diff --git a/day18/__init__.py b/day18/__init__.py
index e69de29..b978876 100644
--- a/day18/__init__.py
+++ b/day18/__init__.py
@@ -0,0 +1 @@
+"""Day18 solution."""
diff --git a/day18/day18a.py b/day18/day18a.py
index 895b6a8..b91fcd5 100644
--- a/day18/day18a.py
+++ b/day18/day18a.py
@@ -1,4 +1,4 @@
-"""day18 solution"""
+"""day18 solution."""
 
 from dataclasses import dataclass
 from enum import StrEnum
@@ -12,25 +12,33 @@
 
 @dataclass
 class Position:
+    """Simple 2d point."""
+
     row: int = 0
     col: int = 0
 
 
 class Direction(StrEnum):
+    """Cardinal direction in ``UDLR``."""
+
     Up = "U"
     Down = "D"
     Left = "L"
     Right = "R"
 
     def __repr__(self) -> str:  # pragma: no cover
+        """Custom repr for easy printing."""
         return str(self)
 
     def __str__(self) -> str:
+        """Up/Down/Left/Right."""
         return self.name
 
 
-@dataclass
+@dataclass(frozen=True)
 class Command:
+    """Well defined command dataclass."""
+
     direction: Direction
     steps: int
     color: str
@@ -39,6 +47,19 @@ class Command:
 def generate_offsets(
     position: Position, direction: Direction, steps: int
 ) -> list[Position]:
+    """Generate position offsets.
+
+    Args:
+        position (Position): base position
+        direction (Direction): direction of travel
+        steps (int): number of steps to generate
+
+    Raises:
+        AssertionError: If direciton is invalid.
+
+    Returns:
+        list[Position]: list of new positions.
+    """
     if direction == Direction.Right:
         return [Position(position.row, position.col + i) for i in range(1, steps + 1)]
     if direction == Direction.Left:
@@ -51,6 +72,8 @@ def generate_offsets(
 
 
 class Matrix:
+    """2d array representing world."""
+
     contents: list[list[Tile]]
 
     min_pos: Position
@@ -63,6 +86,7 @@ class Matrix:
     dug_tiles = 0
 
     def __init__(self, min_pos: Position, max_pos: Position) -> None:
+        """Generate 2d array with min/max position for offsetting."""
         self.num_rows = max_pos.row - min_pos.row + 1
         self.num_cols = max_pos.col - min_pos.col + 1
         self.contents = [
@@ -70,7 +94,17 @@ def __init__(self, min_pos: Position, max_pos: Position) -> None:
         ]
 
     def process_command(self, miner_pos: Position, command: Command) -> Position:
-        """Process command, returning miner's new position"""
+        """Process command.
+
+        This moves the miner around.
+
+        Args:
+            miner_pos (Position): miner's current position
+            command (Command): command to process
+
+        Returns:
+            Position: miner's new position.
+        """
         offsets = generate_offsets(miner_pos, command.direction, command.steps)
         self.wall_tiles += len(offsets)
         for offset in offsets:
@@ -78,8 +112,7 @@ def process_command(self, miner_pos: Position, command: Command) -> Position:
         return offsets[-1]
 
     def dig_out(self) -> None:
-        # digs out the non-perimeter tiles, returning how many were "dug out"
-
+        """Dig out non-perimeter tiles using flood-fill."""
         # cache for what's been visited
         visited: list[list[bool]] = [
             [False for _ in range(self.num_cols)] for _ in range(self.num_rows)
@@ -105,7 +138,14 @@ def dig_out(self) -> None:
                 to_process.put(generate_offsets(position, direction, 1)[0])
 
     def is_oob(self, position: Position) -> bool:
-        """True if position out of bounds"""
+        """Returns if a position is out of bounds.
+
+        Args:
+            position (Position): position to check.
+
+        Returns:
+            bool: True if out of bounds.
+        """
         return (
             position.row < 0
             or position.row >= self.num_rows
@@ -114,10 +154,22 @@ def is_oob(self, position: Position) -> bool:
         )
 
