Langchain is a framework for building AI Agents by combining LLMs and tool calling. Since it is compatible with OpenAI API it is able to communicate with most LLMs
Structured Output
Langchain provides integration with pydantic which uses function calling under the covers to force models to respond in a structured format.
Tool Calling and Artifacts
Lankchain allows you to cull tools and to preserve part of the output as local state which does not get fed to the LLM as part of the context. These outfits are called artifacts.