fix: align Context logging methods with MCP spec data type (#2366)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com>

Author: 3 people

README.v2.md

@@ -681,11 +681,11 @@ The Context object provides the following capabilities:
 - `ctx.mcp_server` - Access to the MCPServer server instance (see [MCPServer Properties](#mcpserver-properties))
 - `ctx.session` - Access to the underlying session for advanced communication (see [Session Properties and Methods](#session-properties-and-methods))
 - `ctx.request_context` - Access to request-specific data and lifespan resources (see [Request Context Properties](#request-context-properties))
-- `await ctx.debug(message)` - Send debug log message
-- `await ctx.info(message)` - Send info log message
-- `await ctx.warning(message)` - Send warning log message
-- `await ctx.error(message)` - Send error log message
-- `await ctx.log(level, message, logger_name=None)` - Send log with custom level
+- `await ctx.debug(data)` - Send debug log message
+- `await ctx.info(data)` - Send info log message
+- `await ctx.warning(data)` - Send warning log message
+- `await ctx.error(data)` - Send error log message
+- `await ctx.log(level, data, logger_name=None)` - Send log with custom level
 - `await ctx.report_progress(progress, total=None, message=None)` - Report operation progress
 - `await ctx.read_resource(uri)` - Read a resource by URI
 - `await ctx.elicit(message, schema)` - Request additional information from user with validation

docs/migration.md

@@ -467,6 +467,26 @@ mcp._lowlevel_server._add_request_handler("resources/subscribe", handle_subscrib
 
 This is a private API and may change. A public way to register these handlers on `MCPServer` is planned; until then, use this workaround or use the lowlevel `Server` directly.
 
+### `MCPServer`'s `Context` logging: `message` renamed to `data`, `extra` removed
+
+On the high-level `Context` object (`mcp.server.mcpserver.Context`), `log()`, `.debug()`, `.info()`, `.warning()`, and `.error()` now take `data: Any` instead of `message: str`, matching the MCP spec's `LoggingMessageNotificationParams.data` field which allows any JSON-serializable value. The `extra` parameter has been removed — pass structured data directly as `data`.
+
+The lowlevel `ServerSession.send_log_message(data: Any)` already accepted arbitrary data and is unchanged.
+
+`Context.log()` also now accepts all eight RFC-5424 log levels (`debug`, `info`, `notice`, `warning`, `error`, `critical`, `alert`, `emergency`) via the `LoggingLevel` type, not just the four it previously allowed.
+
+```python
+# Before
+await ctx.info("Connection failed", extra={"host": "localhost", "port": 5432})
+await ctx.log(level="info", message="hello")
+
+# After
+await ctx.info({"message": "Connection failed", "host": "localhost", "port": 5432})
+await ctx.log(level="info", data="hello")
+```
+
+Positional calls (`await ctx.info("hello")`) are unaffected.
+
 ### Replace `RootModel` by union types with `TypeAdapter` validation
 
 The following union types are no longer `RootModel` subclasses:

src/mcp/server/mcpserver/context.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from collections.abc import Iterable
-from typing import TYPE_CHECKING, Any, Generic, Literal
+from typing import TYPE_CHECKING, Any, Generic
 
 from pydantic import AnyUrl, BaseModel
 
@@ -14,6 +14,7 @@
     elicit_with_validation,
 )
 from mcp.server.lowlevel.helper_types import ReadResourceContents
+from mcp.types import LoggingLevel
 
 if TYPE_CHECKING:
     from mcp.server.mcpserver.server import MCPServer
@@ -186,29 +187,23 @@ async def elicit_url(
 
     async def log(
         self,
-        level: Literal["debug", "info", "warning", "error"],
-        message: str,
+        level: LoggingLevel,
+        data: Any,
         *,
         logger_name: str | None = None,
-        extra: dict[str, Any] | None = None,
     ) -> None:
         """Send a log message to the client.
 
