# Redact PII with LangChain

> Wrap a LangChain prompt so personal data is removed before the request reaches the model provider.

Canonical: https://bitbanger.in/integrations/langchain
Last updated: 2026-10-27

LangChain makes it easy to send arbitrary text to a provider, which also makes it easy to send personal data. A small transform between the prompt and the model fixes that without changing the rest of the chain.

## Code

```
import requests
from langchain_core.prompts import ChatPromptTemplate

def redact(text: str) -> str:
    r = requests.post(
        "https://api.bitbanger.in/v1/redact",
        headers={"X-API-Key": "rdct_your_key_here"},
        json={"text": text},
        timeout=30,
    )
    r.raise_for_status()
    return r.json()["redacted"]

prompt = ChatPromptTemplate.from_template(
    "Summarise this support message: {message}"
)
safe_prompt = prompt | (lambda values: {**values, "message": redact(values["message"])})
chain = safe_prompt | model
```

## Notes

- Redact before the prompt is formatted, not after, so the original never enters the chain's traces.
- LangSmith and other tracers record inputs by default; redacting first keeps those traces clean too.
- The same wrapper works with any provider, because it operates on the string rather than the client.

## Related

- [API reference](https://bitbanger.in/docs)
- [Playground](https://bitbanger.in/redact)
- [All 40 entity types](https://bitbanger.in/entities/)