# Tools

Your application executes tool calls and returns their results.

## Define a function

Add `tools` to a `POST /v1/chat/completions` request using the
[quickstart](/guides/inference/) setup:

```json
{
  "tools": [
    {
      "type": "function",
      "function": {
        "name": "get_weather",
        "description": "Get the current weather in a city.",
        "parameters": {
          "type": "object",
          "properties": {"city": {"type": "string"}},
          "required": ["city"]
        }
      }
    }
  ],
  "tool_choice": "auto"
}
```

The model can answer directly or return `message.tool_calls`. To require this
function, set `tool_choice` to
`{"type": "function", "function": {"name": "get_weather"}}`.

## Return the result

Append the assistant message, validate and execute each tool call, then append
one result per call:

```json
{
  "role": "tool",
  "tool_call_id": "<id-from-tool_calls>",
  "content": "<your-function-result>"
}
```

Resend the conversation with the same tools. For streaming, assemble all
argument fragments before parsing or executing a call.