function_tool generates invalid schema for parameterless functions (Groq compatibility)

[robertvy]

Description

When using function_tool decorator on a function with no parameters, the generated JSON schema is rejected by Groq's API (and potentially other strict OpenAI-compatible APIs).

Error Messages

First error:

Invalid schema for function 'django_health': In context=('properties', 'kwargs'), 
schema must have a 'type' key.

After removing **kwargs:

invalid JSON schema for tool django_health, tools[4].function.parameters: 
'required' present but 'properties' is missing

Root Cause

Groq (and other strict OpenAI-compatible APIs) require this structure even for parameterless tools:

{
  "parameters": {
    "type": "object",
    "properties": {},
    "required": []
  }
}

But function_tool generates an incomplete schema missing type and/or properties when there are no parameters.

Reproduction

from livekit.agents import function_tool

@function_tool(name="health_check", description="Check system health")
async def health_check() -> str:
    return "OK"

# Use with Groq LLM - will fail with schema error

Workaround

Use the raw_schema parameter to explicitly define the schema for parameterless functions:

from livekit.agents import function_tool

async def health_check(raw_arguments: dict) -> str:
    return "OK"

raw_schema = {
    "name": "health_check",
    "description": "Check system health",
    "parameters": {
        "type": "object",
        "properties": {},
        "required": [],
    },
}

tool = function_tool(raw_schema=raw_schema)(health_check)

This bypasses the automatic schema generation and provides the exact JSON schema that Groq requires.

Note: When using raw_schema, the function receives parameters via a raw_arguments: dict parameter instead of individual arguments.

Expected Behavior

function_tool should generate valid JSON schemas for parameterless functions that work with all LLM providers, including Groq.

Environment

• livekit-agents version: latest
• LLM: Groq (via livekit.plugins.groq or OpenAI-compatible endpoint)
• Python: 3.13