refactor: McpError renamed to MCPError and flatten parameters (#1956)

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

docs/experimental/tasks-client.md

@@ -337,7 +337,7 @@ if __name__ == "__main__":
 Handle task errors gracefully:
 
 ```python
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 
 try:
     result = await session.experimental.call_tool_as_task("my_tool", args)
@@ -349,8 +349,8 @@ try:
 
     final = await session.experimental.get_task_result(task_id, CallToolResult)
 
-except McpError as e:
+except MCPError as e:
-    print(f"MCP error: {e.error.message}")
+    print(f"MCP error: {e.message}")
 except Exception as e:
     print(f"Error: {e}")
 ```

docs/migration.md

@@ -121,6 +121,38 @@ result = await session.list_resources(params=PaginatedRequestParams(cursor="next
 result = await session.list_tools(params=PaginatedRequestParams(cursor="next_page_token"))
 ```
 
+### `McpError` renamed to `MCPError`
+
+The `McpError` exception class has been renamed to `MCPError` for consistent naming with the MCP acronym style used throughout the SDK.
+
+**Before (v1):**
+
+```python
+from mcp.shared.exceptions import McpError
+
+try:
+    result = await session.call_tool("my_tool")
+except McpError as e:
+    print(f"Error: {e.error.message}")
+```
+
+**After (v2):**
+
+```python
+from mcp.shared.exceptions import MCPError
+
+try:
+    result = await session.call_tool("my_tool")
+except MCPError as e:
+    print(f"Error: {e.message}")
+```
+
+`MCPError` is also exported from the top-level `mcp` package:
+
+```python
+from mcp import MCPError
+```
+
 ### `FastMCP` renamed to `MCPServer`
 
 The `FastMCP` class has been renamed to `MCPServer` to better reflect its role as the main server class in the SDK. This is a simple rename with no functional changes to the class itself.

examples/snippets/clients/url_elicitation_client.py

@@ -33,7 +33,7 @@ from urllib.parse import urlparse
 from mcp import ClientSession, types
 from mcp.client.sse import sse_client
 from mcp.shared.context import RequestContext
-from mcp.shared.exceptions import McpError, UrlElicitationRequiredError
+from mcp.shared.exceptions import MCPError, UrlElicitationRequiredError
 from mcp.types import URL_ELICITATION_REQUIRED
 
 
@@ -160,9 +160,9 @@ async def call_tool_with_error_handling(
 
         return result
 
-    except McpError as e:
+    except MCPError as e:
         # Check if this is a URL elicitation required error
-        if e.error.code == URL_ELICITATION_REQUIRED:
+        if e.code == URL_ELICITATION_REQUIRED:
             print("\n[Tool requires URL elicitation to proceed]")
 
             # Convert to typed error to access elicitations

src/mcp/__init__.py

@@ -4,7 +4,7 @@ from .client.session_group import ClientSessionGroup
 from .client.stdio import StdioServerParameters, stdio_client
 from .server.session import ServerSession
 from .server.stdio import stdio_server
-from .shared.exceptions import McpError, UrlElicitationRequiredError
+from .shared.exceptions import MCPError, UrlElicitationRequiredError
 from .types import (
     CallToolRequest,
     ClientCapabilities,
@@ -96,7 +96,7 @@ __all__ = [
     "ListToolsResult",
     "LoggingLevel",
     "LoggingMessageNotification",
-    "McpError",
+    "MCPError",
     "Notification",
     "PingRequest",
     "ProgressNotification",

src/mcp/client/session_group.py

@@ -25,7 +25,7 @@ from mcp.client.sse import sse_client
 from mcp.client.stdio import StdioServerParameters
 from mcp.client.streamable_http import streamable_http_client
 from mcp.shared._httpx_utils import create_mcp_http_client
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 from mcp.shared.session import ProgressFnT
 
 
@@ -216,11 +216,9 @@ class ClientSessionGroup:
         session_known_for_stack = session in self._session_exit_stacks
 
         if not session_known_for_components and not session_known_for_stack:
-            raise McpError(
+            raise MCPError(
-                types.ErrorData(
+                code=types.INVALID_PARAMS,
-                    code=types.INVALID_PARAMS,
+                message="Provided session is not managed or already disconnected.",
-                    message="Provided session is not managed or already disconnected.",
-                )
             )
 
         if session_known_for_components:  # pragma: no branch
@@ -352,7 +350,7 @@ class ClientSessionGroup:
                 name = self._component_name(prompt.name, server_info)
                 prompts_temp[name] = prompt
                 component_names.prompts.add(name)
-        except McpError as err:  # pragma: no cover
+        except MCPError as err:  # pragma: no cover
             logging.warning(f"Could not fetch prompts: {err}")
 
