VercelVercel
Menu

Tool Calling

Last updated January 15, 2026

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 decides a tool would help answer the user's question, it returns a function_call output with the tool name and arguments for you to execute.

tool-calls.ts
const apiKey = process.env.AI_GATEWAY_API_KEY;
 
const response = await fetch('https://ai-gateway.vercel.sh/v1/responses', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    Authorization: `Bearer ${apiKey}`,
  },
  body: JSON.stringify({
    model: 'deepseek/deepseek-v3.2-thinking',
    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:

{
  "output": [
    {
      "type": "function_call",
      "name": "get_weather",
      "arguments": "{\"location\": \"New York, NY\"}",
      "call_id": "call_abc123"
    }
  ]
}

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

Was this helpful?

supported.