feat: add example and test for parameter descriptions in FastMCP tools

Author: dsp-ant

examples/fastmcp/parameter_descriptions.py

@@ -0,0 +1,21 @@
+"""
+FastMCP Example showing parameter descriptions
+"""
+
+from pydantic import Field
+
+from mcp.server.fastmcp import FastMCP
+
+# Create server
+mcp = FastMCP("Parameter Descriptions Server")
+
+
+@mcp.tool()
+def greet_user(
+    name: str = Field(description="The name of the person to greet"),
+    title: str = Field(description="Optional title like Mr/Ms/Dr", default=""),
+    times: int = Field(description="Number of times to repeat the greeting", default=1),
+) -> str:
+    """Greet a user with optional title and repetition"""
+    greeting = f"Hello {title + ' ' if title else ''}{name}!"
+    return "\n".join([greeting] * times)

tests/server/fastmcp/test_parameter_descriptions.py

@@ -0,0 +1,30 @@
+"""Test that parameter descriptions are properly exposed through list_tools"""
+
+import pytest
+from pydantic import Field
+
+from mcp.server.fastmcp import FastMCP
+
+
+@pytest.mark.asyncio
+async def test_parameter_descriptions():
+    mcp = FastMCP("Test Server")
+
+    @mcp.tool()
+    def greet(
+        name: str = Field(description="The name to greet"),
+        title: str = Field(description="Optional title", default=""),
+    ) -> str:
+        """A greeting tool"""
+        return f"Hello {title} {name}"
+
+    tools = await mcp.list_tools()
+    assert len(tools) == 1
+    tool = tools[0]
+
+    # Check that parameter descriptions are present in the schema
+    properties = tool.inputSchema["properties"]
+    assert "name" in properties
+    assert properties["name"]["description"] == "The name to greet"
+    assert "title" in properties
+    assert properties["title"]["description"] == "Optional title"