LangChain

LangChain is an open-source framework, in Python and JavaScript, for building applications and agents on top of large language models. The README describes it as a framework for building agents and LLM-powered applications, with interoperable components and third-party integrations for chat and embedding models, tools, vector stores and retrievers. The framework is MIT-licensed and free to self-host. The company was incorporated in April 2023 (founded by Harrison Chase) and is headquartered in San Francisco.

The Python package installs with uv add langchain, and a JS and TypeScript equivalent, LangChain.js, is available. For more advanced customization the README points to LangGraph, its framework for controllable agent workflows, and to Deep Agents, a higher-level package for agents that plan, use subagents and work with file systems. Because models are swappable behind a common interface, a team can compare providers without rewriting application code.

The company separately sells LangSmith, a hosted platform for agent evaluation, observability, debugging and deployment, with a free-to-start plus usage-based plan. The Developer plan is $0 per seat per month for one seat, the Plus plan is $39 per seat per month, and the Enterprise plan adds self-hosted and hybrid deployment options. LangChain says deployments can run as SaaS, bring-your-own-cloud or self-hosted.

Typical uses are retrieval-augmented applications, tool-calling agents and long-running, stateful agent workflows. LangChain also publishes LangChain Academy, a set of free courses on its libraries and products.