Tool Calling

Let models call your functions

Tool calling lets a model ask your application to run a function — look up an order, query a database, call a weather API — and weave the result into its answer. Token Hub forwards the standard OpenAI tools parameter to every tool-capable model in the catalog.

Defining tools

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

resp = client.chat.completions.create(
    model="glm-5-3",
    messages=[{"role": "user", "content": "Should I bring an umbrella in Lisbon?"}],
    tools=tools,
)

The tool loop

When the model wants a tool, the response's finish_reason is"tool_calls" and the message contains structured calls. You execute them, then send results back as role: "tool" messages:

python
msg = resp.choices[0].message
if msg.tool_calls:
    followup = [
        {"role": "user", "content": "Should I bring an umbrella in Lisbon?"},
        msg,
        {"role": "tool", "tool_call_id": msg.tool_calls[0].id,
         "content": '{"forecast": "light rain", "high": 18}'},
    ]
    final = client.chat.completions.create(
        model="glm-5-3", messages=followup, tools=tools)
    print(final.choices[0].message.content)

Forcing or blocking tool use

tool_choice controls behavior: "auto" (default) lets the model decide, "none" disables tools, and{"type": "function", "function": {"name": "get_weather"}}forces a specific call.

Model support

Function calling is a per-model capability — each model page lists it under Supported functionality. Programmatically, the public catalog exposes it assupports_tools. Validate tool schemas before sending: malformed definitions are the most common cause of 400 bad_request errors.