         # Query the server for its resources and aggregate to list.
@@ -362,7 +360,7 @@ class ClientSessionGroup:
                 name = self._component_name(resource.name, server_info)
                 resources_temp[name] = resource
                 component_names.resources.add(name)
-        except McpError as err:  # pragma: no cover
+        except MCPError as err:  # pragma: no cover
             logging.warning(f"Could not fetch resources: {err}")
 
         # Query the server for its tools and aggregate to list.
@@ -373,7 +371,7 @@ class ClientSessionGroup:
                 tools_temp[name] = tool
                 tool_to_session_temp[name] = session
                 component_names.tools.add(name)
-        except McpError as err:  # pragma: no cover
+        except MCPError as err:  # pragma: no cover
             logging.warning(f"Could not fetch tools: {err}")
 
         # Clean up exit stack for session if we couldn't retrieve anything
@@ -384,28 +382,19 @@ class ClientSessionGroup:
         # Check for duplicates.
         matching_prompts = prompts_temp.keys() & self._prompts.keys()
         if matching_prompts:
-            raise McpError(  # pragma: no cover
+            raise MCPError(  # pragma: no cover
-                types.ErrorData(
+                code=types.INVALID_PARAMS,
-                    code=types.INVALID_PARAMS,
+                message=f"{matching_prompts} already exist in group prompts.",
-                    message=f"{matching_prompts} already exist in group prompts.",
-                )
             )
         matching_resources = resources_temp.keys() & self._resources.keys()
         if matching_resources:
-            raise McpError(  # pragma: no cover
+            raise MCPError(  # pragma: no cover
-                types.ErrorData(
+                code=types.INVALID_PARAMS,
-                    code=types.INVALID_PARAMS,
+                message=f"{matching_resources} already exist in group resources.",
-                    message=f"{matching_resources} already exist in group resources.",
-                )
             )
         matching_tools = tools_temp.keys() & self._tools.keys()
         if matching_tools:
-            raise McpError(
+            raise MCPError(code=types.INVALID_PARAMS, message=f"{matching_tools} already exist in group tools.")
-                types.ErrorData(
-                    code=types.INVALID_PARAMS,
-                    message=f"{matching_tools} already exist in group tools.",
-                )
-            )
 
         # Aggregate components.
         self._sessions[session] = component_names

src/mcp/server/experimental/request_context.py

@@ -13,7 +13,7 @@ from typing import Any
 from mcp.server.experimental.task_context import ServerTaskContext
 from mcp.server.experimental.task_support import TaskSupport
 from mcp.server.session import ServerSession
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 from mcp.shared.experimental.tasks.helpers import MODEL_IMMEDIATE_RESPONSE_KEY, is_terminal
 from mcp.types import (
     METHOD_NOT_FOUND,
@@ -72,13 +72,13 @@ class Experimental:
         Args:
             tool_task_mode: The tool's execution.taskSupport value
                 ("forbidden", "optional", "required", or None)
-            raise_error: If True, raises McpError on validation failure. If False, returns ErrorData.
+            raise_error: If True, raises MCPError on validation failure. If False, returns ErrorData.
 
         Returns:
             None if valid, ErrorData if invalid and raise_error=False
 
         Raises:
-            McpError: If invalid and raise_error=True
+            MCPError: If invalid and raise_error=True
         """
 
         mode = tool_task_mode or TASK_FORBIDDEN
@@ -86,18 +86,12 @@ class Experimental:
         error: ErrorData | None = None
 
         if mode == TASK_REQUIRED and not self.is_task:
-            error = ErrorData(
+            error = ErrorData(code=METHOD_NOT_FOUND, message="This tool requires task-augmented invocation")
-                code=METHOD_NOT_FOUND,
-                message="This tool requires task-augmented invocation",
-            )
         elif mode == TASK_FORBIDDEN and self.is_task:
-            error = ErrorData(
+            error = ErrorData(code=METHOD_NOT_FOUND, message="This tool does not support task-augmented invocation")
-                code=METHOD_NOT_FOUND,
-                message="This tool does not support task-augmented invocation",
-            )
 
         if error is not None and raise_error:
-            raise McpError(error)
+            raise MCPError(code=error.code, message=error.message)
 
         return error
 
@@ -113,7 +107,7 @@ class Experimental:
 
         Args:
             tool: The Tool definition
-            raise_error: If True, raises McpError on validation failure.
