---
title: tool
sidebarTitle: tool
---
# `fastmcp.tools.tool`
## Functions
### `default_serializer`
```python
default_serializer(data: Any) -> str
```
## Classes
### `ToolResult`
**Methods:**
#### `to_mcp_result`
```python
to_mcp_result(self) -> list[ContentBlock] | tuple[list[ContentBlock], dict[str, Any]] | CallToolResult
```
### `Tool`
Internal tool registration info.
**Methods:**
#### `to_mcp_tool`
```python
to_mcp_tool(self, **overrides: Any) -> MCPTool
```
Convert the FastMCP tool to an MCP tool.
#### `from_function`
```python
from_function(fn: Callable[..., Any], name: str | None = None, title: str | None = None, description: str | None = None, icons: list[Icon] | None = None, tags: set[str] | None = None, annotations: ToolAnnotations | None = None, exclude_args: list[str] | None = None, output_schema: dict[str, Any] | NotSetT | None = NotSet, serializer: ToolResultSerializerType | None = None, meta: dict[str, Any] | None = None, task: bool | TaskConfig | None = None) -> FunctionTool
```
Create a Tool from a function.
#### `run`
```python
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
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
register_with_docket(self, docket: Docket) -> None
```
Register this tool with docket for background execution.
#### `add_to_docket`
```python
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
from_tool(cls, tool: Tool) -> TransformedTool
```
### `FunctionTool`
**Methods:**
#### `to_mcp_tool`
```python
to_mcp_tool(self, **overrides: Any) -> MCPTool
```
Convert the FastMCP tool to an MCP tool.
Extends the base implementation to add task execution mode if enabled.
#### `from_function`
```python
from_function(cls, fn: Callable[..., Any], name: str | None = None, title: str | None = None, description: str | None = None, icons: list[Icon] | None = None, tags: set[str] | None = None, annotations: ToolAnnotations | None = None, exclude_args: list[str] | None = None, output_schema: dict[str, Any] | NotSetT | None = NotSet, serializer: ToolResultSerializerType | None = None, meta: dict[str, Any] | None = None, task: bool | TaskConfig | None = None) -> FunctionTool
```
Create a Tool from a function.
#### `run`
```python
run(self, arguments: dict[str, Any]) -> ToolResult
```
Run the tool with arguments.
#### `register_with_docket`
```python
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`
```python
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()
### `ParsedFunction`
**Methods:**
#### `from_function`
```python
from_function(cls, fn: Callable[..., Any], exclude_args: list[str] | None = None, validate: bool = True, wrap_non_object_output_schema: bool = True) -> ParsedFunction
```