Structured output

Supported models and endpoint

Use POST /v1/messages with output_config.format and one of these models:

• openai/gpt-4.1-mini
• anthropic/claude-opus-5

Schema output supports JSON responses and streaming on these models. Your key must allow the model and an available provider that supports schema output. No routing override or structured-output beta header is needed.

Chat Completions response_format and Responses text.format are not currently supported for schema-constrained output. A model's ability to write JSON in ordinary chat does not enforce a schema.

Set your key

Create an API key, save its recovery link, and add credits. Replace the placeholder below and run it in your terminal before running the examples on this page.

export MINIROUTER_KEY='paste-your-api-key-here'

Examples use paid models. For free requests, follow the Auto Free guide.

Send a schema request

Run this in the same terminal. The schema requires both fields and rejects extra properties.

curl https://api.minirouter.sh/v1/messages \
  -H "Authorization: Bearer $MINIROUTER_KEY" \
  -H "Content-Type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
  "model": "openai/gpt-4.1-mini",
  "max_tokens": 256,
  "messages": [
    {
      "role": "user",
      "content": "Extract the city and country: I live in Paris, France."
    }
  ],
  "output_config": {
    "format": {
      "type": "json_schema",
      "schema": {
        "type": "object",
        "properties": {
          "city": {
            "type": "string"
          },
          "country": {
            "type": "string"
          }
        },
        "required": [
          "city",
          "country"
        ],
        "additionalProperties": false
      }
    }
  }
}'

To extract different data, change the prompt and the properties and required entries in the schema. Keep additionalProperties: false for an object with only the named fields.

Read and validate the result

A successful Messages response contains text blocks in its content array. Join the text values from blocks whose type is text, then parse that string as JSON. The text for this example should have this shape:

{"city":"Paris","country":"France"}

Check the response status and stop_reason before using the object. A refusal, error or max_tokens stop is not a completed schema result. Validate the parsed object against your schema in your application.

Stream structured output

Add "stream": true to the same request and use curl -N. Collect text from content_block_delta events with delta.type: "text_delta". Wait for message_stop, check the final stop reason, and then parse the complete text. Individual chunks may contain only part of a JSON token.

Troubleshooting

• 400 invalid_request_error: check the model, endpoint and output_config.format shape. Simplify a schema that exceeds request limits.
• A truncated response: increase max_tokens or ask for a smaller object.
• A refusal: handle it separately from schema output; do not parse it as your data object.
• No eligible provider: check your key's model and provider restrictions, or try again later.

Thinking and tool controls have separate model requirements. Start with the schema-only request above, then add supported controls one at a time.