LangChain
Open SourceFrameworks & SDKs
The de facto framework for building LLM applications.
What it’s for
LangChain gives you composable primitives — prompt templates, chains, agents, retrievers and hundreds of integrations — to build anything from a chatbot to a multi-step agent pipeline, in Python or JavaScript. It shines when many components need to talk to each other.
How to use it
Install with pip or npm, compose a chain (prompt template → model → output parser), then layer on agents, tools and memory as your app grows. Pair it with LangSmith when you need tracing and evals in production.
Pricing
The framework is MIT licensed and free. LangSmith, its companion platform for tracing and evaluation, is a separate paid product with a free tier.