LangChain
Popular open-source framework for composing LLM-powered applications and agents with a unified interface across model providers.
About
LangChain is a developer framework that simplifies building applications around large language models. It provides a standard interface for working with chat models and embeddings from dozens of providers, and lets you wire together tools, prompts, and middleware into configurable agent harnesses. Complex workflows that mix deterministic logic with agentic behavior are handled through its companion library LangGraph, which adds durable execution and human-in-the-loop capabilities. LangSmith integrates for tracing, debugging, and evaluating agents in production. The core framework is open source and free; LangSmith and cloud services have paid plans.