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Install the packages:
Create a filesystem-backed trace store:

Attach the Tracer

Pass the tracer through LangGraph or LangChain callback options:
flush() waits for in-flight callback writes, batches pending runs, and writes the final trace snapshots. Call it before your script exits or before you expect the trace viewer to show the latest run.

Run the Viewer

Start the local viewer against the same trace root:
Open http://127.0.0.1:4319. The viewer lists traces, shows the run tree, and lazy-loads input/output payloads when you select a run.

Try the Repository Example

From the repository root:
The example builds a mock LangGraph workflow with planner, researcher, lookup, summarizer, and reviewer nodes so the viewer has a nested trace tree to inspect.