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fastmcp.tools.function_tool

Standalone @tool decorator for FastMCP.

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Functions

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tool 

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().

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Classes

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DecoratedTool

Protocol for functions decorated with @tool.

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ToolMeta

Metadata attached to functions by the @tool decorator.

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FunctionTool

Methods:

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to_mcp_tool 

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.

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from_function 

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.

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run 

run(self, arguments: dict[str, Any]) -> ToolResult
Run the tool with arguments.

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register_with_docket 

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.

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add_to_docket 

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()