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Tool Calling

The OpenResponses API supports tool calling to give models access to external functions. Define tools in your request with a name, description, and JSON schema for parameters. When the model determines it needs a tool to answer the user's question, it returns a function_call output with the tool name and arguments for you to execute.

import requests
import json

url = "https://llm.siraya.ai/v1/responses"

headers = {
    "Content-Type": "application/json",
    "Authorization": "Bearer <API_KEY>",
}

data = {
    "model": "gemini-2.5-pro",
    "input": [
        {
            "type": "message",
            "role": "user",
            "content": "What is the weather like in New York?",
        }
    ],
    "tools": [
        {
            "type": "function",
            "function": {
                "name": "get_weather",
                "description": "Get the current weather in a location",
                "parameters": {
                    "type": "object",
                    "properties": {
                        "location": {
                            "type": "string",
                            "description": "The city and state, e.g. San Francisco, CA",
                        },
                    },
                    "required": ["location"],
                },
            },
        }
    ],
    "tool_choice": "auto",
}

response = requests.post(url, headers=headers, json=data)
response.raise_for_status()
result = response.json()

print(json.dumps(result, indent=2))

const response = await fetch('https://llm.siraya.ai/v1/responses', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    Authorization: `Bearer <API_KEY>`,
  },
  body: JSON.stringify({
    model: 'gemini-2.5-pro',
    input: [
      {
        type: 'message',
        role: 'user',
        content: 'What is the weather like in New York?',
      },
    ],
    tools: [
      {
        type: 'function',
        function: {
          name: 'get_weather',
          description: 'Get the current weather in a location',
          parameters: {
            type: 'object',
            properties: {
              location: {
                type: 'string',
                description: 'The city and state, e.g. San Francisco, CA',
              },
            },
            required: ['location'],
          },
        },
      },
    ],
    tool_choice: 'auto',
  }),
});

Tool call response

When the model decides to call a tool, the response includes a function_call output:

{
  "id": "resp_chatcmpl-vertexai-abcdefghijklmnopqrstuvwx",
  "object": "response",
  "created_at": 1774723206,
  "status": "completed",
  "model": "gemini-2.5-pro",
  "output": [
    {
      "type": "function_call",
      "id": "call_abcdefghijklmnopqrstuvwx",
      "status": "completed",
      "call_id": "call_abcdefghijklmnopqrstuvwx",
      "name": "get_weather",
      "arguments": "{\"location\":\"New York\"}"
    }
  ],
  "usage": {
    "input_tokens": 23,
    "output_tokens": 61,
    "total_tokens": 84,
    "output_tokens_details": {
      "reasoning_tokens": 55
    }
  }
}

Tool choice options

  • auto - The model decides whether to call a tool
  • required - The model must call at least one tool
  • none - The model cannot call any tools