Function calling and Gemini tools

const model = "gemini-3.8-flash"; // Or any listed Seed, DeepSeek, or GLM LLM.
const tools = [{
  type: "function",
  function: {
    name: "get_weather",
    description: "Get the current weather in a city",
    parameters: {
      type: "object",
      properties: { city: { type: "string" } },
      required: ["city"],
    },
  },
}];
const messages = [{ role: "user", content: "What is the weather in Paris?" }];

async function complete() {
  const response = await fetch("https://gengen.farm/api/gengen/v1/chat/completions", {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.GENGEN_API_KEY}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({ model, messages, tools, tool_choice: "auto" }),
  });
  if (!response.ok) throw new Error(await response.text());
  return response.json();
}

let completion = await complete();
const assistant = completion.choices[0].message;
if (assistant.tool_calls?.length) {
  messages.push(assistant); // Preserve the entire message, including provider metadata.
  for (const call of assistant.tool_calls) {
    const args = JSON.parse(call.function.arguments);
    // Replace with your application's approved weather service.
    const result = call.function.name === "get_weather"
      ? { city: args.city, temperatureC: 21, source: "demo" }
      : { error: "Unknown function" };
    messages.push({ role: "tool", tool_call_id: call.id, content: JSON.stringify(result) });
  }
  completion = await complete();
}
console.log(completion.choices[0].message);

{
  "model": "gemini-3.8-flash",
  "messages": [{ "role": "user", "content": "Use Python to calculate the first 20 Fibonacci numbers." }],
  "providerOptions": {
    "google": { "tools": [{ "codeExecution": {} }] }
  }
}

{
  "model": "gemini-3.8-flash",
  "messages": [{
    "role": "user",
    "content": [
      { "type": "text", "text": "Find the search field on this page." },
      { "type": "image_url", "image_url": { "url": "data:image/png;base64,REPLACE_WITH_SCREENSHOT" } }
    ]
  }],
  "providerOptions": {
    "google": {
      "tools": [{ "computerUse": { "environment": "ENVIRONMENT_BROWSER" } }]
    }
  }
}

{
  "role": "tool",
  "tool_call_id": "RETURNED_CALL_ID",
  "content": [
    { "type": "text", "text": "{\"url\":\"https://example.com\"}" },
    { "type": "image_url", "image_url": { "url": "data:image/png;base64,REPLACE_WITH_NEW_SCREENSHOT" } }
  ]
}

{
  "model": "gemini-3.8-flash",
  "input": "What is the weather in Paris?",
  "tools": [{
    "type": "function",
    "name": "get_weather",
    "parameters": {
      "type": "object",
      "properties": { "city": { "type": "string" } },
      "required": ["city"]
    }
  }]
}