diff --git a/shenzhen_solitaire/board_actions.py b/shenzhen_solitaire/board_actions.py
index 2056fca..d9e49bb 100644
--- a/shenzhen_solitaire/board_actions.py
+++ b/shenzhen_solitaire/board_actions.py
@@ -5,6 +5,7 @@ from . import board
 
 
 class Action:
+    """Base class for a card move action on a solitaire board"""
     _before_state: int = 0
     _after_state: int = 0
 
@@ -15,6 +16,7 @@ class Action:
         pass
 
     def apply(self, action_board: board.Board) -> None:
+        """Apply action to board"""
         if __debug__:
             self._before_state = action_board.state_identifier
         self._apply(action_board)
@@ -22,6 +24,7 @@ class Action:
             self._after_state = action_board.state_identifier
 
     def undo(self, action_board: board.Board) -> None:
+        """Undo action to board"""
         assert action_board.state_identifier == self._after_state
         self._undo(action_board)
         assert action_board.state_identifier == self._before_state
diff --git a/shenzhen_solitaire/solver.py b/shenzhen_solitaire/solver.py
index f1eda01..2beffb7 100644
--- a/shenzhen_solitaire/solver.py
+++ b/shenzhen_solitaire/solver.py
@@ -11,6 +11,7 @@ from .board_actions import (
 
 
 class ActionStack:
+    """Stack of chosen actions on the board"""
     iterator_stack: List[Iterator[board_actions.Action]]
     action_stack: List[Optional[board_actions.Action]]
     index_stack: List[int]
@@ -23,12 +24,14 @@ class ActionStack:
         self.state_stack = []
 
     def push(self, board: Board) -> None:
+        """Append another board state to stack"""
         self.iterator_stack.append(possible_actions(board))
         self.action_stack.append(None)
         self.index_stack.append(0)
         self.state_stack.append(board.state_identifier)
 
     def get(self) -> Optional[board_actions.Action]:
+        """Get next iteration of top action iterator"""
         try:
             self.action_stack[-1] = next(self.iterator_stack[-1])
         except StopIteration:
@@ -37,6 +40,7 @@ class ActionStack:
         return self.action_stack[-1]
 
     def pop(self) -> None:
+        """Pop one action from stack"""
         self.action_stack.pop()
         self.iterator_stack.pop()
         self.index_stack.pop()