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

# tool_choice_required_unsupported

> The model does not support tool_choice: "required".

**Code**: `tool_choice_required_unsupported`
**HTTP status**: `400`
**Type**: `invalid_request`

## When it fires

Your chat request set `tool_choice: "required"`, but the selected model's `aurous_metadata.capabilities` doesn't include the `tool_choice_required` flag. The model can still call tools when `tool_choice` is `"auto"` or a specific function pin — it just can't be FORCED into a tool call.

## How to recover

Either pick a model whose capabilities include `tool_choice_required` (check `GET /v1/models`), or change your request to use `tool_choice: "auto"` and accept that the model may answer directly when it judges a tool isn't necessary.