LangChain

LangChain is a free, open-source developer framework for building AI agents and applications. It uses a pattern called ReAct, where the model reasons about a task and takes actions in a loop, and developers can add middleware such as requiring human approval before an action or removing sensitive data from a request. It standardizes how agents call models, tools, and databases, so teams can switch between providers like OpenAI, Anthropic, Google, or AWS Bedrock without rewriting the whole application. It is licensed under MIT. The company also sells LangSmith, a separate paid platform for monitoring, testing, and deploying agents built with LangChain or LangGraph.

This fits an engineering team that wants a common set of building blocks for agents rather than writing every integration by hand, especially one that expects to try more than one model provider over time. A typical starting point is rebuilding one existing manual process as a small agent, such as document summarization or ticket routing, scaling up only after that works. The framework itself is free; the real cost is developer time plus the API usage of whatever model it connects to, and a separate LangSmith subscription if you add monitoring, priced by the vendor rather than published. The main risk with any fast-moving open-source framework is breaking changes between versions, so plan maintenance time and pin dependency versions in production.