LangSmith

LangSmith is the agent engineering platform from LangChain, the company behind the LangChain and LangGraph frameworks. It started as a tracing and debugging tool for LangChain apps and has grown into a hosted stack for observing, evaluating, and running agents in production. It is framework-agnostic: SDKs for Python and TypeScript, a traceable decorator for plain code, and end-to-end OpenTelemetry support let any application send traces, though the deepest views are built around LangGraph.

Its core is tracing: every request becomes a trace of nested runs covering model calls, tool calls, retrieval, and agent steps, with token, cost, and latency data attached. Monitoring dashboards and alerts sit on top, and the Insights Agent clusters production traces to surface common usage patterns and failure modes. Evaluations cover offline test datasets, online scoring of live traffic, LLM-as-judge and heuristic evaluators, pairwise comparisons, multi-turn conversation evals, and human annotation queues. A prompt hub and playground handle prompt versioning and testing.

Beyond observability, LangSmith now covers agent deployment. LangSmith Deployment (formerly LangGraph Platform) hosts agents as scalable APIs with persistence and background runs, Studio provides a visual debugger for stepping through graphs, and Fleet (formerly Agent Builder) lets non-technical staff describe agents in natural language under admin-controlled permissions.

LangSmith is a proprietary, cloud-first service with a free Developer plan, a per-seat Plus plan billed with trace overages, and an Enterprise plan that adds self-hosting in the customer's own cloud, SSO, and compliance features. Teams that want an open-source, freely self-hostable equivalent usually choose Langfuse instead.