+            raise_error: If True, raises MCPError on validation failure.
 
         Returns:
             None if valid, ErrorData if invalid and raise_error=False

src/mcp/server/experimental/session_features.py

@@ -114,7 +114,7 @@ class ExperimentalServerSessionFeatures:
             The client's elicitation response
 
         Raises:
-            McpError: If client doesn't support task-augmented elicitation
+            MCPError: If client doesn't support task-augmented elicitation
         """
         client_caps = self._session.client_params.capabilities if self._session.client_params else None
         require_task_augmented_elicitation(client_caps)
@@ -174,7 +174,7 @@ class ExperimentalServerSessionFeatures:
             The sampling result from the client
 
         Raises:
-            McpError: If client doesn't support task-augmented sampling or tools
+            MCPError: If client doesn't support task-augmented sampling or tools
             ValueError: If tool_use or tool_result message structure is invalid
         """
         client_caps = self._session.client_params.capabilities if self._session.client_params else None

src/mcp/server/experimental/task_context.py

@@ -13,7 +13,7 @@ import anyio
 from mcp.server.experimental.task_result_handler import TaskResultHandler
 from mcp.server.session import ServerSession
 from mcp.server.validation import validate_sampling_tools, validate_tool_use_result_messages
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 from mcp.shared.experimental.tasks.capabilities import (
     require_task_augmented_elicitation,
     require_task_augmented_sampling,
@@ -32,7 +32,6 @@ from mcp.types import (
     ElicitationCapability,
     ElicitRequestedSchema,
     ElicitResult,
-    ErrorData,
     IncludeContext,
     ModelPreferences,
     RequestId,
@@ -173,22 +172,12 @@ class ServerTaskContext:
     def _check_elicitation_capability(self) -> None:
         """Check if the client supports elicitation."""
         if not self._session.check_client_capability(ClientCapabilities(elicitation=ElicitationCapability())):
-            raise McpError(
+            raise MCPError(code=INVALID_REQUEST, message="Client does not support elicitation capability")
-                ErrorData(
-                    code=INVALID_REQUEST,
-                    message="Client does not support elicitation capability",
-                )
-            )
 
     def _check_sampling_capability(self) -> None:
         """Check if the client supports sampling."""
         if not self._session.check_client_capability(ClientCapabilities(sampling=SamplingCapability())):
-            raise McpError(
+            raise MCPError(code=INVALID_REQUEST, message="Client does not support sampling capability")
-                ErrorData(
-                    code=INVALID_REQUEST,
-                    message="Client does not support sampling capability",
-                )
-            )
 
     async def elicit(
         self,
@@ -213,7 +202,7 @@ class ServerTaskContext:
             The client's response
 
         Raises:
-            McpError: If client doesn't support elicitation capability
+            MCPError: If client doesn't support elicitation capability
         """
         self._check_elicitation_capability()
 
@@ -281,7 +270,7 @@ class ServerTaskContext:
             The client's response indicating acceptance, decline, or cancellation
 
         Raises:
-            McpError: If client doesn't support elicitation capability
+            MCPError: If client doesn't support elicitation capability
             RuntimeError: If handler is not configured
         """
         self._check_elicitation_capability()
@@ -361,7 +350,7 @@ class ServerTaskContext:
             The sampling result from the client
 
         Raises:
-            McpError: If client doesn't support sampling capability or tools
+            MCPError: If client doesn't support sampling capability or tools
             ValueError: If tool_use or tool_result message structure is invalid
         """
         self._check_sampling_capability()
@@ -436,7 +425,7 @@ class ServerTaskContext:
             The client's elicitation response
 
         Raises:
-            McpError: If client doesn't support task-augmented elicitation
+            MCPError: If client doesn't support task-augmented elicitation
             RuntimeError: If handler is not configured
         """
         client_caps = self._session.client_params.capabilities if self._session.client_params else None
@@ -529,7 +518,7 @@ class ServerTaskContext:
             The sampling result from the client
 
         Raises:
-            McpError: If client doesn't support task-augmented sampling or tools
+            MCPError: If client doesn't support task-augmented sampling or tools
