fastmcp/docs/python-sdk/fastmcp-tools-tool.mdx
2025-12-01 13:51:48 -05:00

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---
title: tool
sidebarTitle: tool
---
# `fastmcp.tools.tool`
## Functions
### `default_serializer` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L60" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
default_serializer(data: Any) -> str
```
## Classes
### `ToolResult` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L64" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
**Methods:**
#### `to_mcp_result` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L97" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
to_mcp_result(self) -> list[ContentBlock] | tuple[list[ContentBlock], dict[str, Any]] | CallToolResult
```
### `Tool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L113" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
Internal tool registration info.
**Methods:**
#### `enable` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L131" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
enable(self) -> None
```
#### `disable` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L139" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
disable(self) -> None
```
#### `to_mcp_tool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L147" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
to_mcp_tool(self, **overrides: Any) -> MCPTool
```
Convert the FastMCP tool to an MCP tool.
#### `from_function` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L175" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```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, enabled: bool | None = None) -> FunctionTool
```
Create a Tool from a function.
#### `run` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L205" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```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).
#### `from_tool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L218" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
from_tool(cls, tool: Tool) -> TransformedTool
```
### `FunctionTool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L252" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
**Methods:**
#### `from_function` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L256" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```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, enabled: bool | None = None) -> FunctionTool
```
Create a Tool from a function.
#### `run` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L318" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
run(self, arguments: dict[str, Any]) -> ToolResult
```
Run the tool with arguments.
### `ParsedFunction` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L385" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
**Methods:**
#### `from_function` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L393" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
from_function(cls, fn: Callable[..., Any], exclude_args: list[str] | None = None, validate: bool = True, wrap_non_object_output_schema: bool = True) -> ParsedFunction
```