fix: change Resource URI fields from AnyUrl to str (#1863)

src/mcp/client/session.py

@@ -279,24 +279,24 @@ class ClientSession(
             types.ListResourceTemplatesResult,
         )
 
-    async def read_resource(self, uri: AnyUrl) -> types.ReadResourceResult:
+    async def read_resource(self, uri: str | AnyUrl) -> types.ReadResourceResult:
         """Send a resources/read request."""
         return await self.send_request(
-            types.ClientRequest(types.ReadResourceRequest(params=types.ReadResourceRequestParams(uri=uri))),
+            types.ClientRequest(types.ReadResourceRequest(params=types.ReadResourceRequestParams(uri=str(uri)))),
             types.ReadResourceResult,
         )
 
-    async def subscribe_resource(self, uri: AnyUrl) -> types.EmptyResult:
+    async def subscribe_resource(self, uri: str | AnyUrl) -> types.EmptyResult:
         """Send a resources/subscribe request."""
         return await self.send_request(  # pragma: no cover
-            types.ClientRequest(types.SubscribeRequest(params=types.SubscribeRequestParams(uri=uri))),
+            types.ClientRequest(types.SubscribeRequest(params=types.SubscribeRequestParams(uri=str(uri)))),
             types.EmptyResult,
         )
 
-    async def unsubscribe_resource(self, uri: AnyUrl) -> types.EmptyResult:
+    async def unsubscribe_resource(self, uri: str | AnyUrl) -> types.EmptyResult:
         """Send a resources/unsubscribe request."""
         return await self.send_request(  # pragma: no cover
-            types.ClientRequest(types.UnsubscribeRequest(params=types.UnsubscribeRequestParams(uri=uri))),
+            types.ClientRequest(types.UnsubscribeRequest(params=types.UnsubscribeRequestParams(uri=str(uri)))),
             types.EmptyResult,
         )
 

src/mcp/server/fastmcp/resources/base.py

@@ -1,14 +1,12 @@
 """Base classes and interfaces for FastMCP resources."""
 
 import abc
-from typing import Annotated, Any
+from typing import Any
 
 from pydantic import (
-    AnyUrl,
     BaseModel,
     ConfigDict,
     Field,
-    UrlConstraints,
     ValidationInfo,
     field_validator,
 )
@@ -21,7 +19,7 @@ class Resource(BaseModel, abc.ABC):
 
     model_config = ConfigDict(validate_default=True)
 
-    uri: Annotated[AnyUrl, UrlConstraints(host_required=False)] = Field(default=..., description="URI of the resource")
+    uri: str = Field(default=..., description="URI of the resource")
     name: str | None = Field(description="Name of the resource", default=None)
     title: str | None = Field(description="Human-readable title of the resource", default=None)
     description: str | None = Field(description="Description of the resource", default=None)

src/mcp/server/fastmcp/resources/types.py

@@ -11,7 +11,7 @@ import anyio.to_thread
 import httpx
 import pydantic
 import pydantic_core
-from pydantic import AnyUrl, Field, ValidationInfo, validate_call
+from pydantic import Field, ValidationInfo, validate_call
 
 from mcp.server.fastmcp.resources.base import Resource
 from mcp.types import Annotations, Icon
@@ -94,7 +94,7 @@ class FunctionResource(Resource):
         fn = validate_call(fn)
 
         return cls(
-            uri=AnyUrl(uri),
+            uri=uri,
             name=func_name,
             title=title,
             description=description or fn.__doc__ or "",

src/mcp/server/lowlevel/server.py

@@ -79,7 +79,6 @@ from typing import Any, Generic, TypeAlias, cast
 import anyio
 import jsonschema
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
-from pydantic import AnyUrl
 from typing_extensions import TypeVar
 
 import mcp.types as types
@@ -337,7 +336,7 @@ class Server(Generic[LifespanResultT, RequestT]):
 
     def read_resource(self):
         def decorator(
-            func: Callable[[AnyUrl], Awaitable[str | bytes | Iterable[ReadResourceContents]]],
+            func: Callable[[str], Awaitable[str | bytes | Iterable[ReadResourceContents]]],
         ):
             logger.debug("Registering handler for ReadResourceRequest")
 