             ValueError: If tool_use or tool_result message structure is invalid
             RuntimeError: If handler is not configured
         """

src/mcp/server/experimental/task_result_handler.py

@@ -15,7 +15,7 @@ from typing import Any
 import anyio
 
 from mcp.server.session import ServerSession
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 from mcp.shared.experimental.tasks.helpers import RELATED_TASK_METADATA_KEY, is_terminal
 from mcp.shared.experimental.tasks.message_queue import TaskMessageQueue
 from mcp.shared.experimental.tasks.resolver import Resolver
@@ -106,7 +106,7 @@ class TaskResultHandler:
         while True:
             task = await self._store.get_task(task_id)
             if task is None:
-                raise McpError(ErrorData(code=INVALID_PARAMS, message=f"Task not found: {task_id}"))
+                raise MCPError(code=INVALID_PARAMS, message=f"Task not found: {task_id}")
 
             await self._deliver_queued_messages(task_id, session, request_id)
 
@@ -216,6 +216,6 @@ class TaskResultHandler:
         """
         resolver = self._pending_requests.pop(request_id, None)
         if resolver is not None and not resolver.done():
-            resolver.set_exception(McpError(error))
+            resolver.set_exception(MCPError.from_error_data(error))
             return True
         return False

src/mcp/server/lowlevel/experimental.py

@@ -11,7 +11,7 @@ from typing import TYPE_CHECKING
 
 from mcp.server.experimental.task_support import TaskSupport
 from mcp.server.lowlevel.func_inspection import create_call_wrapper
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 from mcp.shared.experimental.tasks.helpers import cancel_task
 from mcp.shared.experimental.tasks.in_memory_task_store import InMemoryTaskStore
 from mcp.shared.experimental.tasks.message_queue import InMemoryTaskMessageQueue, TaskMessageQueue
@@ -20,7 +20,6 @@ from mcp.types import (
     INVALID_PARAMS,
     CancelTaskRequest,
     CancelTaskResult,
-    ErrorData,
     GetTaskPayloadRequest,
     GetTaskPayloadResult,
     GetTaskRequest,
@@ -135,12 +134,7 @@ class ExperimentalHandlers:
             async def _default_get_task(req: GetTaskRequest) -> ServerResult:
                 task = await support.store.get_task(req.params.task_id)
                 if task is None:
-                    raise McpError(
+                    raise MCPError(code=INVALID_PARAMS, message=f"Task not found: {req.params.task_id}")
-                        ErrorData(
-                            code=INVALID_PARAMS,
-                            message=f"Task not found: {req.params.task_id}",
-                        )
-                    )
                 return GetTaskResult(
                     task_id=task.task_id,
                     status=task.status,

src/mcp/server/lowlevel/server.py

@@ -101,7 +101,7 @@ from mcp.server.streamable_http import EventStore
 from mcp.server.streamable_http_manager import StreamableHTTPASGIApp, StreamableHTTPSessionManager
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.shared.context import RequestContext
-from mcp.shared.exceptions import McpError, UrlElicitationRequiredError
+from mcp.shared.exceptions import MCPError, UrlElicitationRequiredError
 from mcp.shared.message import ServerMessageMetadata, SessionMessage
 from mcp.shared.session import RequestResponder
 from mcp.shared.tool_name_validation import validate_and_warn_tool_name
@@ -407,9 +407,7 @@ class Server(Generic[LifespanResultT, RequestT]):
                     case _:  # pragma: no cover
                         raise ValueError(f"Unexpected return type from read_resource: {type(result)}")
 
-                return types.ReadResourceResult(  # pragma: no cover
+                return types.ReadResourceResult(contents=[content])  # pragma: no cover
-                    contents=[content],
-                )
 
             self.request_handlers[types.ReadResourceRequest] = handler
             return func
@@ -781,13 +779,10 @@ class Server(Generic[LifespanResultT, RequestT]):
                     )
                 )
                 response = await handler(req)
-            except McpError as err:
+            except MCPError as err:
                 response = err.error
             except anyio.get_cancelled_exc_class():
-                logger.info(
+                logger.info("Request %s cancelled - duplicate response suppressed", message.request_id)
-                    "Request %s cancelled - duplicate response suppressed",
-                    message.request_id,
-                )
                 return
             except Exception as err:
                 if raise_exceptions:  # pragma: no cover

src/mcp/server/session.py

@@ -314,7 +314,7 @@ class ServerSession(
             The sampling result from the client.
