LangGraphLangGraph 1.2 · Python 3.10+
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38 small wins to finish your path

LangSmith: see what a run did

LangSmith records every run so you can read it back step by step. You set two environment variables before running, and tracing turns on with no code change.

Last updated: 27 Sep, 2026 · LangSmith

When an answer is wrong, logs rarely show why. A trace shows each node, each model call, and what it sent and got back, so you can find the step that failed.

The tracing environment variables

python
export LANGSMITH_TRACING=true
export LANGSMITH_API_KEY=your_key
export LANGSMITH_PROJECT=support-agent   # optional

What tracing records

  • With those variables set, LangChain and LangGraph detect them and trace every run automatically, no code change needed.
  • Each run appears in LangSmith as a tree of steps you can open and read.
  • The older LANGCHAIN_TRACING_V2 and LANGCHAIN_API_KEY names still work; the LANGSMITH_ names are current.

When to turn on tracing

  • Finding the step where a run went wrong or got expensive.
  • Watching what a live agent sends to the model.
Watch out. Tracing records runs only after it is switched on. Set the variables before you run, or the run you wanted to inspect is not captured. Turn it on before you need it.
Try it yourself
  • Set the variables, run any earlier lesson's graph, and open the trace.
  • Name the project and confirm the run lands under it.
PreviousDeploy: langgraph dev and langgraph.json

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