LLM APIs, All in One Go — Prompts, Structured Outputs, and Tool Calling

I sent the same request twice and got different answers. Which one can I use in my program? We’ll walk through actual API call logs on screen, step by step, examining the structure of requests and responses, structured outputs, streaming, tool calls, errors and retries, and costs. Instead of treating the mere arrival of text as success, we’ll establish criteria for accepting or holding a response based on its status, format, evidence, and cost.