     def __str__(self) -> str:
+        """Custom __str__ for pretty printing matrix."""
         return "\n".join("".join(str(tile) for tile in row) for row in self.contents)
 
 
 def get_matrix_range(commands: list[Command]) -> tuple[Position, Position]:
+    """Calculate minimum and maximum position in matrix.
+
+    Since we start in the middle somewhere, we get negative positions.
+    This can be useds to offset the matrix when we construct it.
+
+    Args:
+        commands (list[Command]): list of commands that will be run.
+
+    Returns:
+        tuple[Position, Position]: [min,max] positions.
+    """
     position = Position()
     max_row, max_col = 0, 0
     min_row, min_col = 0, 0
@@ -131,6 +183,7 @@ def get_matrix_range(commands: list[Command]) -> tuple[Position, Position]:
 
 
 def get_input(path: str) -> list[Command]:
+    """Reads input from file into well-formed list of commands."""
     commands = []
     with open(path, encoding="utf-8") as file:
         for line in file:
@@ -141,6 +194,13 @@ def get_input(path: str) -> list[Command]:
 
 
 def get_solution(commands: list[Command]) -> int:
+    """Calculates solution.
+
+    1. Pre-calculates the range
+    2. Creates edge tiles
+    3. Flood fill centre.
+    4. Count tiles.
+    """
     min_pos, max_pos = get_matrix_range(commands)
 
     matrix: Matrix = Matrix(min_pos, max_pos)
@@ -159,6 +219,7 @@ def get_solution(commands: list[Command]) -> int:
 
 
 def main() -> None:
+    """Load data and then find solution to part1."""
     commands: list[Command] = get_input(INPUT)
     get_solution(commands)
 
diff --git a/day18/day18b.py b/day18/day18b.py
index 0c0a629..cc362b7 100644
--- a/day18/day18b.py
+++ b/day18/day18b.py
@@ -1,3 +1,4 @@
+"""Day18b solution."""
 from dataclasses import dataclass
 from enum import IntEnum
 
@@ -7,11 +8,15 @@
 
 @dataclass
 class Position:
+    """Simple 2d vector."""
+
     row: int = 0
     col: int = 0
 
 
 class Direction(IntEnum):
+    """Direction as an integer enum."""
+
     Right = 0
     Down = 1
     Left = 2
@@ -20,15 +25,19 @@ class Direction(IntEnum):
 
 @dataclass(init=False)
 class Command:
+    """Command from hexstring."""
+
     direction: Direction
     steps: int
 
     def __init__(self, hexcode: str):
+        """Converts from hexcode to well formed direction+steps."""
         self.steps = int(hexcode[:5], 16)
         self.direction = Direction(int(hexcode[-1]))
 
 
 def get_input(path: str) -> list[Command]:
+    """Grabs input from file, parsing into well-formed commands."""
     commands = []
     with open(path, encoding="utf-8") as file:
         for line in file:
@@ -39,6 +48,7 @@ def get_input(path: str) -> list[Command]:
 
 
 def process_command(command: Command, position: Position) -> Position:
+    """Process a command and return new position."""
     if command.direction == Direction.Right:
         return Position(position.row, position.col + command.steps)
     if command.direction == Direction.Down:
@@ -51,6 +61,7 @@ def process_command(command: Command, position: Position) -> Position:
 
 
 def calculate_area(positions: list[Position], perimeter: int) -> int:
+    """Calculate area using shoelace area."""
     # total_area = shoelace_area + (perimeter_length // 2) + 1
 
     # shoelace assumes that each point is in centre, but each
@@ -67,6 +78,7 @@ def calculate_area(positions: list[Position], perimeter: int) -> int:
 
 
 def get_solution(commands: list[Command]) -> int:
+    """Get solution via processing commands then running shoelace area."""
     positions: list[Position] = []
     position = Position()
 
