OpenRouter explains three ways to get reliable structured output from any LLM
AIOpenRouter says LLM structured output can be obtained with a strict JSON Schema, a forced tool call, or a decision model, depending on the model's support. In a test of 24 messy support messages on nine structured-output models plus GLM 5.3 FlashX, 209 of 216 replies matched a strict schema, while prompt-only JSON requests failed 18 times because of code fences.
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OpenRouter Blog · openrouter.aiPublished · added here
Original title: How to Get Structured Output from Any LLM: JSON Schema, Tool Calls, or a Decision Model