LocalAI/docs/content/features/openai-functions.md

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![Function calling: one tool-call request shape, each backend's native parser extracts the calls](/images/diagrams/tool-call-parsers.png)

LocalAI supports running the OpenAI [functions and tools API](https://platform.openai.com/docs/api-reference/chat/create#chat-create-tools) across multiple backends. The OpenAI request shape is the same regardless of which backend runs your model — LocalAI is responsible for extracting structured tool calls from the model's output before returning the response.

![localai-functions-1](https://github.com/ggerganov/llama.cpp/assets/2420543/5bd15da2-78c1-4625-be90-1e938e6823f1)

To learn more about OpenAI functions, see also the [OpenAI API blog post](https://openai.com/blog/function-calling-and-other-api-updates).

LocalAI also supports [JSON mode](https://platform.openai.com/docs/guides/text-generation/json-mode) out of the box on llama.cpp-compatible models.

💡 Check out [LocalAGI](https://github.com/mudler/LocalAGI) for an example on how to use LocalAI functions.

## Supported backends

| Backend | How tool calls are extracted |
|---------|------------------------------|
| `llama.cpp` | C++ incremental parser; any `ggml`/`gguf` model works out of the box, no configuration needed |
| `vllm` | vLLM's native `ToolParserManager` — select a parser with `tool_parser:<name>` in the model `options`. Auto-set by the gallery importer for known families |
| `vllm-omni` | Same as vLLM |
| `mlx` | `mlx_lm.tool_parsers` — **auto-detected from the chat template**, no configuration needed |
| `mlx-vlm` | `mlx_vlm.tool_parsers` (with fallback to mlx-lm parsers) — **auto-detected from the chat template**, no configuration needed |

Reasoning content (`<think>...</think>` blocks from DeepSeek R1, Qwen3, Gemma 4, etc.) is returned in the OpenAI `reasoning_content` field on the same backends.

## Setup

### llama.cpp

No configuration required — the autoparser detects the tool call format for any `ggml`/`gguf` model that was trained with tool support.

### vLLM / vLLM Omni

The parser must be specified explicitly because vLLM itself doesn't auto-detect one. Pass it via the model `options`:

```yaml
name: qwen3-8b
backend: vllm
parameters:
  model: Qwen/Qwen3-8B
options:
  - tool_parser:hermes
  - reasoning_parser:qwen3
template:
  use_tokenizer_template: true
```

When you import a vLLM model through the LocalAI gallery, the importer looks up the model family and pre-fills `tool_parser:` and `reasoning_parser:` for you — you only need to override them for non-standard model names.

Available tool parsers include `hermes`, `llama3_json`, `llama4_pythonic`, `mistral`, `qwen3_xml`, `deepseek_v3`, `granite4`, `kimi_k2`, `glm45`, and more. Available reasoning parsers include `deepseek_r1`, `qwen3`, `mistral`, `gemma4`, `granite`. See the upstream vLLM documentation for the full list.

### MLX / MLX-VLM

MLX backends **auto-detect** the right tool parser by inspecting the model's chat template — you don't need to set anything. Just load an MLX-quantized model that was trained with tool support:

```yaml
name: qwen2.5-0.5b-mlx
backend: mlx
parameters:
  model: mlx-community/Qwen2.5-0.5B-Instruct-4bit
template:
  use_tokenizer_template: true
```

The gallery importer will still append `tool_parser:` and `reasoning_parser:` entries to the YAML for visibility and consistency with the other backends, but those are informational — the runtime auto-detection in the MLX backend ignores them and uses the parser matched to the chat template.

Supported parser families: `hermes`/`json_tools`, `mistral`, `gemma4`, `glm47`, `kimi_k2`, `longcat`, `minimax_m2`, `pythonic`, `qwen3_coder`, `function_gemma`.


## Usage example

You can configure a model manually with a YAML config file in the models directory, for example:

```yaml
name: gpt-3.5-turbo
parameters:
  # Model file name
  model: ggml-openllama.bin
  top_p: 80
  top_k: 0.9
  temperature: 0.1
```

To use the functions with the OpenAI client in python:

```python
from openai import OpenAI

messages = [{"role": "user", "content": "What is the weather like in Beijing now?"}]
tools = [
    {
        "type": "function",
        "function": {
            "name": "get_current_weather",
            "description": "Return the temperature of the specified region specified by the user",
            "parameters": {
                "type": "object",
                "properties": {
                    "location": {
                        "type": "string",
                        "description": "User specified region",
                    },
                    "unit": {
                        "type": "string",
                        "enum": ["celsius", "fahrenheit"],
                        "description": "temperature unit"
                    },
                },
                "required": ["location"],
            },
        },
    }
]

client = OpenAI(
    # This is the default and can be omitted
    api_key="test",
    base_url="http://localhost:8080/v1/"
)

response =client.chat.completions.create(
    messages=messages,
    tools=tools,
    tool_choice ="auto",
    model="gpt-4",
)
#...
```

