You should also be ready to handle and return parallel tool calls.
In another post, I wrote a demonstration of the messages used for each role. It has a tool specification, and also what the second call back to an AI needs to receive in addition. You can run that script to get the AI calling tools, to work with the object methods of python, or just see the json.
Your code for handling - constructing the message contents instead of showing - will be more impenetrable…