diff --git a/src/openai_messages_token_helper/message_builder.py b/src/openai_messages_token_helper/message_builder.py
index 86203de..790b1cd 100644
--- a/src/openai_messages_token_helper/message_builder.py
+++ b/src/openai_messages_token_helper/message_builder.py
@@ -147,8 +147,12 @@ def build_messages(
             logging.info("Reached max tokens of %d, history will be truncated", max_tokens)
             break
 
-        if message["role"] is None or message["content"] is None:
-            raise ValueError("Few-shot messages must have both role and content")
-        message_builder.insert_message(message["role"], message["content"], index=append_index)  # type: ignore[arg-type]
+        if message["role"] is None or (message["content"] is None and message.get("role") != "assistant"):
+            raise ValueError("Past messages must have both role and content, unless it is a tools message from assistant.")
+
+        message_builder.insert_message(message["role"], message["content"], 
+                                       tool_calls=message.get("tool_calls",None), 
+                                       tool_call_id=message.get("tool_call_id",None),
+                                       index=append_index)  # type: ignore[arg-type]
         total_token_count += potential_message_count
     return message_builder.all_messages
diff --git a/src/openai_messages_token_helper/model_helper.py b/src/openai_messages_token_helper/model_helper.py
index 1d131a1..ff96612 100644
--- a/src/openai_messages_token_helper/model_helper.py
+++ b/src/openai_messages_token_helper/model_helper.py
@@ -91,7 +91,7 @@ def count_tokens_for_message(model: str, message: ChatCompletionMessageParam, de
 
     Args:
         model (str): The name of the model to use for encoding.
-        message (Mapping): The message to encode, in a dictionary-like object.
+        message (dict): The message to encode, in a dictionary-like object.
         default_to_cl100k (bool): Whether to default to the CL100k encoding if the model is not found.
     Returns:
         int: The total number of tokens required to encode the message.
@@ -116,8 +116,14 @@ def count_tokens_for_message(model: str, message: ChatCompletionMessageParam, de
                     num_tokens += len(encoding.encode(item["text"]))
                 elif item["type"] == "image_url":
                     num_tokens += count_tokens_for_image(item["image_url"]["url"], item["image_url"]["detail"], model)
+                elif item["type"] == "function":
+                    num_tokens += 1     #   A guess, to be revised. What is the impact of a tool/function call on tokens?
         elif isinstance(value, str):
             num_tokens += len(encoding.encode(value))
+        elif (key in ["content", "refusal", "function_call"] and value is None 
+            and message.get("role")=="assistant" 
+            and message.get("tool_calls") is not None):     # If the model calls a tool/function then content can be None
+            num_tokens += 0     #   a guess at this stage, to be revised
         else:
             raise ValueError(f"Could not encode unsupported message value type: {type(value)}")
         if key == "name":