diff --git a/api/core/app/app_config/entities.py b/api/core/app/app_config/entities.py
index 307af3747c..13c51529cc 100644
--- a/api/core/app/app_config/entities.py
+++ b/api/core/app/app_config/entities.py
@@ -1,4 +1,3 @@
-import json
 from collections.abc import Sequence
 from enum import StrEnum, auto
 from typing import Any, Literal
@@ -121,7 +120,7 @@ class VariableEntity(BaseModel):
     allowed_file_types: Sequence[FileType] | None = Field(default_factory=list)
     allowed_file_extensions: Sequence[str] | None = Field(default_factory=list)
     allowed_file_upload_methods: Sequence[FileTransferMethod] | None = Field(default_factory=list)
-    json_schema: str | None = Field(default=None)
+    json_schema: dict | None = Field(default=None)
 
     @field_validator("description", mode="before")
     @classmethod
@@ -135,17 +134,11 @@ class VariableEntity(BaseModel):
 
     @field_validator("json_schema")
     @classmethod
-    def validate_json_schema(cls, schema: str | None) -> str | None:
+    def validate_json_schema(cls, schema: dict | None) -> dict | None:
         if schema is None:
             return None
-
         try:
-            json_schema = json.loads(schema)
-        except json.JSONDecodeError:
-            raise ValueError(f"invalid json_schema value {schema}")
-
-        try:
-            Draft7Validator.check_schema(json_schema)
+            Draft7Validator.check_schema(schema)
         except SchemaError as e:
             raise ValueError(f"Invalid JSON schema: {e.message}")
         return schema
diff --git a/api/core/app/apps/advanced_chat/app_config_manager.py b/api/core/app/apps/advanced_chat/app_config_manager.py
index e4b308a6f6..c21c494efe 100644
--- a/api/core/app/apps/advanced_chat/app_config_manager.py
+++ b/api/core/app/apps/advanced_chat/app_config_manager.py
@@ -26,7 +26,6 @@ class AdvancedChatAppConfigManager(BaseAppConfigManager):
     @classmethod
     def get_app_config(cls, app_model: App, workflow: Workflow) -> AdvancedChatAppConfig:
         features_dict = workflow.features_dict
-
         app_mode = AppMode.value_of(app_model.mode)
         app_config = AdvancedChatAppConfig(
             tenant_id=app_model.tenant_id,
diff --git a/api/core/app/apps/base_app_generator.py b/api/core/app/apps/base_app_generator.py
index a6aace168e..e4486e892c 100644
--- a/api/core/app/apps/base_app_generator.py
+++ b/api/core/app/apps/base_app_generator.py
@@ -1,4 +1,3 @@
-import json
 from collections.abc import Generator, Mapping, Sequence
 from typing import TYPE_CHECKING, Any, Union, final
 
@@ -76,12 +75,24 @@ class BaseAppGenerator:
         user_inputs = {**user_inputs, **files_inputs, **file_list_inputs}
 
         # Check if all files are converted to File
-        if any(filter(lambda v: isinstance(v, dict), user_inputs.values())):
-            raise ValueError("Invalid input type")
-        if any(
-            filter(lambda v: isinstance(v, dict), filter(lambda item: isinstance(item, list), user_inputs.values()))
-        ):
-            raise ValueError("Invalid input type")
+        invalid_dict_keys = [
+            k
+            for k, v in user_inputs.items()
+            if isinstance(v, dict)
+            and entity_dictionary[k].type not in {VariableEntityType.FILE, VariableEntityType.JSON_OBJECT}
+        ]
+        if invalid_dict_keys:
+            raise ValueError(f"Invalid input type for {invalid_dict_keys}")
+
+        invalid_list_dict_keys = [
+            k
+            for k, v in user_inputs.items()
+            if isinstance(v, list)
+            and any(isinstance(item, dict) for item in v)
+            and entity_dictionary[k].type != VariableEntityType.FILE_LIST
+        ]
+        if invalid_list_dict_keys:
+            raise ValueError(f"Invalid input type for {invalid_list_dict_keys}")
 
         return user_inputs
 
@@ -178,12 +189,8 @@ class BaseAppGenerator:
                     elif value == 0:
                         value = False
             case VariableEntityType.JSON_OBJECT:
-                if not isinstance(value, str):
-                    raise ValueError(f"{variable_entity.variable} in input form must be a string")
-                try:
-                    json.loads(value)
-                except json.JSONDecodeError:
-                    raise ValueError(f"{variable_entity.variable} in input form must be a valid JSON object")
+                if not isinstance(value, dict):
+                    raise ValueError(f"{variable_entity.variable} in input form must be a dict")
             case _:
                 raise AssertionError("this statement should be unreachable.")
 
