Fix : strings parameters in tool are automatically decoded when call tool

Author: gdisk

src/mcp/server/fastmcp/utilities/func_metadata.py

@@ -142,6 +142,8 @@ def pre_parse_json(self, data: dict[str, Any]) -> dict[str, Any]:
         for data_key in data.keys():
             if data_key not in key_to_field_info:
                 continue
+            if field_info.annotation is str:
+                continue # For str parameter - skip
 
             field_info = key_to_field_info[data_key]
             if isinstance(data[data_key], str) and field_info.annotation is not str: