAB_NAMES`.
 
     Args:
         entry (str): the name of an entry
@@ -47,22 +47,24 @@ def get_tab(entry: str) -> Union[str, None]:
 
 class TabNotFound(ValueError):
     """The tab name wasn't found in the configuration. Ignore it."""
+
     pass
 
 
 class Calendar:
-    """Class for managing calendar.
+    """Class for managing Google Calendar.
 
     Attributes:
         interface (Resource): an interface created from credentials;
             used to retrieve calendars and entries per calendar
 
     """
+
     def __init__(self, credentials: service_account.Credentials) -> None:
-        """Initialize the Calendar interface.
+        """Initialize the Google Calendar interface.
 
         Args:
-            credentials (service_account.Credentials): for Google APIs
+            credentials (service_account.Credentials): creds for Google APIs
 
         """
         self.interface = build(
@@ -72,8 +74,9 @@ def __init__(self, credentials: service_account.Credentials) -> None:
             )
 
     def get_calendar_ids(self) -> Dict[str, str]:
-        """Gets IDs for calendars configured in config.yaml. They will
-        be used for retrieving entries/events per calendar.
+        """Get IDs for calendars configured in config.yaml.
+
+        The IDs will be used for retrieving entries/events per calendar.
 
         Returns:
             Dict[str, str]: {calendar name: calendar id}
@@ -91,9 +94,9 @@ def get_calendar_ids(self) -> Dict[str, str]:
         return cals
 
     def get_entries(self, cal_name: str, cal_id: str) -> Dict[str, int]:
-        """Gets entries in a calendar given `cal_id` from yesterday
-        until today. We are interested in events that have elapsed
-        from then and now.
+        """Get entries in a calendar given `cal_id` from yesterday until today.
+
+        We are interested in events that have elapsed from then and now.
 
         Args:
             cal_name (str): the name (summary) of the calendar
diff --git a/google/sheets.py b/google/sheets.py
index bdc06e0..f361b2e 100644
--- a/google/sheets.py
+++ b/google/sheets.py
@@ -1,4 +1,4 @@
-# Copyright 2019-2020 cj-wong
+# Copyright 2019-2021 cj-wong
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -27,11 +27,11 @@
 
 
 def get_yesterday_cell(start: Dict[str, Union[str, int]]) -> str:
-    """Retrieve the cell representing yesterday, given the starting
-    cell and its characteristics. Note that if the cell isn't valid,
-    `AttributeError` ,`TypeError`, or `ValueError` may be raised,
-    from attempted string slicing (e.g. `cell[:col_end]`) and type-casts
-    (e.g. `int(cell[col_end:])`).
+    """Retrieve the cell location representing yesterday.
+
+    The cell location can be determined given the starting cell location and
+    year and month offsets. Note that if the cell isn't valid, AttributeError
+    or TypeError may be raised, albeit indirectly.
 
     Args:
         start (Dict[str, Union[str, int]]): the characteristics of
@@ -41,6 +41,10 @@ def get_yesterday_cell(start: Dict[str, Union[str, int]]) -> str:
     Returns:
         str: the cell in spreadsheet format, e.g. 'A1'
 
+    Raises:
+        AttributeError: if any intermediary values are None
+        TypeError: slicing or casting on None
+
     """
     cell = start['cell']
     first = pendulum.datetime(start['year'], start['month'], 1, tz='local')
@@ -64,13 +68,14 @@ def get_yesterday_cell(start: Dict[str, Union[str, int]]) -> str:
 
 
 class Sheets:
-    """Class for manging sheets.
+    """Class for Google Sheets.
 
     Attributes:
         interface (Resource): an interface created from credentials;
             used to retrieve spreadsheets and their sheets
 
     """
+
     def __init__(self, credentials) -> None:
         """Initialize the Sheets interface.
 
@@ -85,8 +90,9 @@ def __init__(self, credentials) -> None:
             ).spreadsheets()
 
     def get_tab_cells(self) -> Dict[str, str]:
-        """For all valid tabs, get the cell representing yesterday so
-        the hours can be recorded there.
+        """Get the cell representing yesterday to be written with hours.
+
+        If the cell is invalid, nothing will be written.
 
         Returns:
             Dict[str, str]: {tab name: syntax for yesterday's cell}
@@ -108,13 +114,12 @@ def get_tab_cells(self) -> Dict[str, str]:
         return tab_cells
 
     def input_hours(self, tab_hours: Dict[str, int]) -> None:
-        """Inputs hours given `tab_hours` into their respective sheets.
+        """Input hours into their respective sheets.
 
         Args:
             tab_hours (Dict[str, int]): {tab name: hours}
 
         """
-
         values = self.interface.values()
 
         tab_cells = self.get_tab_cells()
diff --git a/main.py b/main.py
index 12889e9..f1b946e 100644
--- a/main.py
+++ b/main.py
@@ -1,4 +1,4 @@
-# Copyright 2019-2020 cj-wong
+# Copyright 2019-2021 cj-wong
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -22,8 +22,9 @@
 
 
 def main() -> None:
-    """This function runs everything: authorizes the connection,
-    reads calendars, and writes to spreadsheet if records were found.
+    """Run everything: authorization, calendar reads, spreadsheet writes.
+
+    The spreadsheet is only written if events in the calendar are found.
 
     """
     creds = google.api_handler.authorize()
@@ -32,8 +33,7 @@ def main() -> None:
     calendars = calendar_api.get_calendar_ids()
     if not calendars:
         LOGGER.error(
-            'No calendars were found matching any in your configuration'
-            )
+            'No calendars were found matching any in your configuration')
         return
     for cal_name, cal_id in calendars.items():
         tab_hours = calendar_api.get_entries(cal_name, cal_id)