# merge_headers

> **Function** in `langsmith`

📖 [View in docs](https://reference.langchain.com/python/langsmith/sandbox/_helpers/merge_headers)

Merge request headers, giving precedence to overrides.

Names are normalized to lowercase so an override replaces a base header that
differs only in casing. HTTP header names are case-insensitive, so keeping
both would be ambiguous — a server reading the first value would see the
base header instead of the override.

## Signature

```python
merge_headers(
    base_headers: Optional[Mapping[str, str]] = None,
    override_headers: Optional[Mapping[str, str]] = None,
) -> dict[str, str]
```

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[View source on GitHub](https://github.com/langchain-ai/langsmith-sdk/blob/52e79add98f6559235d1eb00f5f533b9be6d4cf6/python/langsmith/sandbox/_helpers.py#L33)