# tinker_cookbook.exceptions.DataFormatError

## *class* [**tinker_cookbook.exceptions.DataFormatError**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/exceptions.py#L97)(*[DataError](https://tinker-docs.thinkingmachines.ai/cookbook/api-reference/exceptions/dataerror/index.md)*)

Data is not in the expected format.

Raised when input data (JSONL files, HuggingFace datasets, conversation dicts, etc.) is structurally malformed — e.g. a missing `messages` field in a JSONL line, or a conversation with too few tokens.