Thank you for reaching out to us on the Microsoft Q&A forum.
Based on your description we understand that you’re going through Azure OpenAI.
Azure OpenAI supports all the data formats what you mentioned above is correct.
In Azure, JSON is commonly used for configuration, data interchange, and messaging due to its lightweight and human readable. While other formats like .txt .md...etc are suitable for specific types of data (such as text documents, presentations, or structured documents), JSON is well supported by Azure tools and services, simplifying integration and development processes.
For additional reference on the JSON format and Data formats and file types kindly follow the links given below:
The JSON format: https://learn.microsoft.com/en-us/azure/data-explorer/ingest-json-formats?tabs=kusto-query-language#the-json-format
Data formats and file types: https://learn.microsoft.com/en-us/azure/ai-services/openai/concepts/use-your-data?tabs=ai-search#data-formats-and-file-types
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