support MCP logging, increase minimum mcp version to 1.6.0 (#1436)

Author: samuelcolvin

pydantic_ai_slim/pydantic_ai/mcp.py

@@ -9,7 +9,7 @@
 from typing import Any
 
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
-from mcp.types import JSONRPCMessage
+from mcp.types import JSONRPCMessage, LoggingLevel
 from typing_extensions import Self
 
 from pydantic_ai.tools import ToolDefinition
@@ -52,6 +52,11 @@ async def client_streams(
         raise NotImplementedError('MCP Server subclasses must implement this method.')
         yield
 
+    @abstractmethod
+    def _get_log_level(self) -> LoggingLevel | None:
+        """Get the log level for the MCP server."""
+        raise NotImplementedError('MCP Server subclasses must implement this method.')
+
     async def list_tools(self) -> list[ToolDefinition]:
         """Retrieve tools that are currently active on the server.
 
@@ -89,6 +94,8 @@ async def __aenter__(self) -> Self:
         self._client = await self._exit_stack.enter_async_context(client)
 
         await self._client.initialize()
+        if log_level := self._get_log_level():
+            await self._client.set_logging_level(log_level)
         self.is_running = True
         return self
 
@@ -150,6 +157,13 @@ async def main():
     By default the subprocess will not inherit any environment variables from the parent process.
     If you want to inherit the environment variables from the parent process, use `env=os.environ`.
     """
+    log_level: LoggingLevel | None = None
+    """The log level to set when connecting to the server, if any.
+
+    See <https://modelcontextprotocol.io/specification/2025-03-26/server/utilities/logging#logging> for more details.
+
+    If `None`, no log level will be set.
+    """
 
     cwd: str | Path | None = None
     """The working directory to use when spawning the process."""
@@ -164,6 +178,9 @@ async def client_streams(
         async with stdio_client(server=server) as (read_stream, write_stream):
             yield read_stream, write_stream
 
+    def _get_log_level(self) -> LoggingLevel | None:
+        return self.log_level
+
 
 @dataclass
 class MCPServerHTTP(MCPServer):
@@ -223,6 +240,13 @@ async def main():
     If no new messages are received within this time, the connection will be considered stale
     and may be closed. Defaults to 5 minutes (300 seconds).
     """
+    log_level: LoggingLevel | None = None
+    """The log level to set when connecting to the server, if any.
+
+    See <https://modelcontextprotocol.io/specification/2025-03-26/server/utilities/logging#logging> for more details.
+
+    If `None`, no log level will be set.
+    """
 
     @asynccontextmanager
     async def client_streams(
@@ -234,3 +258,6 @@ async def client_streams(
             url=self.url, headers=self.headers, timeout=self.timeout, sse_read_timeout=self.sse_read_timeout
         ) as (read_stream, write_stream):
             yield read_stream, write_stream
+
+    def _get_log_level(self) -> LoggingLevel | None:
+        return self.log_level

pydantic_ai_slim/pyproject.toml

@@ -69,7 +69,7 @@ tavily = ["tavily-python>=0.5.0"]
 # CLI
 cli = ["rich>=13", "prompt-toolkit>=3", "argcomplete>=3.5.0"]
 # MCP
-mcp = ["mcp>=1.5.0; python_version >= '3.10'"]
+mcp = ["mcp>=1.6.0; python_version >= '3.10'"]
 # Evals
 evals = ["pydantic-evals=={{ version }}"]
 

tests/mcp_server.py

@@ -1,6 +1,7 @@
-from mcp.server.fastmcp import FastMCP
+from mcp.server.fastmcp import Context, FastMCP
 
 mcp = FastMCP('PydanticAI MCP Server')
+log_level = 'unset'
 
 
 @mcp.tool()
@@ -16,4 +17,22 @@ async def celsius_to_fahrenheit(celsius: float) -> float:
     return (celsius * 9 / 5) + 32
 
 
-mcp.run()
+@mcp.tool()
+async def get_log_level(ctx: Context) -> str:  # type: ignore
+    """Get the current log level.
+
+    Returns:
+        The current log level.
+    """
+    await ctx.info('this is a log message')
+    return log_level
+
+
+@mcp._mcp_server.set_logging_level()  # pyright: ignore[reportPrivateUsage]
+async def set_logging_level(level: str) -> None:
+    global log_level
+    log_level = level
+
+
+if __name__ == '__main__':
+    mcp.run()

tests/test_mcp.py

@@ -31,7 +31,7 @@ async def test_stdio_server():
     server = MCPServerStdio('python', ['-m', 'tests.mcp_server'])
     async with server:
         tools = await server.list_tools()
-        assert len(tools) == 1
+        assert len(tools) == 2
         assert tools[0].name == 'celsius_to_fahrenheit'
         assert tools[0].description.startswith('Convert Celsius to Fahrenheit.')
 
@@ -45,12 +45,13 @@ async def test_stdio_server_with_cwd():
     server = MCPServerStdio('python', ['mcp_server.py'], cwd=test_dir)
     async with server:
         tools = await server.list_tools()
-        assert len(tools) == 1
+        assert len(tools) == 2
 
 
 def test_sse_server():
     sse_server = MCPServerHTTP(url='http://localhost:8000/sse')
     assert sse_server.url == 'http://localhost:8000/sse'
+    assert sse_server._get_log_level() is None  # pyright: ignore[reportPrivateUsage]
 
 
 def test_sse_server_with_header_and_timeout():
@@ -59,11 +60,13 @@ def test_sse_server_with_header_and_timeout():
         headers={'my-custom-header': 'my-header-value'},
         timeout=10,
         sse_read_timeout=100,
+        log_level='info',
     )
     assert sse_server.url == 'http://localhost:8000/sse'
     assert sse_server.headers is not None and sse_server.headers['my-custom-header'] == 'my-header-value'
     assert sse_server.timeout == 10
     assert sse_server.sse_read_timeout == 100
+    assert sse_server._get_log_level() == 'info'  # pyright: ignore[reportPrivateUsage]
 
 
 async def test_agent_with_stdio_server(allow_model_requests: None, openai_api_key: str):
@@ -114,3 +117,23 @@ async def test_agent_with_server_not_running(openai_api_key: str):
     agent = Agent(model, mcp_servers=[server])
     with pytest.raises(UserError, match='MCP server is not running'):
         await agent.run('What is 0 degrees Celsius in Fahrenheit?')
+
+
+async def test_log_level_unset():
+    server = MCPServerStdio('python', ['-m', 'tests.mcp_server'])
+    assert server._get_log_level() is None  # pyright: ignore[reportPrivateUsage]
+    async with server:
+        tools = await server.list_tools()
+        assert len(tools) == 2
+        assert tools[1].name == 'get_log_level'
+
+        result = await server.call_tool('get_log_level', {})
+        assert result.content == snapshot([TextContent(type='text', text='unset')])
+
+
+async def test_log_level_set():
+    server = MCPServerStdio('python', ['-m', 'tests.mcp_server'], log_level='info')
+    assert server._get_log_level() == 'info'  # pyright: ignore[reportPrivateUsage]
+    async with server:
+        result = await server.call_tool('get_log_level', {})
+        assert result.content == snapshot([TextContent(type='text', text='info')])