> ## 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.
# tool
# `fastmcp.tools.tool`
## Functions
### `default_serializer`
```python theme={null}
default_serializer(data: Any) -> str
```
## Classes
### `ToolResult`
**Methods:**
#### `to_mcp_result`
```python theme={null}
to_mcp_result(self) -> list[ContentBlock] | tuple[list[ContentBlock], dict[str, Any]] | CallToolResult
```
### `Tool`
Internal tool registration info.
**Methods:**
#### `to_mcp_tool`
```python theme={null}
to_mcp_tool(self, **overrides: Any) -> MCPTool
```
Convert the FastMCP tool to an MCP tool.
#### `from_function`
```python theme={null}
from_function(cls, fn: Callable[..., Any]) -> FunctionTool
```
Create a Tool from a function.
#### `run`
```python theme={null}
run(self, arguments: dict[str, Any]) -> ToolResult
```
Run the tool with arguments.
This method is not implemented in the base Tool class and must be
implemented by subclasses.
`run()` can EITHER return a list of ContentBlocks, or a tuple of
(list of ContentBlocks, dict of structured output).
#### `convert_result`
```python theme={null}
convert_result(self, raw_value: Any) -> ToolResult
```
Convert a raw result to ToolResult.
Handles ToolResult passthrough and converts raw values using the tool's
attributes (serializer, output\_schema) for proper conversion.
#### `register_with_docket`
```python theme={null}
register_with_docket(self, docket: Docket) -> None
```
Register this tool with docket for background execution.
#### `add_to_docket`
```python theme={null}
add_to_docket(self, docket: Docket, arguments: dict[str, Any], **kwargs: Any) -> Execution
```
Schedule this tool for background execution via docket.
**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()
#### `from_tool`
```python theme={null}
from_tool(cls, tool: Tool) -> TransformedTool
```
#### `get_span_attributes`
```python theme={null}
get_span_attributes(self) -> dict[str, Any]
```