content: """Example showing direct CallToolResult return for advanced control."""
  
  from typing import Annotated
  
  from pydantic import BaseModel
  
  from mcp.server.fastmcp import FastMCP
  from mcp.types import CallToolResult, TextContent
  
  mcp = FastMCP("CallToolResult Example")
  
  
  class ValidationModel(BaseModel):
      """Model for validating structured output."""
  
      status: str
      data: dict[str, int]
  
  
  @mcp.tool()
  def advanced_tool() -> CallToolResult:
      """Return CallToolResult directly for full control including _meta field."""
      return CallToolResult(
          content=[TextContent(type="text", text="Response visible to the model")],
          _meta={"hidden": "data for client applications only"},
      )
  
  
  @mcp.tool()
  def validated_tool() -> Annotated[CallToolResult, ValidationModel]:
      """Return CallToolResult with structured output validation."""
      return CallToolResult(
          content=[TextContent(type="text", text="Validated response")],
          structuredContent={"status": "success", "data": {"result": 42}},
          _meta={"internal": "metadata"},
      )
  
  
  @mcp.tool()
  def empty_result_tool() -> CallToolResult:
      """For empty results, return CallToolResult with empty content."""
      return CallToolResult(content=[])
  