From ddbf398892c3c1f6de4088f5848e5aad1d0a61ef Mon Sep 17 00:00:00 2001
From: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>
Date: Tue, 6 May 2025 10:38:21 -0400
Subject: [PATCH] Coerce numbers to str

---
 src/fastmcp/tools/tool.py      |  4 +++-
 src/fastmcp/utilities/types.py | 11 +++++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/fastmcp/tools/tool.py b/src/fastmcp/tools/tool.py
index fbe51130c..2bdfaac2c 100644
--- a/src/fastmcp/tools/tool.py
+++ b/src/fastmcp/tools/tool.py
@@ -127,7 +127,9 @@ class Tool(BaseModel):
                     except json.JSONDecodeError:
                         pass
 
-            type_adapter = get_cached_typeadapter(self.fn)
+            type_adapter = get_cached_typeadapter(
+                self.fn, config=frozenset([("coerce_numbers_to_str", True)])
+            )
             result = type_adapter.validate_python(parsed_args | injected_args)
             if inspect.isawaitable(result):
                 result = await result
diff --git a/src/fastmcp/utilities/types.py b/src/fastmcp/utilities/types.py
index 0ad371db3..f21a013f7 100644
--- a/src/fastmcp/utilities/types.py
+++ b/src/fastmcp/utilities/types.py
@@ -6,23 +6,26 @@ from collections.abc import Callable
 from functools import lru_cache
 from pathlib import Path
 from types import UnionType
-from typing import Annotated, TypeVar, Union, get_args, get_origin
+from typing import Annotated, Any, TypeVar, Union, get_args, get_origin
 
 from mcp.types import ImageContent
-from pydantic import TypeAdapter
+from pydantic import ConfigDict, TypeAdapter
 
 T = TypeVar("T")
 
 
 @lru_cache(maxsize=5000)
-def get_cached_typeadapter(cls: T) -> TypeAdapter[T]:
+def get_cached_typeadapter(
+    cls: T, config: frozenset[tuple[str, Any]] | None = None
+) -> TypeAdapter[T]:
     """
     TypeAdapters are heavy objects, and in an application context we'd typically
     create them once in a global scope and reuse them as often as possible.
     However, this isn't feasible for user-generated functions. Instead, we use a
     cache to minimize the cost of creating them as much as possible.
     """
-    return TypeAdapter(cls)
+    config_dict = dict(config or {})
+    return TypeAdapter(cls, config=ConfigDict(**config_dict))
 
 
 def issubclass_safe(cls: type, base: type) -> bool: