> For the complete documentation index, see [llms.txt](https://docs.ncsa.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ncsa.ai/experimental-function-calling-json-and-regex-mode.md).

# Experimental: Function calling, JSON and Regex mode

See the support details here: <https://docs.vllm.ai/en/latest/serving/openai_compatible_server.html#extra-parameters-for-chat-api>

Note: Function calling is not supported (as of Apr 4, 2024). But very similar features are, like `guided_choice` and `guided_regex`. Together, these can re-create the abilities of function calling.

```
guided_choice: Optional[List[str]] = Field(
    description=(
    "If specified, the output will be exactly one of the choices."),
)
```