Awesome job with the simplicity, gonna play with it. Have you tried using yaml as the format with the models instead of JSOn? Feel like you'll use far fewer tokens to describe the same thing. Perhaps it's a bit more forgiving as well.

EDIT: Just tried using the decorator to output a fairly complex pydantic model and it failed with "magentic.chat_model.openai_chat_model.StructuredOutputError: Failed to parse model output. You may need to update your prompt to encourage the model to return a specific type."

I typically try to give examples in the pydantic Config class, perhaps those could be piped in for some few-shot methods, and also have some iteration if the model output is not perfectly parseable to correct the output syntax..