diff --git a/src/wireviz/Harness.py b/src/wireviz/Harness.py
index ca9f8e6..95e7a2a 100644
--- a/src/wireviz/Harness.py
+++ b/src/wireviz/Harness.py
@@ -20,16 +20,16 @@ class Harness:
         self.cables = {}
         self.additional_bom_items = []
 
-    def add_connector(self, name, *args, **kwargs):
+    def add_connector(self, name: str, *args, **kwargs) -> None:
         self.connectors[name] = Connector(name, *args, **kwargs)
 
-    def add_cable(self, name, *args, **kwargs):
+    def add_cable(self, name: str, *args, **kwargs) -> None:
         self.cables[name] = Cable(name, *args, **kwargs)
 
-    def add_bom_item(self, item):
+    def add_bom_item(self, item: dict) -> None:
         self.additional_bom_items.append(item)
 
-    def connect(self, from_name, from_pin, via_name, via_pin, to_name, to_pin):
+    def connect(self, from_name: str, from_pin: (int, str), via_name: str, via_pin: (int, str), to_name: str, to_pin: (int, str)) -> None:
         for (name, pin) in zip([from_name, to_name], [from_pin, to_pin]):  # check from and to connectors
             if name is not None and name in self.connectors:
                 connector = self.connectors[name]
@@ -58,7 +58,7 @@ class Harness:
         if to_name in self.connectors:
             self.connectors[to_name].activate_pin(to_pin)
 
-    def create_graph(self):
+    def create_graph(self) -> Graph:
         dot = Graph()
         dot.body.append('// Graph generated by WireViz')
         dot.body.append('// https://github.com/formatc1702/WireViz')
@@ -280,7 +280,7 @@ class Harness:
         data.seek(0)
         return data.read()
 
-    def output(self, filename: (str, Path), view=False, cleanup=True, fmt=('pdf', )):
+    def output(self, filename: (str, Path), view: bool = False, cleanup: bool = True, fmt: tuple = ('pdf', )) -> None:
         # graphical output
         graph = self.create_graph()
         for f in fmt:
diff --git a/src/wireviz/wireviz.py b/src/wireviz/wireviz.py
index d52d3b1..6c9a186 100755
--- a/src/wireviz/wireviz.py
+++ b/src/wireviz/wireviz.py
@@ -3,8 +3,9 @@
 
 import argparse
 import os
+from pathlib import Path
 import sys
-from typing import Tuple
+from typing import Any, Tuple
 
 import yaml
 
@@ -16,7 +17,7 @@ from wireviz.Harness import Harness
 from wireviz.wv_helper import expand
 
 
-def parse(yaml_input, file_out=None, return_types: (None, str, Tuple[str]) = None):
+def parse(yaml_input: str, file_out: (str, Path) = None, return_types: (None, str, Tuple[str]) = None) -> Any:
     """
     Parses yaml input string and does the high-level harness conversion
 
@@ -196,7 +197,7 @@ def parse(yaml_input, file_out=None, return_types: (None, str, Tuple[str]) = Non
         return tuple(returns) if len(returns) != 1 else returns[0]
 
 
-def parse_file(yaml_file, file_out=None):
+def parse_file(yaml_file: str, file_out: (str, Path) = None) -> None:
     with open(yaml_file, 'r') as file:
         yaml_input = file.read()