> ## Documentation Index
> Fetch the complete documentation index at: https://docs.tera.gw/llms.txt
> Use this file to discover all available pages before exploring further.

# Tool calling

> OpenAI-compatible function calling.

Tera supports tool calling on models that advertise the `tools` feature in their [catalog entry](/api-reference/models). The request and response shapes match the OpenAI Chat Completions API.

## Defining tools

```python theme={null}
from openai import OpenAI

client = OpenAI(base_url="https://api.tera.gw/v1", api_key="sk-tera-...")

tools = [
    {
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Get current weather in a city",
            "parameters": {
                "type": "object",
                "properties": {
                    "city": {"type": "string", "description": "City name"},
                    "unit": {"type": "string", "enum": ["celsius", "fahrenheit"]}
                },
                "required": ["city"]
            }
        }
    }
]

resp = client.chat.completions.create(
    model="Qwen/Qwen2.5-7B-Instruct",
    messages=[{"role": "user", "content": "What's the weather in Paris?"}],
    tools=tools,
)

print(resp.choices[0].message.tool_calls)
```

## Response

When the model decides to call a tool, the response carries `tool_calls` and `finish_reason: "tool_calls"`:

```json theme={null}
{
  "choices": [
    {
      "message": {
        "role": "assistant",
        "content": null,
        "tool_calls": [
          {
            "id": "call_abc123",
            "type": "function",
            "function": {
              "name": "get_weather",
              "arguments": "{\"city\":\"Paris\",\"unit\":\"celsius\"}"
            }
          }
        ]
      },
      "finish_reason": "tool_calls"
    }
  ]
}
```

## Returning tool results

Append the assistant's tool call and your tool's output to `messages`, then call the API again:

```python theme={null}
messages = [
    {"role": "user", "content": "What's the weather in Paris?"},
    resp.choices[0].message,  # the assistant tool call
    {
        "role": "tool",
        "tool_call_id": "call_abc123",
        "content": "18C, partly cloudy"
    }
]

final = client.chat.completions.create(
    model="Qwen/Qwen2.5-7B-Instruct",
    messages=messages,
    tools=tools,
)
print(final.choices[0].message.content)
```

## `tool_choice`

Default is `"auto"` — the model decides whether to call a tool. Other modes:

* `"none"` — disable tool calling for this request
* `"required"` — force a tool call
* `{"type": "function", "function": {"name": "..."}}` — force a specific tool

## Streaming tool calls

With `stream: true`, tool call arguments arrive as deltas. Concatenate `delta.tool_calls[i].function.arguments` strings across chunks to reconstruct the full JSON.

## Model support

Not every model in our catalog supports tools. Check `supported_features` in `/v1/models` — only models that include `"tools"` will reliably call functions. See [Models](/models/overview).