feat(mcpserver): expose public get_tool(name) on MCPServer

Add MCPServer.get_tool to retrieve a registered tool by name without
using the private _tool_manager, completing the add/remove CRUD surface.

Fixes #3162

Author: arimu1

src/mcp/server/mcpserver/server.py

@@ -607,6 +607,20 @@ def add_tool(
             structured_output=structured_output,
         )
 
+    def get_tool(self, name: str) -> Tool | None:
+        """Get a registered tool by name.
+
+        Returns the tool registration (including its mutable `parameters` JSON schema)
+        so callers can inspect or update a tool without reaching into `_tool_manager`.
+
+        Args:
+            name: The name of the tool to look up
+
+        Returns:
+            The registered tool, or `None` if no tool with that name exists
+        """
+        return self._tool_manager.get_tool(name)
+
     def remove_tool(self, name: str) -> None:
         """Remove a tool from the server by name.
 

tests/server/mcpserver/test_server.py

@@ -2348,6 +2348,39 @@ def greeting() -> str:  # pragma: no cover
         mcp.remove_prompt("greeting")
 
 
+def test_get_tool_returns_registered_tool_or_none() -> None:
+    """SDK-defined: public get_tool completes add/remove without using _tool_manager."""
+    mcp = MCPServer()
+
+    def echo(text: str) -> str:  # pragma: no cover
+        return text
+
+    mcp.add_tool(echo)
+    tool = mcp.get_tool("echo")
+    assert tool is not None
+    assert tool.name == "echo"
+    assert mcp.get_tool("missing") is None
+
+
+def test_get_tool_exposes_mutable_parameters_for_schema_updates() -> None:
+    """SDK-defined: callers can update a tool's inputSchema via get_tool after registration."""
+    mcp = MCPServer()
+
+    def act(action: str) -> str:  # pragma: no cover
+        return action
+
+    mcp.add_tool(act)
+    tool = mcp.get_tool("act")
+    assert tool is not None
+    tool.parameters = {
+        "type": "object",
+        "properties": {"action": {"type": "string", "const": "ping"}},
+        "required": ["action"],
+    }
+    assert mcp.get_tool("act") is tool
+    assert tool.parameters["properties"]["action"]["const"] == "ping"
+
+
 @pytest.mark.anyio
 async def test_middleware_kwarg_and_property_share_the_low_level_chain() -> None:
     """SDK-defined: `MCPServer(middleware=[...])` appends to the low-level chain after