# tinker_cookbook.tool_use.tools.tool

### [**tinker_cookbook.tool_use.tools.tool**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/tool_use/tools.py#L280)( _fn_)

Decorator to create a tool from a function or method.

The decorated function must return a ToolResult. Use simple_tool_result() helper for basic cases, or construct ToolResult directly for metrics/metadata.

**Usage:**
```python
@tool
async def search(query: Annotated[str, "The search query"]) -> ToolResult:
    '''Search for information.'''
    results = await do_search(query)
    return simple_tool_result(
        json.dumps({"results": results}),
        metrics={"result_count": len(results)}
    )
```

# As class method with shared state:

**class MySharedStateTools:**  
**def init(self, api_key: str):**  
    self.api_key = api_key

```python
@tool
async def search(self, query: Annotated[str, "Query"]) -> ToolResult:
    '''Search for information.'''
    results = await do_search(query, api_key=self.api_key)
    return simple_tool_result(json.dumps(results))
```

**Parameters:**

- [**fn**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/tool_use/tools.py#L280) ( _Callable[..., Any]_)

**Returns:** _[FunctionTool](https://tinker-docs.thinkingmachines.ai/cookbook/api-reference/tool_use/functiontool/)_