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Term of the Day · May 31, 2026

LangSmith

LangSmith is LangChain's commercial LLM observability and evaluation platform. It captures traces (LangChain-native and OTel), runs evaluations, manages prompt versions, and supports dataset curation.

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Related concepts

LLM ObservabilityInfrastructure

LLM observability is the practice of capturing, analyzing, and acting on every LLM call in a production system — inputs, outputs, latencies, costs, errors, and quality scores — so you can debug regressions and improve quality over time.

TracingInfrastructure

Tracing captures the full causal tree of an LLM request — the user input, retrieval calls, tool calls, intermediate prompts, and the final response — as a hierarchy of timed spans you can replay and inspect.

Arize PhoenixInfrastructure

Arize Phoenix is an open-source LLM observability and evaluation tool. It ingests OpenTelemetry traces, renders them in a debug UI, and provides built-in LLM-as-judge evaluators for hallucination, relevance, and toxicity.

LangfuseInfrastructure

Langfuse is an open-source LLM observability platform with tracing, prompt management, evaluation, and a self-host option. Popular default for teams who want LangSmith-equivalent tooling without the SaaS lock-in.

Online EvaluationEvaluation

Online evaluation runs scoring functions over live production traffic — usually a sample of recent traces — to monitor quality continuously instead of relying solely on a fixed offline dataset.

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