         Args:
-            level: Log level (debug, info, warning, error)
-            message: Log message
+            level: Log level (debug, info, notice, warning, error, critical,
+                alert, emergency)
+            data: The data to be logged. Any JSON serializable type is allowed
+                (string, dict, list, number, bool, etc.) per the MCP specification.
             logger_name: Optional logger name
-            extra: Optional dictionary with additional structured data to include
         """
-
-        if extra:
-            log_data = {"message": message, **extra}
-        else:
-            log_data = message
-
         await self.request_context.session.send_log_message(
             level=level,
-            data=log_data,
+            data=data,
             logger=logger_name,
             related_request_id=self.request_id,
         )
@@ -261,20 +256,18 @@ async def close_standalone_sse_stream(self) -> None:
             await self._request_context.close_standalone_sse_stream()
 
     # Convenience methods for common log levels
-    async def debug(self, message: str, *, logger_name: str | None = None, extra: dict[str, Any] | None = None) -> None:
+    async def debug(self, data: Any, *, logger_name: str | None = None) -> None:
         """Send a debug log message."""
-        await self.log("debug", message, logger_name=logger_name, extra=extra)
+        await self.log("debug", data, logger_name=logger_name)
 
-    async def info(self, message: str, *, logger_name: str | None = None, extra: dict[str, Any] | None = None) -> None:
+    async def info(self, data: Any, *, logger_name: str | None = None) -> None:
         """Send an info log message."""
-        await self.log("info", message, logger_name=logger_name, extra=extra)
+        await self.log("info", data, logger_name=logger_name)
 
-    async def warning(
-        self, message: str, *, logger_name: str | None = None, extra: dict[str, Any] | None = None
-    ) -> None:
+    async def warning(self, data: Any, *, logger_name: str | None = None) -> None:
         """Send a warning log message."""
-        await self.log("warning", message, logger_name=logger_name, extra=extra)
+        await self.log("warning", data, logger_name=logger_name)
 
-    async def error(self, message: str, *, logger_name: str | None = None, extra: dict[str, Any] | None = None) -> None:
+    async def error(self, data: Any, *, logger_name: str | None = None) -> None:
         """Send an error log message."""
-        await self.log("error", message, logger_name=logger_name, extra=extra)
+        await self.log("error", data, logger_name=logger_name)

tests/client/test_logging_callback.py

@@ -1,4 +1,4 @@
-from typing import Any, Literal
+from typing import Literal
 
 import pytest
 
@@ -36,24 +36,20 @@ async def test_tool_with_log(
         message: str, level: Literal["debug", "info", "warning", "error"], logger: str, ctx: Context
     ) -> bool:
         """Send a log notification to the client."""
-        await ctx.log(level=level, message=message, logger_name=logger)
+        await ctx.log(level=level, data=message, logger_name=logger)
         return True
 
-    @server.tool("test_tool_with_log_extra")
-    async def test_tool_with_log_extra(
-        message: str,
+    @server.tool("test_tool_with_log_dict")
+    async def test_tool_with_log_dict(
         level: Literal["debug", "info", "warning", "error"],
         logger: str,
-        extra_string: str,
-        extra_dict: dict[str, Any],
         ctx: Context,
     ) -> bool:
-        """Send a log notification to the client with extra fields."""
+        """Send a log notification with a dict payload."""
         await ctx.log(
             level=level,
-            message=message,
+            data={"message": "Test log message", "extra_string": "example", "extra_dict": {"a": 1, "b": 2, "c": 3}},
             logger_name=logger,
-            extra={"extra_string": extra_string, "extra_dict": extra_dict},
         )
         return True
 
@@ -84,29 +80,26 @@ async def message_handler(
                 "logger": "test_logger",
             },
         )
-        log_result_with_extra = await client.call_tool(
-            "test_tool_with_log_extra",
+        log_result_with_dict = await client.call_tool(
+            "test_tool_with_log_dict",
             {
-                "message": "Test log message",
                 "level": "info",
                 "logger": "test_logger",
-                "extra_string": "example",
-                "extra_dict": {"a": 1, "b": 2, "c": 3},
             },
         )
         assert log_result.is_error is False
-        assert log_result_with_extra.is_error is False
+        assert log_result_with_dict.is_error is False
         assert len(logging_collector.log_messages) == 2
         # Create meta object with related_request_id added dynamically
         log = logging_collector.log_messages[0]
         assert log.level == "info"
         assert log.logger == "test_logger"
         assert log.data == "Test log message"
 
-        log_with_extra = logging_collector.log_messages[1]
-        assert log_with_extra.level == "info"
-        assert log_with_extra.logger == "test_logger"
-        assert log_with_extra.data == {
+        log_with_dict = logging_collector.log_messages[1]
+        assert log_with_dict.level == "info"
+        assert log_with_dict.logger == "test_logger"
+        assert log_with_dict.data == {
             "message": "Test log message",
             "extra_string": "example",
             "extra_dict": {"a": 1, "b": 2, "c": 3},