@@ -80,6 +92,7 @@ def get_solution(commands: list[Command]) -> int:
 
 
 def main() -> None:
+    """Grab input and then pass it into solver."""
     commands: list[Command] = get_input(INPUT)
 
     print(get_solution(commands))
diff --git a/day18/lib/__init__.py b/day18/lib/__init__.py
index e69de29..dca6b0a 100644
--- a/day18/lib/__init__.py
+++ b/day18/lib/__init__.py
@@ -0,0 +1 @@
+"""day18 library modules."""
diff --git a/day18/lib/tile.py b/day18/lib/tile.py
index bfde4d5..4bdd5d6 100644
--- a/day18/lib/tile.py
+++ b/day18/lib/tile.py
@@ -1,16 +1,22 @@
+"""Tile Class."""
 from dataclasses import dataclass
 
 
 @dataclass
 class Tile:
+    """Tile for part 1, represents a non-dugout tile."""
+
     contents: str = "."
 
     def __str__(self) -> str:
+        """Custom str for easy printing."""
         return self.contents
 
 
 @dataclass(kw_only=True)
 class EdgeTile(Tile):
+    """Edge tile (``#``)."""
+
     contents: str = "#"
     color: str
 
@@ -18,9 +24,11 @@ class EdgeTile(Tile):
     TEXT_WHITE = "\033[38;2;255;255;255m"
 
     def text_color(self, r: int, g: int, b: int) -> str:
+        """Return ansicode color of edge based on input."""
         return f"\033[38;2;{r};{g};{b}m"
 
     def __str__(self) -> str:
+        """Return colored string of ``#`` based on hexcode."""
         r, g, b = [int(self.color[i * 2 : i * 2 + 2], 16) for i in range(3)]
 
         return f"{self.text_color(r,g,b)}{self.contents}{self.TEXT_WHITE}"
@@ -28,4 +36,6 @@ def __str__(self) -> str:
 
 @dataclass(kw_only=True)
 class HoleTile(Tile):
+    """Dug out tile."""
+
     contents: str = " "
diff --git a/day18/tests/__init__.py b/day18/tests/__init__.py
index e69de29..b441fe2 100644
--- a/day18/tests/__init__.py
+++ b/day18/tests/__init__.py
@@ -0,0 +1 @@
+"""day18 tests."""
diff --git a/day18/tests/test_day18a.py b/day18/tests/test_day18a.py
index f264471..1e1e073 100644
--- a/day18/tests/test_day18a.py
+++ b/day18/tests/test_day18a.py
@@ -1,7 +1,9 @@
+"""test day18a main function."""
 from day18.day18a import INPUT_SMALL, Command, Direction, get_input, get_solution
 
 
 def test_day18a() -> None:
+    """Test day18a."""
     commands: list[Command] = get_input(INPUT_SMALL)
     assert len(commands) == 14
     assert commands[0].steps == 6 and commands[0].direction == Direction.Right
diff --git a/day18/tests/test_day18b.py b/day18/tests/test_day18b.py
index 784f056..4003bbe 100644
--- a/day18/tests/test_day18b.py
+++ b/day18/tests/test_day18b.py
@@ -1,7 +1,9 @@
+"""test day18b main functions."""
 from day18.day18b import INPUT_SMALL, Command, Direction, get_input, get_solution
 
 
 def test_day18b() -> None:
+    """Test day18b main function."""
     commands: list[Command] = get_input(INPUT_SMALL)
     assert len(commands) == 14
     assert commands[0].steps == 461937 and commands[0].direction == Direction.Right
@@ -11,6 +13,7 @@ def test_day18b() -> None:
 
 
 def test_command() -> None:
+    """Test hex code conversion."""
     assert Command("70c710").steps == 461937
     assert Command("0dc571").steps == 56407
     assert Command("5713f0").steps == 356671