LangSmith, from the LangChain team, is a platform for debugging, testing, evaluating, and monitoring LLM applications. You instrument your app, and LangSmith captures every trace — prompts, tool calls, token usage, latency — so you can inspect runs, build evaluation datasets, and track quality over time. It is framework-agnostic and not limited to coding agents; teams use it for chatbots, RAG pipelines, and any LLM workload.
Fleet is not an observability platform. It is the governed workflow layer that runs Claude Code agents against your repositories. You save a typed workflow graph, start a run manually, on a schedule, or from a GitHub label, and route code, review, approval, publish, and merge steps through explicit bounded edges. Where LangSmith answers 'what did my LLM calls do and how good were they?', Fleet answers 'who does what, in what order, and with what guardrails?'.