XML Envelopes, JSON Payloads: The Gold Standard for Production LLM Output

This article exposes a critical misconception about LLM output formatting: developers typically view JSON and XML as competing choices, when in fact they serve different purposes. The real solution combines XML tags as delimiters (allowing the model to include conversational context) with JSON as the data format (maintaining strict schema). This hybrid approach is essential as production systems encounter increasingly unpredictable model behavior across languages and contexts.