Been working with OpenAI's API for a few months now and I'm curious about other devs' experiences with structured outputs vs function calling.
I've been using function calling for most of my workflow automation stuff - like when I need the model to decide between sending an email, creating a calendar event, or updating a database record. Works great for that.
But lately I've been experimenting with structured outputs (the JSON schema approach) for data extraction tasks. Just migrated a customer feedback parser from function calling to structured outputs and honestly... it feels cleaner? Instead of defining a function with parameters, I just specify the JSON schema I want:
{
"type": "object",
"properties": {
"sentiment": {"type": "string", "enum": ["positive", "negative", "neutral"]},
"key_issues": {"type": "array", "items": {"type": "string"}}
}
}
Response consistency seems better too - went from ~85% properly formatted responses to basically 100% with structured outputs.
My current thinking: function calling when I need the model to actually DO something, structured outputs when I just want data in a specific format. But I'm probably missing nuances here.
Anyone have experience with both? What's your decision framework for choosing between them?
I've been A/B testing both approaches in my e-commerce chatbot. Function calling gives me ~89% accuracy for intent classification (buy/browse/support) but structured outputs hit 94% for product recommendations with complex filtering. The latency difference is minimal - about 20ms slower for structured outputs but totally worth it when I need guaranteed JSON schema compliance. My parsing errors dropped from 12% to basically zero after switching product queries to structured outputs.
YES! This is exactly what I've been telling my team! Function calling is perfect for those action-based workflows you mentioned. But here's the game changer - try structured outputs for any data extraction tasks. Pro tip: use Pydantic models to define your schemas beforehand, makes debugging so much easier. Also found that combining both works amazingly well - use function calling to determine the action, then structured outputs for the data formatting. Best of both worlds!