Anthropic Knowledge Hub

SOP: Enforce Structured Outputs ​

Updated: 2026-05-26

Force Claude to return valid JSON matching a specific schema, with no extra text.

Prerequisites ​

  • Messages API integration working
  • JSON Schema for your desired output format

Steps ​

Step 1: Define Your Output Schema ​

python
response_format = {
    "type": "json_schema",
    "name": "sentiment_analysis",
    "schema": {
        "type": "object",
        "properties": {
            "sentiment": {"type": "string", "enum": ["positive", "negative", "neutral"]},
            "confidence": {"type": "number", "minimum": 0, "maximum": 1},
            "key_phrases": {"type": "array", "items": {"type": "string"}}
        },
        "required": ["sentiment", "confidence", "key_phrases"]
    }
}

Step 2: Send Request with Response Format ​

bash
curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Analyze: The product exceeded our expectations"}
    ],
    "response_format": {
      "type": "json_schema",
      "name": "sentiment_analysis",
      "schema": {
        "type": "object",
        "properties": {
          "sentiment": {"type": "string", "enum": ["positive", "negative", "neutral"]},
          "confidence": {"type": "number"},
          "key_phrases": {"type": "array", "items": {"type": "string"}}
        },
        "required": ["sentiment", "confidence", "key_phrases"]
      }
    }
  }'

Step 3: Parse and Validate ​

The response will contain only JSON text. Parse and validate against your schema:

python
import json
response_text = response.content[0].text
parsed = json.loads(response_text)
assert "sentiment" in parsed
assert parsed["sentiment"] in ["positive", "negative", "neutral"]

Verification Checklist ​

  • [ ] Response is parseable JSON (no markdown wrapper, no preamble)
  • [ ] All required fields present
  • [ ] Enum values match allowed options
  • [ ] No extra text outside the JSON object

See Also ​