Get schema-conforming JSON from Ollama with structured outputs (format = JSON schema) on /api/generate or /api/chat
domain: ollama.com · 5 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Set the format parameter to a JSON schema object, e.g. format: {"type": "object", "properties": {"age": {"type": "integer"}, "available": {"type": "boolean"}}, "required": ["age", "available"]}.
Works on both POST /api/generate (schema constrains response) and POST /api/chat (constrains message.content).
The constrained output arrives as a JSON-encoded string in response (generate) or message.content (chat) — json.loads it to get the object.
Set options: {"temperature": 0} for more deterministic extraction, and stream: false so you can parse the whole payload at once.
Still tell the model in the prompt to respond as JSON matching what you want — the schema constrains decoding, the prompt guides content.
Known gotchas
The result is a string field containing JSON, not a nested object — you must parse it.
format accepts either the literal string "json" (free-form JSON mode) or a schema object; these are different behaviors.
Very restrictive schemas plus an off-topic prompt can yield empty/degenerate values — the schema forces shape, not truthfulness.
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