LangSmith is LangChain's production monitoring, testing, and debugging platform for LLM applications, providing the observability layer that AI teams need to build reliable AI products. It captures every LLM call, agent action, and chain execution with full context, enabling developers to trace failures, compare model outputs, run regression tests, and monitor production performance in real-time. LangSmith integrates seamlessly with LangChain and LangGraph but also works with any LLM framework, making it the standard choice for teams that need confidence in their AI application quality.