> ## Documentation Index
> Fetch the complete documentation index at: https://fastmcp-docs-v3-beta2-feature-tracking.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# function_tool

# `fastmcp.tools.function_tool`

Standalone @tool decorator for FastMCP.

## Functions

### `tool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L370" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
tool(name_or_fn: str | Callable[..., Any] | None = None) -> Any
```

Standalone decorator to mark a function as an MCP tool.

Returns the original function with metadata attached. Register with a server
using mcp.add\_tool().

## Classes

### `DecoratedTool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L54" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Protocol for functions decorated with @tool.

### `ToolMeta` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L63" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Metadata attached to functions by the @tool decorator.

### `FunctionTool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L84" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

**Methods:**

#### `to_mcp_tool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L87" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
to_mcp_tool(self, **overrides: Any) -> mcp.types.Tool
```

Convert the FastMCP tool to an MCP tool.

Extends the base implementation to add task execution mode if enabled.

#### `from_function` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L106" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
from_function(cls, fn: Callable[..., Any]) -> FunctionTool
```

Create a FunctionTool from a function.

**Args:**

* `fn`: The function to wrap
* `metadata`: ToolMeta object with all configuration. If provided,
  individual parameters must not be passed.
* `name, title, etc.`: Individual parameters for backwards compatibility.
  Cannot be used together with metadata parameter.

#### `run` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L248" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
run(self, arguments: dict[str, Any]) -> ToolResult
```

Run the tool with arguments.

#### `register_with_docket` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L293" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
register_with_docket(self, docket: Docket) -> None
```

Register this tool with docket for background execution.

FunctionTool registers the underlying function, which has the user's
Depends parameters for docket to resolve.

#### `add_to_docket` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/function_tool.py#L303" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
add_to_docket(self, docket: Docket, arguments: dict[str, Any], **kwargs: Any) -> Execution
```

Schedule this tool for background execution via docket.

FunctionTool splats the arguments dict since .fn expects \*\*kwargs.

**Args:**

* `docket`: The Docket instance
* `arguments`: Tool arguments
* `fn_key`: Function lookup key in Docket registry (defaults to self.key)
* `task_key`: Redis storage key for the result
* `**kwargs`: Additional kwargs passed to docket.add()