Server initialize response update to last spec (add title, description) (#1634)

Author: yannj-fr

src/mcp/server/fastmcp/server.py

@@ -147,9 +147,12 @@ class FastMCP(Generic[LifespanResultT]):
     def __init__(  # noqa: PLR0913
         self,
         name: str | None = None,
+        title: str | None = None,
+        description: str | None = None,
         instructions: str | None = None,
         website_url: str | None = None,
         icons: list[Icon] | None = None,
+        version: str | None = None,
         auth_server_provider: (OAuthAuthorizationServerProvider[Any, Any, Any] | None) = None,
         token_verifier: TokenVerifier | None = None,
         event_store: EventStore | None = None,
@@ -204,9 +207,12 @@ def __init__(  # noqa: PLR0913
 
         self._mcp_server = MCPServer(
             name=name or "FastMCP",
+            title=title,
+            description=description,
             instructions=instructions,
             website_url=website_url,
             icons=icons,
+            version=version,
             # TODO(Marcelo): It seems there's a type mismatch between the lifespan type from an FastMCP and Server.
             # We need to create a Lifespan type that is a generic on the server type, like Starlette does.
             lifespan=(lifespan_wrapper(self, self.settings.lifespan) if self.settings.lifespan else default_lifespan),  # type: ignore
@@ -245,6 +251,14 @@ def __init__(  # noqa: PLR0913
     def name(self) -> str:
         return self._mcp_server.name
 
+    @property
+    def title(self) -> str | None:
+        return self._mcp_server.title
+
+    @property
+    def description(self) -> str | None:
+        return self._mcp_server.description
+
     @property
     def instructions(self) -> str | None:
         return self._mcp_server.instructions
@@ -257,6 +271,10 @@ def website_url(self) -> str | None:
     def icons(self) -> list[Icon] | None:
         return self._mcp_server.icons
 
+    @property
+    def version(self) -> str | None:
+        return self._mcp_server.version
+
     @property
     def session_manager(self) -> StreamableHTTPSessionManager:
         """Get the StreamableHTTP session manager.

src/mcp/server/lowlevel/server.py

@@ -139,6 +139,8 @@ def __init__(
         self,
         name: str,
         version: str | None = None,
+        title: str | None = None,
+        description: str | None = None,
         instructions: str | None = None,
         website_url: str | None = None,
         icons: list[types.Icon] | None = None,
@@ -149,6 +151,8 @@ def __init__(
     ):
         self.name = name
         self.version = version
+        self.title = title
+        self.description = description
         self.instructions = instructions
         self.website_url = website_url
         self.icons = icons
@@ -181,6 +185,8 @@ def pkg_version(package: str) -> str:
         return InitializationOptions(
             server_name=self.name,
             server_version=self.version if self.version else pkg_version("mcp"),
+            title=self.title,
+            description=self.description,
             capabilities=self.get_capabilities(
                 notification_options or NotificationOptions(),
                 experimental_capabilities or {},

src/mcp/server/models.py

@@ -14,6 +14,8 @@
 class InitializationOptions(BaseModel):
     server_name: str
     server_version: str
+    title: str | None = None
+    description: str | None = None
     capabilities: ServerCapabilities
     instructions: str | None = None
     website_url: str | None = None

src/mcp/server/session.py

@@ -178,6 +178,8 @@ async def _received_request(self, responder: RequestResponder[types.ClientReques
                                 capabilities=self._init_options.capabilities,
                                 serverInfo=types.Implementation(
                                     name=self._init_options.server_name,
+                                    title=self._init_options.title,
+                                    description=self._init_options.description,
                                     version=self._init_options.server_version,
                                     websiteUrl=self._init_options.website_url,
                                     icons=self._init_options.icons,

src/mcp/types.py

@@ -249,6 +249,12 @@ class Implementation(BaseMetadata):
 
     version: str
 
+    title: str | None = None
+    """An optional human-readable title for this implementation."""
+
+    description: str | None = None
+    """An optional human-readable description of what this implementation does."""
+
     websiteUrl: str | None = None
     """An optional URL of the website for this implementation."""
 

tests/server/fastmcp/test_server.py

@@ -20,6 +20,7 @@
     BlobResourceContents,
     ContentBlock,
     EmbeddedResource,
+    Icon,
     ImageContent,
     TextContent,
     TextResourceContents,
@@ -29,9 +30,23 @@
 class TestServer:
     @pytest.mark.anyio
     async def test_create_server(self):
-        mcp = FastMCP(instructions="Server instructions")
+        mcp = FastMCP(
+            title="FastMCP Server",
+            description="Server description",
+            instructions="Server instructions",
+            website_url="https://example.com/mcp_server",
+            version="1.0",
+            icons=[Icon(src="https://example.com/icon.png", mimeType="image/png", sizes=["48x48", "96x96"])],
+        )
         assert mcp.name == "FastMCP"
+        assert mcp.title == "FastMCP Server"
+        assert mcp.description == "Server description"
         assert mcp.instructions == "Server instructions"
+        assert mcp.website_url == "https://example.com/mcp_server"
+        assert mcp.version == "1.0"
+        assert isinstance(mcp.icons, list)
+        assert len(mcp.icons) == 1
+        assert mcp.icons[0].src == "https://example.com/icon.png"
 
     @pytest.mark.anyio
     async def test_normalize_path(self):

tests/server/fastmcp/test_title.py

@@ -10,6 +10,29 @@
 from mcp.types import Prompt, Resource, ResourceTemplate, Tool, ToolAnnotations
 
 
+@pytest.mark.anyio
+async def test_server_name_title_description_version():
+    """Test that server title and description are set and retrievable correctly."""
+    mcp = FastMCP(
+        name="TestServer",
+        title="Test Server Title",
+        description="This is a test server description.",
+        version="1.0",
+    )
+
+    assert mcp.title == "Test Server Title"
+    assert mcp.description == "This is a test server description."
+    assert mcp.version == "1.0"
+
+    # Start server and connect client
+    async with create_connected_server_and_client_session(mcp._mcp_server) as client:
+        init_result = await client.initialize()
+        assert init_result.serverInfo.name == "TestServer"
+        assert init_result.serverInfo.title == "Test Server Title"
+        assert init_result.serverInfo.description == "This is a test server description."
+        assert init_result.serverInfo.version == "1.0"
+
+
 @pytest.mark.anyio
 async def test_tool_title_precedence():
     """Test that tool title precedence works correctly: title > annotations.title > name."""