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fastmcp.tools.tool

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Functions

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default_serializer 

default_serializer(data: Any) -> str

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Classes

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ToolResult

Methods:

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to_mcp_result 

to_mcp_result(self) -> list[ContentBlock] | tuple[list[ContentBlock], dict[str, Any]] | CallToolResult

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Tool

Internal tool registration info. Methods:

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to_mcp_tool 

to_mcp_tool(self, **overrides: Any) -> MCPTool
Convert the FastMCP tool to an MCP tool.

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from_function 

from_function(cls, fn: Callable[..., Any]) -> FunctionTool
Create a Tool from a function.

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run 

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).

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convert_result 

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.

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register_with_docket 

register_with_docket(self, docket: Docket) -> None
Register this tool with docket for background execution.

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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. 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()

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from_tool 

from_tool(cls, tool: Tool) -> TransformedTool

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get_span_attributes 

get_span_attributes(self) -> dict[str, Any]