fix: Apply strict JSON schema validation in FunctionTool constructor

[habema]

Summary

Fixes an issue where directly created FunctionTool objects fail with OpenAI's Responses API due to missing additionalProperties: false in the JSON schema, while the @function_tool decorator works correctly.

Problem

The documentation example for creating FunctionTool objects directly fails with:

Error code: 400 - {'error': {'message': "Invalid schema for function 'process_user': In context=(), 'additionalProperties' is required to be supplied and to be false.", 'type': 'invalid_request_error', 'param': 'tools[0].parameters', 'code': 'invalid_function_parameters'}}

This creates an inconsistency between FunctionTool and @function_tool behavior, both of which have strict_json_schema=True by default.

Solution

• Added __post_init__ method to FunctionTool dataclass
• Automatically applies ensure_strict_json_schema() when strict_json_schema=True
• Makes behavior consistent with @function_tool decorator
• Maintains backward compatibility

Testing

The fix can be verified by running the reproduction case from the issue:

from typing import Any
from pydantic import BaseModel
from agents import RunContextWrapper, FunctionTool, Agent, Runner

class FunctionArgs(BaseModel):
    username: str
    age: int

async def run_function(ctx: RunContextWrapper[Any], args: str) -> str:
    parsed = FunctionArgs.model_validate_json(args)
    return f"{parsed.username} is {parsed.age} years old"

# This now works without manual ensure_strict_json_schema() call
tool = FunctionTool(
    name="process_user",
    description="Processes extracted user data",
    params_json_schema=FunctionArgs.model_json_schema(),
    on_invoke_tool=run_function,
)

agent = Agent(
    name="Test Agent",
    instructions="You are a test agent",
    tools=[tool]
)

result = Runner.run_sync(agent, "Process user data for John who is 30 years old")

[habema]

Linked Issue: #992

[seratch]

LGTM

[salah9003]

من هنا إلى الأعلى 👍🏿 👍🏿

[3marwanmoraly3]

From here to the top 👍🏿 👍🏿 👍🏿