From 78f270cdeff52c11c58dc640dee8fa0c727c266e Mon Sep 17 00:00:00 2001
From: Vincent <0426vincent@gmail.com>
Date: Sat, 1 Nov 2025 22:41:07 -0700
Subject: [PATCH 1/3] fix: Support string enum for elicitation

---
 src/mcp/server/elicitation.py            |  7 ++++-
 tests/server/fastmcp/test_elicitation.py | 34 ++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/src/mcp/server/elicitation.py b/src/mcp/server/elicitation.py
index 49195415b..ab2c9ad6a 100644
--- a/src/mcp/server/elicitation.py
+++ b/src/mcp/server/elicitation.py
@@ -4,6 +4,7 @@
 
 import types
 from collections.abc import Sequence
+from enum import Enum, StrEnum
 from typing import Generic, Literal, TypeVar, Union, get_args, get_origin
 
 from pydantic import BaseModel
@@ -46,7 +47,7 @@ class AcceptedUrlElicitation(BaseModel):
 
 
 # Primitive types allowed in elicitation schemas
-_ELICITATION_PRIMITIVE_TYPES = (str, int, float, bool)
+_ELICITATION_PRIMITIVE_TYPES = (str, int, float, bool, StrEnum)
 
 
 def _validate_elicitation_schema(schema: type[BaseModel]) -> None:
@@ -99,6 +100,10 @@ def _is_primitive_field(annotation: type) -> bool:
             arg is types.NoneType or arg in _ELICITATION_PRIMITIVE_TYPES or _is_string_sequence(arg) for arg in args
         )
 
+    # Handle Enum types
+    if issubclass(annotation, str) and issubclass(annotation, Enum):
+        return True
+
     return False
 
 
diff --git a/tests/server/fastmcp/test_elicitation.py b/tests/server/fastmcp/test_elicitation.py
index 597b29178..6ca0a63ba 100644
--- a/tests/server/fastmcp/test_elicitation.py
+++ b/tests/server/fastmcp/test_elicitation.py
@@ -2,6 +2,7 @@
 Test the elicitation feature using stdio transport.
 """
 
+from enum import StrEnum
 from typing import Any
 
 import pytest
@@ -147,6 +148,39 @@ async def elicitation_callback(
             assert "Validation failed as expected" in result.content[0].text
             assert field_name in result.content[0].text
 
+    # Test valid Enum types (should not fail validation)
+    class Status(StrEnum):
+        ACTIVE = "active"
+        INACTIVE = "inactive"
+
+    class ValidStrEnumSchema(BaseModel):
+        status: Status = Field(description="Status using StrEnum")
+
+    def create_valid_validation_tool(name: str, schema_class: type[BaseModel]):
+        @mcp.tool(name=name, description=f"Tool testing {name}")
+        async def tool(ctx: Context[ServerSession, None]) -> str:
+            # This should succeed without validation error
+            result = await ctx.elicit(message="Test valid schema", schema=schema_class)
+            return f"Success: {result.action}"
+
+        return tool
+
+    create_valid_validation_tool("valid_strenum", ValidStrEnumSchema)
+
+    async def enum_callback(context: RequestContext[ClientSession, None], params: ElicitRequestParams):
+        # Return the required status field
+        return ElicitResult(action="accept", content={"status": "active"})
+
+    async with create_connected_server_and_client_session(
+        mcp._mcp_server, elicitation_callback=enum_callback
+    ) as client_session:
+        await client_session.initialize()
+
+        result = await client_session.call_tool("valid_strenum", {})
+        assert len(result.content) == 1
+        assert isinstance(result.content[0], TextContent)
+        assert "Success: accept" == result.content[0].text
+
 
 @pytest.mark.anyio
 async def test_elicitation_with_optional_fields():

From 97b156ddabccc9c8a03a51a494ed764f813c3d43 Mon Sep 17 00:00:00 2001
From: Vincent <0426vincent@gmail.com>
Date: Sat, 1 Nov 2025 23:03:23 -0700
Subject: [PATCH 2/3] fix: Remove StrEnum due to versioning

---
 src/mcp/server/elicitation.py            | 4 ++--
 tests/server/fastmcp/test_elicitation.py | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/mcp/server/elicitation.py b/src/mcp/server/elicitation.py
index ab2c9ad6a..2cfcbcb3c 100644
--- a/src/mcp/server/elicitation.py
+++ b/src/mcp/server/elicitation.py
@@ -4,7 +4,7 @@
 
 import types
 from collections.abc import Sequence
-from enum import Enum, StrEnum
+from enum import Enum
 from typing import Generic, Literal, TypeVar, Union, get_args, get_origin
 
 from pydantic import BaseModel
@@ -47,7 +47,7 @@ class AcceptedUrlElicitation(BaseModel):
 
 
 # Primitive types allowed in elicitation schemas
-_ELICITATION_PRIMITIVE_TYPES = (str, int, float, bool, StrEnum)
+_ELICITATION_PRIMITIVE_TYPES = (str, int, float, bool, Enum)
 
 
 def _validate_elicitation_schema(schema: type[BaseModel]) -> None:
diff --git a/tests/server/fastmcp/test_elicitation.py b/tests/server/fastmcp/test_elicitation.py
index 6ca0a63ba..5d3b1a29a 100644
--- a/tests/server/fastmcp/test_elicitation.py
+++ b/tests/server/fastmcp/test_elicitation.py
@@ -2,7 +2,7 @@
 Test the elicitation feature using stdio transport.
 """
 
-from enum import StrEnum
+from enum import Enum
 from typing import Any
 
 import pytest
@@ -149,7 +149,7 @@ async def elicitation_callback(
             assert field_name in result.content[0].text
 
     # Test valid Enum types (should not fail validation)
-    class Status(StrEnum):
+    class Status(str, Enum):
         ACTIVE = "active"
         INACTIVE = "inactive"
 

From d04ba8c5faa88177beb9f2755726f2b973893e2a Mon Sep 17 00:00:00 2001
From: Vincent <0426vincent@gmail.com>
Date: Fri, 19 Dec 2025 10:14:51 -0800
Subject: [PATCH 3/3] fix: Add explicit type check

---
 src/mcp/server/elicitation.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mcp/server/elicitation.py b/src/mcp/server/elicitation.py
index 2cfcbcb3c..553766811 100644
--- a/src/mcp/server/elicitation.py
+++ b/src/mcp/server/elicitation.py
@@ -101,7 +101,7 @@ def _is_primitive_field(annotation: type) -> bool:
         )
 
     # Handle Enum types
-    if issubclass(annotation, str) and issubclass(annotation, Enum):
+    if isinstance(annotation, type) and issubclass(annotation, str) and issubclass(annotation, Enum):  # type: ignore[arg-type]
         return True
 
     return False