Unit Converter MCP

Instructions

Implementation Reference

• src/unit_converter_mcp/server.py:215-229 (handler)

  MCP tool handler for 'convert_mass'. Registers the tool via @app.tool() decorator and handles the execution by calling the underlying convert_mass_tool, formatting input/output as a dict.

  @app.tool()
  def convert_mass(
      value: Annotated[float, Field(description="Weight value to convert")],
      from_unit: Annotated[MASS_UNIT, Field(description="Source unit")],
      to_unit: Annotated[MASS_UNIT, Field(description="Target unit")],
  ) -> dict:
      """Convert weight between units."""
      converted_value = convert_mass_tool(value, from_unit, to_unit)
      return {
          "original_value": value,
          "original_unit": from_unit,
          "converted_value": converted_value,
          "converted_unit": to_unit,
          "conversion_type": "mass",
      }

• src/unit_converter_mcp/tools/mass.py:29-61 (helper)

  Core helper function implementing the mass unit conversion logic by converting to kilograms as intermediate unit.

  def convert_mass_tool(
      value: float,
      from_unit: MASS_UNIT,
      to_unit: MASS_UNIT,
  ) -> float:
      """Convert mass between units."""
  
      # Convert to kilograms first
      to_kilograms = {
          "carat": 0.0002,
          "decagram": 0.01,
          "hectogram": 0.1,
          "gram": 0.001,
          "milligram": 1e-6,
          "microgram": 1e-9,
          "nanogram": 1e-12,
          "picogram": 1e-15,
          "femtogram": 1e-18,
          "grain": 6.479891e-05,
          "ounce": 0.028349523125,
          "troy ounce": 0.0311034768,
          "pound": 0.45359237,
          "stone": 6.35029318,
          "short ton (US)": 907.18474,
          "long ton (UK)": 1_016.0469088,
          "tonne": 1_000.0,
          "kilotonne": 1_000_000.0,
          "megatonne": 1_000_000_000.0,
          "kilogram": 1.0,
      }
  
      kg = value * to_kilograms[from_unit]
      return kg / to_kilograms[to_unit]

• src/unit_converter_mcp/tools/mass.py:5-26 (schema)

  Type definition for supported mass units, used in tool schema validation.

  MASS_UNIT = Literal[
      "carat",
      "decagram",
      "hectogram",
      "gram",
      "milligram",
      "microgram",
      "nanogram",
      "picogram",
      "femtogram",
      "grain",
      "ounce",
      "troy ounce",
      "pound",
      "stone",
      "short ton (US)",
      "long ton (UK)",
      "tonne",
      "kilotonne",
      "megatonne",
      "kilogram",
  ]