 
         Raises:
-            McpError: If tools are provided but client doesn't support them.
+            MCPError: If tools are provided but client doesn't support them.
             ValueError: If tool_use or tool_result message structure is invalid.
             StatelessModeNotSupported: If called in stateless HTTP mode.
         """

src/mcp/server/validation.py

@@ -4,15 +4,8 @@ This module provides validation logic for sampling and elicitation requests
 that is shared across normal and task-augmented code paths.
 """
 
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
-from mcp.types import (
+from mcp.types import INVALID_PARAMS, ClientCapabilities, SamplingMessage, Tool, ToolChoice
-    INVALID_PARAMS,
-    ClientCapabilities,
-    ErrorData,
-    SamplingMessage,
-    Tool,
-    ToolChoice,
-)
 
 
 def check_sampling_tools_capability(client_caps: ClientCapabilities | None) -> bool:
@@ -46,11 +39,11 @@ def validate_sampling_tools(
         tool_choice: The tool choice setting, if provided
 
     Raises:
-        McpError: If tools/tool_choice are provided but client doesn't support them
+        MCPError: If tools/tool_choice are provided but client doesn't support them
     """
     if tools is not None or tool_choice is not None:
         if not check_sampling_tools_capability(client_caps):
-            raise McpError(ErrorData(code=INVALID_PARAMS, message="Client does not support sampling tools capability"))
+            raise MCPError(code=INVALID_PARAMS, message="Client does not support sampling tools capability")
 
 
 def validate_tool_use_result_messages(messages: list[SamplingMessage]) -> None:

src/mcp/shared/exceptions.py

@@ -2,18 +2,40 @@ from __future__ import annotations
 
 from typing import Any, cast
 
-from mcp.types import URL_ELICITATION_REQUIRED, ElicitRequestURLParams, ErrorData
+from mcp.types import URL_ELICITATION_REQUIRED, ElicitRequestURLParams, ErrorData, JSONRPCError
 
 
-class McpError(Exception):
+class MCPError(Exception):
     """Exception type raised when an error arrives over an MCP connection."""
 
     error: ErrorData
 
-    def __init__(self, error: ErrorData):
+    def __init__(self, code: int, message: str, data: Any = None):
-        """Initialize McpError."""
+        super().__init__(code, message, data)
-        super().__init__(error.message)
+        self.error = ErrorData(code=code, message=message, data=data)
-        self.error = error
+
+    @property
+    def code(self) -> int:
+        return self.error.code
+
+    @property
+    def message(self) -> str:
+        return self.error.message
+
+    @property
+    def data(self) -> Any:
+        return self.error.data  # pragma: no cover
+
+    @classmethod
+    def from_jsonrpc_error(cls, error: JSONRPCError) -> MCPError:
+        return cls.from_error_data(error.error)
+
+    @classmethod
+    def from_error_data(cls, error: ErrorData) -> MCPError:
+        return cls(code=error.code, message=error.message, data=error.data)
+
+    def __str__(self) -> str:
+        return self.message
 
 
 class StatelessModeNotSupported(RuntimeError):
@@ -33,7 +55,7 @@ class StatelessModeNotSupported(RuntimeError):
         self.method = method
 
 
-class UrlElicitationRequiredError(McpError):
+class UrlElicitationRequiredError(MCPError):
     """Specialized error for when a tool requires URL mode elicitation(s) before proceeding.
 
     Servers can raise this error from tool handlers to indicate that the client
@@ -42,7 +64,6 @@ class UrlElicitationRequiredError(McpError):
     Example:
         raise UrlElicitationRequiredError([
             ElicitRequestURLParams(
-                mode="url",
                 message="Authorization required for your files",
                 url="https://example.com/oauth/authorize",
                 elicitation_id="auth-001"
@@ -50,23 +71,18 @@ class UrlElicitationRequiredError(McpError):
         ])
     """
 
-    def __init__(
+    def __init__(self, elicitations: list[ElicitRequestURLParams], message: str | None = None):
-        self,
-        elicitations: list[ElicitRequestURLParams],
-        message: str | None = None,
-    ):
         """Initialize UrlElicitationRequiredError."""
         if message is None:
             message = f"URL elicitation{'s' if len(elicitations) > 1 else ''} required"
 
         self._elicitations = elicitations
 
-        error = ErrorData(
+        super().__init__(
             code=URL_ELICITATION_REQUIRED,
             message=message,
             data={"elicitations": [e.model_dump(by_alias=True, exclude_none=True) for e in elicitations]},
         )
-        super().__init__(error)
 
     @property
     def elicitations(self) -> list[ElicitRequestURLParams]:

src/mcp/shared/experimental/tasks/capabilities.py

@@ -7,13 +7,8 @@ the main session code clean.
