---
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#L75" 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#L79" 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#L124" 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#L140" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Internal tool registration info.


**Methods:**

#### `to_mcp_tool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L172" 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#L201" 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, task: bool | TaskConfig | 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#L231" 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).


#### `convert_result` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L243" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```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` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L335" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
register_with_docket(self, docket: Docket) -> None
```

Register this tool with docket for background execution.


#### `add_to_docket` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L341" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```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` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L365" 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#L397" 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/tool.py#L400" 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.

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/tool.py#L423" 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, task: bool | TaskConfig | 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#L501" 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.


#### `register_with_docket` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L511" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```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` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L521" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```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` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L563" 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#L571" 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
```
