README - replace code snippets with examples - add lowlevel to snippets (#1150)

examples/snippets/servers/lowlevel/__init__.py

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+"""Low-level server examples for MCP Python SDK."""

examples/snippets/servers/lowlevel/basic.py

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+"""
+Run from the repository root:
+uv run examples/snippets/servers/lowlevel/basic.py
+"""
+
+import asyncio
+
+import mcp.server.stdio
+import mcp.types as types
+from mcp.server.lowlevel import NotificationOptions, Server
+from mcp.server.models import InitializationOptions
+
+# Create a server instance
+server = Server("example-server")
+
+
+@server.list_prompts()
+async def handle_list_prompts() -> list[types.Prompt]:
+    """List available prompts."""
+    return [
+        types.Prompt(
+            name="example-prompt",
+            description="An example prompt template",
+            arguments=[types.PromptArgument(name="arg1", description="Example argument", required=True)],
+        )
+    ]
+
+
+@server.get_prompt()
+async def handle_get_prompt(name: str, arguments: dict[str, str] | None) -> types.GetPromptResult:
+    """Get a specific prompt by name."""
+    if name != "example-prompt":
+        raise ValueError(f"Unknown prompt: {name}")
+
+    arg1_value = (arguments or {}).get("arg1", "default")
+
+    return types.GetPromptResult(
+        description="Example prompt",
+        messages=[
+            types.PromptMessage(
+                role="user",
+                content=types.TextContent(type="text", text=f"Example prompt text with argument: {arg1_value}"),
+            )
+        ],
+    )
+
+
+async def run():
+    """Run the basic low-level server."""
+    async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
+        await server.run(
+            read_stream,
+            write_stream,
+            InitializationOptions(
+                server_name="example",
+                server_version="0.1.0",
+                capabilities=server.get_capabilities(
+                    notification_options=NotificationOptions(),
+                    experimental_capabilities={},
+                ),
+            ),
+        )
+
+
+if __name__ == "__main__":
+    asyncio.run(run())

examples/snippets/servers/lowlevel/lifespan.py

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+"""
+Run from the repository root:
+    uv run examples/snippets/servers/lowlevel/lifespan.py
+"""
+
+from collections.abc import AsyncIterator
+from contextlib import asynccontextmanager
+
+import mcp.server.stdio
+import mcp.types as types
+from mcp.server.lowlevel import NotificationOptions, Server
+from mcp.server.models import InitializationOptions
+
+
+# Mock database class for example
+class Database:
+    """Mock database class for example."""
+
+    @classmethod
+    async def connect(cls) -> "Database":
+        """Connect to database."""
+        print("Database connected")
+        return cls()
+
+    async def disconnect(self) -> None:
+        """Disconnect from database."""
+        print("Database disconnected")
+
+    async def query(self, query_str: str) -> list[dict[str, str]]:
+        """Execute a query."""
+        # Simulate database query
+        return [{"id": "1", "name": "Example", "query": query_str}]
+
+
+@asynccontextmanager
+async def server_lifespan(_server: Server) -> AsyncIterator[dict]:
+    """Manage server startup and shutdown lifecycle."""
+    # Initialize resources on startup
+    db = await Database.connect()
+    try:
+        yield {"db": db}
+    finally:
+        # Clean up on shutdown
+        await db.disconnect()
+
+
+# Pass lifespan to server
+server = Server("example-server", lifespan=server_lifespan)
+
+
+@server.list_tools()
+async def handle_list_tools() -> list[types.Tool]:
+    """List available tools."""
+    return [
+        types.Tool(
+            name="query_db",
+            description="Query the database",
+            inputSchema={
+                "type": "object",
+                "properties": {"query": {"type": "string", "description": "SQL query to execute"}},
+                "required": ["query"],
+            },
+        )
+    ]
+
+
+@server.call_tool()
+async def query_db(name: str, arguments: dict) -> list[types.TextContent]:
+    """Handle database query tool call."""
+    if name != "query_db":
+        raise ValueError(f"Unknown tool: {name}")
+
+    # Access lifespan context
+    ctx = server.request_context
+    db = ctx.lifespan_context["db"]
+
+    # Execute query
+    results = await db.query(arguments["query"])
+
+    return [types.TextContent(type="text", text=f"Query results: {results}")]
+
+
+async def run():
+    """Run the server with lifespan management."""
+    async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
+        await server.run(
+            read_stream,
+            write_stream,
+            InitializationOptions(
+                server_name="example-server",
+                server_version="0.1.0",
+                capabilities=server.get_capabilities(
+                    notification_options=NotificationOptions(),
+                    experimental_capabilities={},
+                ),
+            ),
+        )
+
+
+if __name__ == "__main__":
+    import asyncio
+
+    asyncio.run(run())

examples/snippets/servers/lowlevel/structured_output.py

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+"""
+Run from the repository root:
+    uv run examples/snippets/servers/lowlevel/structured_output.py
+"""
+
+import asyncio
+from typing import Any
+
+import mcp.server.stdio
+import mcp.types as types
+from mcp.server.lowlevel import NotificationOptions, Server
+from mcp.server.models import InitializationOptions
+
+server = Server("example-server")
+
+
+@server.list_tools()
+async def list_tools() -> list[types.Tool]:
+    """List available tools with structured output schemas."""
+    return [
+        types.Tool(
+            name="get_weather",
+            description="Get current weather for a city",
+            inputSchema={
+                "type": "object",
+                "properties": {"city": {"type": "string", "description": "City name"}},
+                "required": ["city"],
+            },
+            outputSchema={
+                "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]:
+    """Handle tool calls with structured output."""
+    if name == "get_weather":
+        city = arguments["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
+        }
+
+        # 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}")
+
+
+async def run():
+    """Run the structured output server."""
+    async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
+        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={},
+                ),
+            ),
+        )
+
+
+if __name__ == "__main__":
+    asyncio.run(run())