03·Tool/function calling schemas

Introduction

Tool calling is an API contract between the model and the app. In this lesson: how the definition shape differs across OpenAI, Anthropic, Gemini; the role of description as prompt; tool_choice and parallel_tool_calls; multi-turn tool_result handling; type coercion pitfalls, hallucinated names and arguments; namespacing for large toolsets; MCP as one standard; SDK abstractions; security and cost; why the god-tool is an anti-pattern.