 WARNING: These APIs are experimental and may change without notice.
 """
 
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
-from mcp.types import (
+from mcp.types import INVALID_REQUEST, ClientCapabilities, ClientTasksCapability
-    INVALID_REQUEST,
-    ClientCapabilities,
-    ClientTasksCapability,
-    ErrorData,
-)
 
 
 def check_tasks_capability(
@@ -76,36 +71,26 @@ def has_task_augmented_sampling(caps: ClientCapabilities) -> bool:
 
 
 def require_task_augmented_elicitation(client_caps: ClientCapabilities | None) -> None:
-    """Raise McpError if client doesn't support task-augmented elicitation.
+    """Raise MCPError if client doesn't support task-augmented elicitation.
 
     Args:
         client_caps: The client's declared capabilities, or None if not initialized
 
     Raises:
-        McpError: If client doesn't support task-augmented elicitation
+        MCPError: If client doesn't support task-augmented elicitation
     """
     if client_caps is None or not has_task_augmented_elicitation(client_caps):
-        raise McpError(
+        raise MCPError(code=INVALID_REQUEST, message="Client does not support task-augmented elicitation")
-            ErrorData(
-                code=INVALID_REQUEST,
-                message="Client does not support task-augmented elicitation",
-            )
-        )
 
 
 def require_task_augmented_sampling(client_caps: ClientCapabilities | None) -> None:
-    """Raise McpError if client doesn't support task-augmented sampling.
+    """Raise MCPError if client doesn't support task-augmented sampling.
 
     Args:
         client_caps: The client's declared capabilities, or None if not initialized
 
     Raises:
-        McpError: If client doesn't support task-augmented sampling
+        MCPError: If client doesn't support task-augmented sampling
     """
     if client_caps is None or not has_task_augmented_sampling(client_caps):
-        raise McpError(
+        raise MCPError(code=INVALID_REQUEST, message="Client does not support task-augmented sampling")
-            ErrorData(
-                code=INVALID_REQUEST,
-                message="Client does not support task-augmented sampling",
-            )
-        )

src/mcp/shared/experimental/tasks/helpers.py

@@ -9,7 +9,7 @@ from contextlib import asynccontextmanager
 from datetime import datetime, timezone
 from uuid import uuid4
 
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 from mcp.shared.experimental.tasks.context import TaskContext
 from mcp.shared.experimental.tasks.store import TaskStore
 from mcp.types import (
@@ -19,7 +19,6 @@ from mcp.types import (
     TASK_STATUS_FAILED,
     TASK_STATUS_WORKING,
     CancelTaskResult,
-    ErrorData,
     Task,
     TaskMetadata,
     TaskStatus,
@@ -68,7 +67,7 @@ async def cancel_task(
         CancelTaskResult with the cancelled task state
 
     Raises:
-        McpError: With INVALID_PARAMS (-32602) if:
+        MCPError: With INVALID_PARAMS (-32602) if:
             - Task does not exist
             - Task is already in a terminal state (completed, failed, cancelled)
 
@@ -79,20 +78,10 @@ async def cancel_task(
     """
     task = await store.get_task(task_id)
     if task is None:
-        raise McpError(
+        raise MCPError(code=INVALID_PARAMS, message=f"Task not found: {task_id}")
-            ErrorData(
-                code=INVALID_PARAMS,
-                message=f"Task not found: {task_id}",
-            )
-        )
 
     if is_terminal(task.status):
-        raise McpError(
+        raise MCPError(code=INVALID_PARAMS, message=f"Cannot cancel task in terminal state '{task.status}'")
-            ErrorData(
-                code=INVALID_PARAMS,
-                message=f"Cannot cancel task in terminal state '{task.status}'",
-            )
-        )
 
     # Update task to cancelled status
     cancelled_task = await store.update_task(task_id, status=TASK_STATUS_CANCELLED)

src/mcp/shared/session.py

@@ -11,7 +11,7 @@ from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStre
 from pydantic import BaseModel, TypeAdapter
 from typing_extensions import Self
 
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 from mcp.shared.message import MessageMetadata, ServerMessageMetadata, SessionMessage
 from mcp.shared.response_router import ResponseRouter
 from mcp.types import (
@@ -237,7 +237,7 @@ class BaseSession(
     ) -> ReceiveResultT:
         """Sends a request and wait for a response.