For example, with curl:

```bash
curl http://localhost:8080/v1/chat/completions -H "Content-Type: application/json" -d '{
  "model": "gpt-4",
  "messages": [{"role": "user", "content": "What is the weather like in Beijing now?"}],
  "tools": [
        {
            "type": "function",
            "function": {
                "name": "get_current_weather",
                "description": "Return the temperature of the specified region specified by the user",
                "parameters": {
                    "type": "object",
                    "properties": {
                        "location": {
                            "type": "string",
                            "description": "User specified region"
                        },
                        "unit": {
                            "type": "string",
                            "enum": ["celsius", "fahrenheit"],
                            "description": "temperature unit"
                        }
                    },
                    "required": ["location"]
                }
            }
        }
    ],
    "tool_choice":"auto"
}'
```

Return data：

```json
{
    "created": 1724210813,
    "object": "chat.completion",
    "id": "16b57014-477c-4e6b-8d25-aad028a5625e",
    "model": "gpt-4",
    "choices": [
        {
            "index": 0,
            "finish_reason": "tool_calls",
            "message": {
                "role": "assistant",
                "content": "",
                "tool_calls": [
                    {
                        "index": 0,
                        "id": "16b57014-477c-4e6b-8d25-aad028a5625e",
                        "type": "function",
                        "function": {
                            "name": "get_current_weather",
                            "arguments": "{\"location\":\"Beijing\",\"unit\":\"celsius\"}"
                        }
                    }
                ]
            }
        }
    ],
    "usage": {
        "prompt_tokens": 221,
        "completion_tokens": 26,
        "total_tokens": 247
    }
}
```

## Advanced

### Use functions without grammars

The functions calls maps automatically to grammars which are currently supported only by llama.cpp, however, it is possible to turn off the use of grammars, and extract tool arguments from the LLM responses, by specifying in the YAML file `no_grammar` and a regex to map the response from the LLM:

```yaml
name: model_name
parameters:
  # Model file name
  model: model/name

function:
  # set to true to not use grammars
  no_grammar: true
  # set one or more regexes used to extract the function tool arguments from the LLM response
  response_regex:
  - "(?P<function>\w+)\s*\((?P<arguments>.*)\)"
```

The response regex have to be a regex with named parameters to allow to scan the function name and the arguments. For instance, consider:

```
(?P<function>\w+)\s*\((?P<arguments>.*)\)
```

will catch

```
function_name({ "foo": "bar"})
```

### Parallel tools calls

This feature is experimental and has to be configured in the YAML of the model by enabling `function.parallel_calls`:

```yaml
name: gpt-3.5-turbo
parameters:
  # Model file name
  model: ggml-openllama.bin
  top_p: 80
  top_k: 0.9
  temperature: 0.1

function:
  # set to true to allow the model to call multiple functions in parallel
  parallel_calls: true
```

### Use functions with grammar

It is possible to also specify the full function signature (for debugging, or to use with other clients).

The chat endpoint accepts the `grammar_json_functions` additional parameter which takes a JSON schema object.

For example, with curl:

```bash
curl http://localhost:8080/v1/chat/completions -H "Content-Type: application/json" -d '{
     "model": "gpt-4",
     "messages": [{"role": "user", "content": "How are you?"}],
     "temperature": 0.1,
     "grammar_json_functions": {
        "oneOf": [
            {
                "type": "object",
                "properties": {
                    "function": {"const": "create_event"},
                    "arguments": {
                        "type": "object",
                        "properties": {
                            "title": {"type": "string"},
                            "date": {"type": "string"},
                            "time": {"type": "string"}
                        }
                    }
                }
            },
            {
                "type": "object",
                "properties": {
                    "function": {"const": "search"},
                    "arguments": {
                        "type": "object",
                        "properties": {
                            "query": {"type": "string"}
                        }
                    }
                }
            }
        ]
    }
   }'
```

Grammars and function tools can be used as well in conjunction with vision APIs:

```bash
 curl http://localhost:8080/v1/chat/completions -H "Content-Type: application/json" -d '{
     "model": "llava", "grammar": "root ::= (\"yes\" | \"no\")",
     "messages": [{"role": "user", "content": [{"type":"text", "text": "Is there some grass in the image?"}, {"type": "image_url", "image_url": {"url": "https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg" }}], "temperature": 0.9}]}'
```


## 💡 Examples

A full e2e example with `docker-compose` is available [here](https://github.com/mudler/LocalAI-examples/tree/main/functions).