diff --git a/api/core/tools/entities/tool_entities.py b/api/core/tools/entities/tool_entities.py
index 6941ff8fa270c7..9a98b441e2c187 100644
--- a/api/core/tools/entities/tool_entities.py
+++ b/api/core/tools/entities/tool_entities.py
@@ -4,7 +4,7 @@
 from enum import Enum
 from typing import Any, Optional, Union
 
-from pydantic import BaseModel, ConfigDict, Field, ValidationInfo, field_serializer, field_validator
+from pydantic import BaseModel, ConfigDict, Field, ValidationInfo, field_serializer, field_validator, model_validator
 
 from core.entities.provider_entities import ProviderConfig
 from core.plugin.entities.parameters import (
@@ -128,12 +128,13 @@ class VariableMessage(BaseModel):
         variable_value: str = Field(..., description="The value of the variable")
         stream: bool = Field(default=False, description="Whether the variable is streamed")
 
-        @field_validator("variable_value", mode="before")
+        @model_validator(mode="before")
         @classmethod
-        def transform_variable_value(cls, value, values) -> Any:
+        def transform_variable_value(cls, values) -> Any:
             """
             Only basic types and lists are allowed.
             """
+            value = values.get("variable_value")
             if not isinstance(value, dict | list | str | int | float | bool):
                 raise ValueError("Only basic types and lists are allowed.")
 
@@ -142,7 +143,7 @@ def transform_variable_value(cls, value, values) -> Any:
                 if not isinstance(value, str):
                     raise ValueError("When 'stream' is True, 'variable_value' must be a string.")
 
-            return value
+            return values
 
         @field_validator("variable_name", mode="before")
         @classmethod