@@ -412,7 +411,7 @@ class Server(Generic[LifespanResultT, RequestT]):
         return decorator
 
     def subscribe_resource(self):  # pragma: no cover
-        def decorator(func: Callable[[AnyUrl], Awaitable[None]]):
+        def decorator(func: Callable[[str], Awaitable[None]]):
             logger.debug("Registering handler for SubscribeRequest")
 
             async def handler(req: types.SubscribeRequest):
@@ -425,7 +424,7 @@ class Server(Generic[LifespanResultT, RequestT]):
         return decorator
 
     def unsubscribe_resource(self):  # pragma: no cover
-        def decorator(func: Callable[[AnyUrl], Awaitable[None]]):
+        def decorator(func: Callable[[str], Awaitable[None]]):
             logger.debug("Registering handler for UnsubscribeRequest")
 
             async def handler(req: types.UnsubscribeRequest):

src/mcp/server/session.py

@@ -227,12 +227,12 @@ class ServerSession(
             related_request_id,
         )
 
-    async def send_resource_updated(self, uri: AnyUrl) -> None:  # pragma: no cover
+    async def send_resource_updated(self, uri: str | AnyUrl) -> None:  # pragma: no cover
         """Send a resource updated notification."""
         await self.send_notification(
             types.ServerNotification(
                 types.ResourceUpdatedNotification(
-                    params=types.ResourceUpdatedNotificationParams(uri=uri),
+                    params=types.ResourceUpdatedNotificationParams(uri=str(uri)),
                 )
             )
         )

src/mcp/types.py

@@ -5,7 +5,6 @@ from datetime import datetime
 from typing import Annotated, Any, Final, Generic, Literal, TypeAlias, TypeVar
 
 from pydantic import BaseModel, ConfigDict, Field, FileUrl, RootModel
-from pydantic.networks import AnyUrl, UrlConstraints
 
 LATEST_PROTOCOL_VERSION = "2025-11-25"
 
@@ -756,7 +755,7 @@ class Annotations(BaseModel):
 class Resource(BaseMetadata):
     """A known resource that the server is capable of reading."""
 
-    uri: Annotated[AnyUrl, UrlConstraints(host_required=False)]
+    uri: str
     """The URI of this resource."""
     description: str | None = None
     """A description of what this resource represents."""
@@ -827,7 +826,7 @@ class ListResourceTemplatesResult(PaginatedResult):
 class ReadResourceRequestParams(RequestParams):
     """Parameters for reading a resource."""
 
-    uri: Annotated[AnyUrl, UrlConstraints(host_required=False)]
+    uri: str
     """
     The URI of the resource to read. The URI can use any protocol; it is up to the
     server how to interpret it.
@@ -845,7 +844,7 @@ class ReadResourceRequest(Request[ReadResourceRequestParams, Literal["resources/
 class ResourceContents(BaseModel):
     """The contents of a specific resource or sub-resource."""
 
-    uri: Annotated[AnyUrl, UrlConstraints(host_required=False)]
+    uri: str
     """The URI of this resource."""
     mimeType: str | None = None
     """The MIME type of this resource, if known."""
@@ -895,7 +894,7 @@ class ResourceListChangedNotification(
 class SubscribeRequestParams(RequestParams):
     """Parameters for subscribing to a resource."""
 
-    uri: Annotated[AnyUrl, UrlConstraints(host_required=False)]
+    uri: str
     """
     The URI of the resource to subscribe to. The URI can use any protocol; it is up to
     the server how to interpret it.
@@ -916,7 +915,7 @@ class SubscribeRequest(Request[SubscribeRequestParams, Literal["resources/subscr
 class UnsubscribeRequestParams(RequestParams):
     """Parameters for unsubscribing from a resource."""
 
-    uri: Annotated[AnyUrl, UrlConstraints(host_required=False)]
+    uri: str
     """The URI of the resource to unsubscribe from."""
     model_config = ConfigDict(extra="allow")
 
@@ -934,7 +933,7 @@ class UnsubscribeRequest(Request[UnsubscribeRequestParams, Literal["resources/un
 class ResourceUpdatedNotificationParams(NotificationParams):
     """Parameters for resource update notifications."""
 
-    uri: Annotated[AnyUrl, UrlConstraints(host_required=False)]
+    uri: str
     """
     The URI of the resource that has been updated. This might be a sub-resource of the
     one that the client actually subscribed to.