LangSmith / LangChain API
LangSmith / LangChain API
LangSmith API is LangChain's LLM application observability platform — trace LLM calls, debug prompts, eval output quality, monitor production LLM apps.
Native LangChain ecosystem (LangChain code auto-traces)
Usable without LangChain but ecosystem advantage smaller
Create API key at smith.langchain.com. Python: import langsmith; auto-trace (LANGCHAIN_TRACING_V2=true env var).
Uptime · 30-day window
About this API
LangSmith is LangChain Inc.'s commercial product launched 2023. Background: LangChain is the most popular LLM app framework (Python + TypeScript, 90k+ GitHub stars), letting developers build chains, agents, RAGs in a few lines. But production LLM agents involve dozens of LLM calls, tool calls, retrievals — debugging and monitoring is hard. LangSmith solves this: report all LangChain (or pure OpenAI SDK) execution traces to cloud; UI shows complete call tree (which LLM call, prompt, output, latency, cost). Also provides eval framework — human eval / LLM-as-judge / heuristic for scoring LLM outputs, A/B testing prompt versions. One of de-facto observability standards for production LLM apps (other options: Helicone, Langfuse).
What you can build
- 1End-to-end tracing for production LLM apps
- 2Prompt debugging and iteration (A/B test prompt versions)
- 3Automatic eval of LLM output quality
- 4Multi-step AI agent call visualization debugging
Strengths & limitations
Strengths
- Native LangChain ecosystem (LangChain code auto-traces)
- Eval framework supports human + LLM-as-judge + heuristic
- Prompt playground / version management
Limitations
- Usable without LangChain but ecosystem advantage smaller
- 5000 traces free tier insufficient for production
Example request
curl https://www.langchain.com/<endpoint> \
-H "Authorization: Bearer $API_KEY"
# Some providers use X-Api-Key instead — verify in the docs.Getting started
Create API key at smith.langchain.com. Python: import langsmith; auto-trace (LANGCHAIN_TRACING_V2=true env var).
FAQ
Can I use LangSmith without LangChain?+
Yes. Use langsmith SDK to directly trace any LLM call (OpenAI / Anthropic direct). But LangChain integration is much deeper.
LangSmith vs. Helicone?+
LangSmith: ecosystem advantage (large LangChain user base). Helicone: one-line code (proxy mode) + cheaper.
Technical details
- Auth type
- api_key
- Pricing
- freemium
- Rate limit
- 免费 5000 traces/月；Plus $39/月
- Protocols
- REST
- SDKs
- python, typescript, javascript