# Instrument LangChain

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Canonical sample: [`samples/integrations/langchain_instrumented.py`](https://github.com/layerlens/stratix-python/blob/main/samples/integrations/langchain_instrumented.py) — auto-capture LangChain LCEL chain execution with `LangChainCallbackHandler`. Drop-in: no manual trace upload needed.

## Quick wire-up

```bash
pip install 'layerlens[providers-openai]' # plus your LangChain extras
```

```python
from layerlens import Stratix
from layerlens.instrument.adapters.frameworks.langchain import LangChainCallbackHandler

client = Stratix()
handler = LangChainCallbackHandler(client)
chain.invoke(input, config={"callbacks": [handler]})
```

The handler emits `model.invoke`, `cost.record`, and `tool.call` events to the configured HTTP sink.

## See also

* [SDK sample: `langchain_instrumented.py`](https://github.com/layerlens/stratix-python/blob/main/samples/integrations/langchain_instrumented.py)
* [SDK adapter doc: LangChain](https://github.com/layerlens/stratix-python/blob/main/docs/adapters/frameworks-langchain.md)
* [Integrations](/6.-build-wire-your-code/migration.md)


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