LangChain fundamentals part 2: structured outputs and tool calling

This is where LangChain stops being a convenience layer and starts becoming genuinely powerful. If you missed part 1, start there — it covers the Runnable protocol and LCEL, the mental model everything else builds on. Concept 4 — structured outputs Raw LLM responses are strings. Real applications need JSON — predictable, parseable, typed data your code can actually work with. LangChain gives you two approaches. The more reliable one is .with_structured_output() , which uses your Pydantic model t