 
-        Raises an McpError if the response contains an error. If a request read timeout is provided, it will take
+        Raises an MCPError if the response contains an error. If a request read timeout is provided, it will take
         precedence over the session read timeout.
 
         Do not use this method to emit notifications! Use send_notification() instead.
@@ -271,18 +271,12 @@ class BaseSession(
                 with anyio.fail_after(timeout):
                     response_or_error = await response_stream_reader.receive()
             except TimeoutError:
-                raise McpError(
+                class_name = request.__class__.__name__
-                    ErrorData(
+                message = f"Timed out while waiting for response to {class_name}. Waited {timeout} seconds."
-                        code=REQUEST_TIMEOUT,
+                raise MCPError(code=REQUEST_TIMEOUT, message=message)
-                        message=(
-                            f"Timed out while waiting for response to {request.__class__.__name__}. "
-                            f"Waited {timeout} seconds."
-                        ),
-                    )
-                )
 
             if isinstance(response_or_error, JSONRPCError):
-                raise McpError(response_or_error.error)
+                raise MCPError.from_jsonrpc_error(response_or_error)
             else:
                 return result_type.model_validate(response_or_error.result, by_name=False)
 

src/mcp/types/_types.py

@@ -1654,8 +1654,8 @@ class ElicitRequestURLParams(RequestParams):
     """The URL that the user should navigate to."""
 
     elicitation_id: str
-    """
+    """The ID of the elicitation, which must be unique within the context of the server.
-    The ID of the elicitation, which must be unique within the context of the server.
+
     The client MUST treat this ID as an opaque value.
     """
 

src/mcp/types/jsonrpc.py

@@ -59,15 +59,15 @@ class ErrorData(BaseModel):
     """The error type that occurred."""
 
     message: str
-    """
+    """A short description of the error.
-    A short description of the error. The message SHOULD be limited to a concise single
+
-    sentence.
+    The message SHOULD be limited to a concise single sentence.
     """
 
     data: Any = None
-    """
+    """Additional information about the error.
-    Additional information about the error. The value of this member is defined by the
+
-    sender (e.g. detailed error information, nested errors etc.).
+    The value of this member is defined by the sender (e.g. detailed error information, nested errors, etc.).
     """
 
 

tests/client/test_session_group.py

@@ -13,7 +13,7 @@ from mcp.client.session_group import (
     StreamableHttpParameters,
 )
 from mcp.client.stdio import StdioServerParameters
-from mcp.shared.exceptions import McpError
+from mcp.shared.exceptions import MCPError
 
 
 @pytest.fixture
@@ -225,7 +225,7 @@ async def test_client_session_group_disconnect_from_server():
 async def test_client_session_group_connect_to_server_duplicate_tool_raises_error(
     mock_exit_stack: contextlib.AsyncExitStack,
 ):
-    """Test McpError raised when connecting a server with a dup name."""
+    """Test MCPError raised when connecting a server with a dup name."""
     # --- Setup Pre-existing State ---
     group = ClientSessionGroup(exit_stack=mock_exit_stack)
     existing_tool_name = "shared_tool"
@@ -251,7 +251,7 @@ async def test_client_session_group_connect_to_server_duplicate_tool_raises_erro
     mock_session_new.list_prompts.return_value = mock.AsyncMock(prompts=[])
 
     # --- Test Execution and Assertion ---
-    with pytest.raises(McpError) as excinfo:
+    with pytest.raises(MCPError) as excinfo:
         with mock.patch.object(
             group,
             "_establish_session",
@@ -274,7 +274,7 @@ async def test_client_session_group_disconnect_non_existent_server():
     """Test disconnecting a server that isn't connected."""
     session = mock.Mock(spec=mcp.ClientSession)
     group = ClientSessionGroup()
-    with pytest.raises(McpError):
+    with pytest.raises(MCPError):
         await group.disconnect_from_server(session)