refactor: replace lowlevel Server decorators with on_* constructor kwargs (#1985)

examples/snippets/servers/lowlevel/structured_output.py

@@ -3,62 +3,67 @@ uv run examples/snippets/servers/lowlevel/structured_output.py
 """
 
 import asyncio
-from typing import Any
+import json
 
 import mcp.server.stdio
 from mcp import types
-from mcp.server.lowlevel import NotificationOptions, Server
-from mcp.server.models import InitializationOptions
-
-server = Server("example-server")
+from mcp.server import Server, ServerRequestContext
 
 
-@server.list_tools()
-async def list_tools() -> list[types.Tool]:
+async def handle_list_tools(
+    ctx: ServerRequestContext, params: types.PaginatedRequestParams | None
+) -> types.ListToolsResult:
     """List available tools with structured output schemas."""
-    return [
-        types.Tool(
-            name="get_weather",
-            description="Get current weather for a city",
-            input_schema={
-                "type": "object",
-                "properties": {"city": {"type": "string", "description": "City name"}},
-                "required": ["city"],
-            },
-            output_schema={
-                "type": "object",
-                "properties": {
-                    "temperature": {"type": "number", "description": "Temperature in Celsius"},
-                    "condition": {"type": "string", "description": "Weather condition"},
-                    "humidity": {"type": "number", "description": "Humidity percentage"},
-                    "city": {"type": "string", "description": "City name"},
+    return types.ListToolsResult(
+        tools=[
+            types.Tool(
+                name="get_weather",
+                description="Get current weather for a city",
+                input_schema={
+                    "type": "object",
+                    "properties": {"city": {"type": "string", "description": "City name"}},
+                    "required": ["city"],
                 },
-                "required": ["temperature", "condition", "humidity", "city"],
-            },
-        )
-    ]
+                output_schema={
+                    "type": "object",
+                    "properties": {
+                        "temperature": {"type": "number", "description": "Temperature in Celsius"},
+                        "condition": {"type": "string", "description": "Weather condition"},
+                        "humidity": {"type": "number", "description": "Humidity percentage"},
+                        "city": {"type": "string", "description": "City name"},
+                    },
+                    "required": ["temperature", "condition", "humidity", "city"],
+                },
+            )
+        ]
+    )
 
 
-@server.call_tool()
-async def call_tool(name: str, arguments: dict[str, Any]) -> dict[str, Any]:
+async def handle_call_tool(ctx: ServerRequestContext, params: types.CallToolRequestParams) -> types.CallToolResult:
     """Handle tool calls with structured output."""
-    if name == "get_weather":
-        city = arguments["city"]
+    if params.name == "get_weather":
+        city = (params.arguments or {})["city"]
 
-        # Simulated weather data - in production, call a weather API
         weather_data = {
             "temperature": 22.5,
             "condition": "partly cloudy",
             "humidity": 65,
-            "city": city,  # Include the requested city
+            "city": city,
         }
 
-        # low-level server will validate structured output against the tool's
-        # output schema, and additionally serialize it into a TextContent block
-        # for backwards compatibility with pre-2025-06-18 clients.
-        return weather_data
-    else:
-        raise ValueError(f"Unknown tool: {name}")
+        return types.CallToolResult(
+            content=[types.TextContent(type="text", text=json.dumps(weather_data, indent=2))],
+            structured_content=weather_data,
+        )
+
+    raise ValueError(f"Unknown tool: {params.name}")
+
+
+server = Server(
+    "example-server",
+    on_list_tools=handle_list_tools,
+    on_call_tool=handle_call_tool,
+)
 
 
 async def run():
@@ -67,14 +72,7 @@ async def run():
         await server.run(
             read_stream,
             write_stream,
-            InitializationOptions(
-                server_name="structured-output-example",
-                server_version="0.1.0",
-                capabilities=server.get_capabilities(
-                    notification_options=NotificationOptions(),
-                    experimental_capabilities={},
-                ),
-            ),
+            server.create_initialization_options(),
         )