Merge pull request #137 from modelcontextprotocol/v1.2.x

fix: #129 resource template handling in FastMCP server

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)

src/mcp/cli/cli.py

@@ -6,10 +6,10 @@
 import subprocess
 import sys
 from pathlib import Path
+from typing import Annotated
 
 try:
     import typer
-    from typing_extensions import Annotated
 except ImportError:
     print("Error: typer is required. Install with 'pip install mcp[cli]'")
     sys.exit(1)

src/mcp/server/fastmcp/server.py

@@ -133,8 +133,7 @@ def _setup_handlers(self) -> None:
         self._mcp_server.read_resource()(self.read_resource)
         self._mcp_server.list_prompts()(self.list_prompts)
         self._mcp_server.get_prompt()(self.get_prompt)
-        # TODO: This has not been added to MCP yet, see https://github.com/jlowin/fastmcp/issues/10
-        # self._mcp_server.list_resource_templates()(self.list_resource_templates)
+        self._mcp_server.list_resource_templates()(self.list_resource_templates)
 
     async def list_tools(self) -> list[MCPTool]:
         """List all available tools."""

tests/issues/test_129_resource_templates.py

@@ -0,0 +1,44 @@
+import pytest
+
+from mcp import types
+from mcp.server.fastmcp import FastMCP
+
+
+@pytest.mark.anyio
+async def test_resource_templates():
+    # Create an MCP server
+    mcp = FastMCP("Demo")
+
+    # Add a dynamic greeting resource
+    @mcp.resource("greeting://{name}")
+    def get_greeting(name: str) -> str:
+        """Get a personalized greeting"""
+        return f"Hello, {name}!"
+
+    @mcp.resource("users://{user_id}/profile")
+    def get_user_profile(user_id: str) -> str:
+        """Dynamic user data"""
+        return f"Profile data for user {user_id}"
+
+    # Get the list of resource templates using the underlying server
+    # Note: list_resource_templates() returns a decorator that wraps the handler
+    # The handler returns a ServerResult with a ListResourceTemplatesResult inside
+    result = await mcp._mcp_server.request_handlers[types.ListResourceTemplatesRequest](
+        types.ListResourceTemplatesRequest(
+            method="resources/templates/list", params=None, cursor=None
+        )
+    )
+    assert isinstance(result.root, types.ListResourceTemplatesResult)
+    templates = result.root.resourceTemplates
+
+    # Verify we get both templates back
+    assert len(templates) == 2
+
+    # Verify template details
+    greeting_template = next(t for t in templates if t.name == "get_greeting")
+    assert greeting_template.uriTemplate == "greeting://{name}"
+    assert greeting_template.description == "Get a personalized greeting"
+
+    profile_template = next(t for t in templates if t.name == "get_user_profile")
+    assert profile_template.uriTemplate == "users://{user_id}/profile"
+    assert profile_template.description == "Dynamic user data"

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"