diff --git a/chatgpt_pyapi/__init__.py b/chatgpt_pyapi/__init__.py
index 9f80222..566d26f 100644
--- a/chatgpt_pyapi/__init__.py
+++ b/chatgpt_pyapi/__init__.py
@@ -21,15 +21,20 @@ class Message:
     '''Message type. Supports roles.'''
 
     def __init__(self, text: str, role: str = Roles.USER):
+        assert type(text) == str
+        assert type(role) == str
         self.text = text
         self.role = role
 
     @classmethod
-    def from_api(cls, message_dict:str):
+    def from_api(cls, api_msg: dict):
         '''Create a Message object from API format'''
+        assert type(api_msg) == dict
+        msg = api_msg["choices"][0]["message"]
+        msg["content"] = msg["content"].strip("\n")
         return cls(
-            message_dict["content"],
-            message_dict["role"])
+            msg["content"],
+            msg["role"])
 
     def to_api(self):
         '''Convert to API format'''
@@ -42,6 +47,8 @@ class ChatGPT:
     API_ENDPOINT = "https://api.openai.com/v1/chat/completions"
 
     def __init__(self, api_key: str, model: str = Models.GPT_35_TURBO):
+        assert type(api_key) == str
+        assert type(model) == str
         # Create string used in header
         self.auth = f"Bearer {api_key}"
         # This list will contain all prior messages
@@ -51,12 +58,12 @@ class ChatGPT:
     def chat(self, message: Message) -> Message:
         '''Add a message to the message history & send it to ChatGPT. Returns the answer as a Message instance.'''
         self.add_to_chat(message)
-        # create api_input from message_history & encode it
+        # Create api_input from message_history & encode it
         api_input = [m.to_api() for m in self._message_history]
         api_input_encoded = dumps(
             {"model": self.model, "messages": api_input},
             separators=(",", ":")).encode()
-        # create a Request object with the right url, data, headers and http method
+        # Create a Request object with the right url, data, headers and http method
         request = http_request.Request(
             self.API_ENDPOINT,
             data=api_input_encoded,
@@ -65,21 +72,18 @@ class ChatGPT:
                 "Content-Type": "application/json"
             },
             method="POST")
-        # send the request with r as the response
+        # Send the request with r as the response
         with http_request.urlopen(request) as r:
-            # read response and parse json
+            # Read response and parse json
             api_output = loads(r.read())
-            api_output_answer = api_output["choices"][0]["message"]
-            # remove leading and trailing newlines
-            api_output_answer["content"] = api_output_answer["content"].strip("\n")
-            # convert to Message object
-            response_message = Message.from_api(api_output_answer)
+            # Convert to Message object
+            response_message = Message.from_api(api_output)
             self._message_history.append(response_message)
             return response_message
 
     def add_to_chat(self, message: Message) -> Message:
         '''Add a message to the message history without sending it to ChatGPT'''
-        # check if the message parameter is the correct type
+        # Check if the message parameter is the correct type
         assert type(message) == Message, "message must be an instance of Message"
         self._message_history.append(message)