The strongest open-source alternatives to LangSmith for building AI agents — observability & evals (managed) ranked by GitHub traction, each with a head-to-head.
Short answer: the closest alternative to LangSmith is Arize Phoenix / AX (★ 0), the most-starred observability & evals (managed); Braintrust and Comet Opik are also strong.
LangSmith (★ 0) is LangChain's managed tracing, evaluation and prompt-engineering platform for LLM and agent apps. If it is not the right fit, these 15 observability & evals (managed) cover the same ground — Arize Phoenix / AX is the most-starred option below. Or browse the best observability & evals (managed) and LangSmith's own page.
Open-source LLM/agent observability (Phoenix) plus Arize AX, the commercial platform for production monitoring and online evals. Best for agent builders.
Eval-first AI platform unifying evaluations, tracing/logging and prompt playground for shipping quality AI products. Best for agent builders.
Open-source LLM tracing, LLM-as-a-judge evals and experiment management from Comet, with a managed cloud. Best for agent builders.
Cloud AI-quality platform on top of the open-source DeepEval framework: test management, tracing and analytics. Best for agent builders.
LLM/agent observability inside Datadog's APM suite, billing only on LLM spans with built-in online/offline evals. Best for agent builders.
All-in-one evaluate/observe/improve platform for LLM and agent apps: tracing, evals, simulations, gateway and guardrails. Best for agent builders.
Enterprise AI evaluation + observability platform where offline evals become production guardrails (now part of Cisco). Best for agent builders.
OpenTelemetry-based observability and evaluation platform purpose-built for production AI agents. Best for agent builders.
Open-source-core LLM observability with tracing, evals, prompt management and playground, offered as a managed cloud. Best for agent builders.
OpenTelemetry-native, open-source tracing and metrics for LLM, vector-DB and framework calls, with a hosted cloud. Best for agent builders.
Lightweight open-source LLM observability, prompt management and analytics, tuned for chatbots and RAG. Best for agent builders.
End-to-end GenAI platform to simulate, evaluate and observe agents, with prompt versioning and online evals. Best for agent builders.
Prompt management + LLM observability platform for versioning prompts, running evals and tracing agents in production. Best for agent builders.
LLM reliability platform built on OpenLLMetry, an OpenTelemetry-native tracing layer for LLM apps. Best for agent builders.
Weights & Biases' LLM observability and evaluation toolkit that auto-traces calls and runs LLM-judge scorers. Best for agent builders.
Arize Phoenix / AX (★ 0) is the most-starred observability & evals (managed) alternative to LangSmith. Open-source LLM/agent observability (Phoenix) plus Arize AX, the commercial platform for production monitoring and online evals.
The strongest observability & evals (managed) alternatives to LangSmith are Arize Phoenix / AX, Braintrust, Comet Opik, Confident AI (DeepEval) and more — each with a head-to-head comparison.
Yes — the alternatives listed are open source and free to self-host; you bring your own model keys.
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