diff --git a/api/core/workflow/nodes/start/start_node.py b/api/core/workflow/nodes/start/start_node.py
index 36fc5078c5..53c1b4ee6b 100644
--- a/api/core/workflow/nodes/start/start_node.py
+++ b/api/core/workflow/nodes/start/start_node.py
@@ -1,4 +1,3 @@
-import json
 from typing import Any
 
 from jsonschema import Draft7Validator, ValidationError
@@ -43,25 +42,22 @@ class StartNode(Node[StartNodeData]):
             if value is None and variable.required:
                 raise ValueError(f"{key} is required in input form")
 
+            # If no value provided, skip further processing for this key
+            if not value:
+                continue
+
+            if not isinstance(value, dict):
+                raise ValueError(f"JSON object for '{key}' must be an object")
+
+            # Overwrite with normalized dict to ensure downstream consistency
+            node_inputs[key] = value
+
+            # If schema exists, then validate against it
             schema = variable.json_schema
             if not schema:
                 continue
 
-            if not value:
-                continue
-
             try:
-                json_schema = json.loads(schema)
-            except json.JSONDecodeError as e:
-                raise ValueError(f"{schema} must be a valid JSON object")
-
-            try:
-                json_value = json.loads(value)
-            except json.JSONDecodeError as e:
-                raise ValueError(f"{value} must be a valid JSON object")
-
-            try:
-                Draft7Validator(json_schema).validate(json_value)
+                Draft7Validator(schema).validate(value)
             except ValidationError as e:
                 raise ValueError(f"JSON object for '{key}' does not match schema: {e.message}")
-            node_inputs[key] = json_value
diff --git a/api/tests/unit_tests/core/workflow/nodes/test_start_node_json_object.py b/api/tests/unit_tests/core/workflow/nodes/test_start_node_json_object.py
index 539e72edb5..16b432bae6 100644
--- a/api/tests/unit_tests/core/workflow/nodes/test_start_node_json_object.py
+++ b/api/tests/unit_tests/core/workflow/nodes/test_start_node_json_object.py
@@ -58,6 +58,8 @@ def test_json_object_valid_schema():
         }
     )
 
+    schema = json.loads(schema)
+
     variables = [
         VariableEntity(
             variable="profile",
@@ -68,7 +70,7 @@ def test_json_object_valid_schema():
         )
     ]
 
-    user_inputs = {"profile": json.dumps({"age": 20, "name": "Tom"})}
+    user_inputs = {"profile": {"age": 20, "name": "Tom"}}
 
     node = make_start_node(user_inputs, variables)
     result = node._run()
@@ -87,6 +89,8 @@ def test_json_object_invalid_json_string():
             "required": ["age", "name"],
         }
     )
+
+    schema = json.loads(schema)
     variables = [
         VariableEntity(
             variable="profile",
@@ -97,12 +101,12 @@ def test_json_object_invalid_json_string():
         )
     ]
 
-    # Missing closing brace makes this invalid JSON
+    # Providing a string instead of an object should raise a type error
     user_inputs = {"profile": '{"age": 20, "name": "Tom"'}
 
     node = make_start_node(user_inputs, variables)
 
-    with pytest.raises(ValueError, match='{"age": 20, "name": "Tom" must be a valid JSON object'):
+    with pytest.raises(ValueError, match="JSON object for 'profile' must be an object"):
         node._run()
 
 
@@ -118,6 +122,8 @@ def test_json_object_does_not_match_schema():
         }
     )
 
+    schema = json.loads(schema)
+
     variables = [
         VariableEntity(
             variable="profile",
@@ -129,7 +135,7 @@ def test_json_object_does_not_match_schema():
     ]
 
     # age is a string, which violates the schema (expects number)
-    user_inputs = {"profile": json.dumps({"age": "twenty", "name": "Tom"})}
+    user_inputs = {"profile": {"age": "twenty", "name": "Tom"}}
 
     node = make_start_node(user_inputs, variables)
 
@@ -149,6 +155,8 @@ def test_json_object_missing_required_schema_field():
         }
     )
 
+    schema = json.loads(schema)
+
     variables = [
         VariableEntity(
             variable="profile",
@@ -160,7 +168,7 @@ def test_json_object_missing_required_schema_field():
     ]
 
