# How do I trace a LangGraph agent?

LangGraph traces through LangSmith, not through a built-in OpenTelemetry exporter, so reaching your own backend means turning on LangSmith's OTLP export rather than pointing a generic OTel SDK at the graph. Set `LANGSMITH_TRACING=true` and `LANGSMITH_OTEL_ENABLED=true`, then point `OTEL_EXPORTER_OTLP_ENDPOINT` at your collector: LangSmith exports the same spans it always recorded, over the standard protocol, instead of keeping them in its own UI only.

Because LangGraph saves state after every step, keyed by a thread id, each node's span identifies exactly where in the graph a run was when it produced a given output, not just that the agent as a whole did something. That's also what real replay depends on: rewinding to a saved checkpoint and running forward again with the exact state the graph had at the time, rather than a reconstruction from a paraphrased retry. It's the same [instrumentation](/answers/instrumentation/what-is-agent-instrumentation) job any agent needs, just scoped to one node instead of one whole turn, which is what makes "the router picked the wrong branch" a separate, gradeable finding from "the final answer was wrong."

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Sources:
- LangChain docs: Trace with OpenTelemetry: https://docs.langchain.com/langsmith/trace-with-opentelemetry (fetched 2026-09-11)

Source: https://tessary.ai/answers/langgraph-evals/how-do-i-trace-a-langgraph-agent
More on Langgraph evals: https://tessary.ai/answers/langgraph-evals
From Tessary, agent reliability for AI agents in production: https://tessary.ai