Guides
JSON mode

JSON mode

Force the model to return strict JSON.

Usage

resp = client.chat.completions.create(
    model="deepseek-v3.2",
    messages=[
        {"role": "system", "content": "Respond only with JSON."},
        {"role": "user", "content": "Three colors as RGB"}
    ],
    response_format={"type": "json_object"},
)
 
import json
data = json.loads(resp.choices[0].message.content)

Required for JSON mode

  • The system prompt must mention "JSON" — most models enforce this
  • Include schema constraints in the prompt for best results

Schema-constrained mode

Pass a JSON schema for stricter validation:

response_format={
    "type": "json_schema",
    "json_schema": {
        "name": "color_palette",
        "schema": {
            "type": "object",
            "properties": {
                "colors": {
                    "type": "array",
                    "items": {"type": "string", "pattern": "^#[0-9A-Fa-f]{6}$"}
                }
            }
        }
    }
}

Supported by:

  • gpt-4o, o1
  • claude-sonnet-4-6, claude-opus-4-7
  • kimi-k2.5, glm-4.6 (best-effort)
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