Tool Calling · Docs

Models marked Tool calling in Models accept OpenAI-format tools.

tools = [{
    "type": "function",
    "function": {
        "name": "get_weather",
        "description": "Current weather for a city",
        "parameters": {
            "type": "object",
            "properties": {"city": {"type": "string"}},
            "required": ["city"],
        },
    },
}]

messages = [{"role": "user", "content": "Is it raining in Singapore?"}]
first = client.chat.completions.create(model="zai-org/GLM-5.3", messages=messages, tools=tools)
call = first.choices[0].message.tool_calls[0]

messages.append(first.choices[0].message)
messages.append({"role": "tool", "tool_call_id": call.id, "content": '{"raining": true, "temp_c": 27}'})

final = client.chat.completions.create(model="zai-org/GLM-5.3", messages=messages, tools=tools)
print(final.choices[0].message.content)

`tool_choice`

Value	Behavior
`"auto"` (default)	The model decides whether to call a tool
`"none"`	Never call a tool
`"required"`	Must call at least one tool, where the model supports it
`{"type": "function", "function": {"name": "…"}}`	Force a specific tool, where the model supports it

Tips

Keep tool descriptions short and specific; the model reads them as part of the prompt (and you pay for those tokens).
Validate tool arguments before executing them — they’re generated text.
For many parallel calls, check parallel_tool_calls support per model in models.json.