Easy to do and not a bad idea. You don't need to pass structured output and accept structured input: in the end, an LLM uses any readable text. A tool is just a way for an LLM to ask questions of a certain type and wait for the answer. For example, I'm wondering if certain flows could be improved by a "ask_clarification_question" tool that simply displays the question in the chat and returns the answer.
I understand that this is not exactly in the spirit of your question but, well, a tool is just this.