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​
Minimal request

{
  "model": "gemini-2.5-flash",
  "contents": [
    {
      "role": "user",
      "parts": [{ "text": "Get today's Shanghai weather." }]
    }
  ],
  "tools": [
    {
      "functionDeclarations": [
        {
          "name": "get_weather",
          "description": "Fetch weather",
          "parameters": {
            "type": "object",
            "properties": {
              "city": { "type": "string" }
            },
            "required": ["city"]
          }
        }
      ]
    }
  ]
}

​
cURL example

curl "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent" \
  -H "x-goog-api-key: $GEMINI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "contents": [
      {
        "role": "user",
        "parts": [{ "text": "Get today'\''s Shanghai weather." }]
      }
    ],
    "tools": [
      {
        "functionDeclarations": [
          {
            "name": "get_weather",
            "description": "Fetch weather",
            "parameters": {
              "type": "object",
              "properties": {
                "city": { "type": "string" }
              },
              "required": ["city"]
            }
          }
        ]
      }
    ]
  }'

​
Python example

import requests

response = requests.post(
    "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent",
    headers={
        "x-goog-api-key": "<GEMINI_API_KEY>",
        "Content-Type": "application/json",
    },
    json={
        "contents": [
            {
                "role": "user",
                "parts": [{"text": "Get today's Shanghai weather."}],
            }
        ],
        "tools": [
            {
                "functionDeclarations": [
                    {
                        "name": "get_weather",
                        "description": "Fetch weather",
                        "parameters": {
                            "type": "object",
                            "properties": {
                                "city": {"type": "string"},
                            },
                            "required": ["city"],
                        },
                    }
                ]
            }
        ],
    },
)

print(response.json())

​
Node.js example

const response = await fetch(
  "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent",
  {
    method: "POST",
    headers: {
      "x-goog-api-key": process.env.GEMINI_API_KEY,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      contents: [
        {
          role: "user",
          parts: [{ text: "Get today's Shanghai weather." }]
        }
      ],
      tools: [
        {
          functionDeclarations: [
            {
              name: "get_weather",
              description: "Fetch weather",
              parameters: {
                type: "object",
                properties: {
                  city: { type: "string" }
                },
                required: ["city"]
              }
            }
          ]
        }
      ]
    }),
  }
);

console.log(await response.json());

​
Best practices

  • Gemini function declarations need their own mapping layer
  • If you enable multiple tool calls, the executor should support batch or chained execution
  • Detailed descriptions matter more than short function names