     # Missing required field "name"
-    user_inputs = {"profile": json.dumps({"age": 20})}
+    user_inputs = {"profile": {"age": 20}}
 
     node = make_start_node(user_inputs, variables)
 
diff --git a/web/app/components/app/configuration/config-var/config-modal/index.tsx b/web/app/components/app/configuration/config-var/config-modal/index.tsx
index 782744882e..5ffa87375c 100644
--- a/web/app/components/app/configuration/config-var/config-modal/index.tsx
+++ b/web/app/components/app/configuration/config-var/config-modal/index.tsx
@@ -83,7 +83,7 @@ const ConfigModal: FC<IConfigModalProps> = ({
     if (!isJsonObject || !tempPayload.json_schema)
       return ''
     try {
-      return JSON.stringify(JSON.parse(tempPayload.json_schema), null, 2)
+      return tempPayload.json_schema
     }
     catch {
       return ''
diff --git a/web/app/components/base/chat/chat/utils.ts b/web/app/components/base/chat/chat/utils.ts
index ab150f3e61..a64c8162dc 100644
--- a/web/app/components/base/chat/chat/utils.ts
+++ b/web/app/components/base/chat/chat/utils.ts
@@ -37,7 +37,7 @@ export const getProcessedInputs = (inputs: Record<string, any>, inputsForm: Inpu
       return
     }
 
-    if (!inputValue)
+    if (inputValue == null)
       return
 
     if (item.type === InputVarType.singleFile) {
@@ -52,6 +52,20 @@ export const getProcessedInputs = (inputs: Record<string, any>, inputsForm: Inpu
       else
         processedInputs[item.variable] = getProcessedFiles(inputValue)
     }
+    else if (item.type === InputVarType.jsonObject) {
+      // Prefer sending an object if the user entered valid JSON; otherwise keep the raw string.
+      try {
+        const v = typeof inputValue === 'string' ? JSON.parse(inputValue) : inputValue
+        if (v && typeof v === 'object' && !Array.isArray(v))
+          processedInputs[item.variable] = v
+        else
+          processedInputs[item.variable] = inputValue
+      }
+      catch {
+        // keep original string; backend will parse/validate
+        processedInputs[item.variable] = inputValue
+      }
+    }
   })
 
   return processedInputs
diff --git a/web/app/components/share/text-generation/run-once/index.tsx b/web/app/components/share/text-generation/run-once/index.tsx
index 6094147bbd..b8193fd944 100644
--- a/web/app/components/share/text-generation/run-once/index.tsx
+++ b/web/app/components/share/text-generation/run-once/index.tsx
@@ -195,7 +195,7 @@ const RunOnce: FC<IRunOnceProps> = ({
                         noWrapper
                         className="bg h-[80px] overflow-y-auto rounded-[10px] bg-components-input-bg-normal p-1"
                         placeholder={
-                          <div className="whitespace-pre">{item.json_schema}</div>
+                          <div className="whitespace-pre">{typeof item.json_schema === 'string' ? item.json_schema : JSON.stringify(item.json_schema || '', null, 2)}</div>
                         }
                       />
                     )}
diff --git a/web/app/components/workflow/nodes/_base/components/before-run-form/form-item.tsx b/web/app/components/workflow/nodes/_base/components/before-run-form/form-item.tsx
index 81a8453582..3eef34bd7b 100644
--- a/web/app/components/workflow/nodes/_base/components/before-run-form/form-item.tsx
+++ b/web/app/components/workflow/nodes/_base/components/before-run-form/form-item.tsx
@@ -48,6 +48,12 @@ const FormItem: FC<Props> = ({
   const { t } = useTranslation()
   const { type } = payload
   const fileSettings = useHooksStore(s => s.configsMap?.fileSettings)
+  const jsonSchemaPlaceholder = React.useMemo(() => {
+    const schema = (payload as any)?.json_schema
+    if (!schema)
+      return ''
+    return typeof schema === 'string' ? schema : JSON.stringify(schema, null, 2)
+  }, [payload])
 
   const handleArrayItemChange = useCallback((index: number) => {
     return (newValue: any) => {
@@ -211,7 +217,7 @@ const FormItem: FC<Props> = ({
             noWrapper
             className="bg h-[80px] overflow-y-auto rounded-[10px] bg-components-input-bg-normal p-1"
             placeholder={
-              <div className="whitespace-pre">{payload.json_schema}</div>
+              <div className="whitespace-pre">{jsonSchemaPlaceholder}</div>
             }
           />
         )}
diff --git a/web/app/components/workflow/nodes/_base/components/variable/utils.ts b/web/app/components/workflow/nodes/_base/components/variable/utils.ts
index 9f77be0ce2..e5e8174456 100644
--- a/web/app/components/workflow/nodes/_base/components/variable/utils.ts
+++ b/web/app/components/workflow/nodes/_base/components/variable/utils.ts
@@ -353,7 +353,7 @@ const formatItem = (
         try {
           if (type === VarType.object && v.json_schema) {
             varRes.children = {
-              schema: JSON.parse(v.json_schema),
+              schema: typeof v.json_schema === 'string' ? JSON.parse(v.json_schema) : v.json_schema,
             }
           }
         }
diff --git a/web/app/components/workflow/types.ts b/web/app/components/workflow/types.ts
index 740f1c1113..63a66eb5cd 100644
--- a/web/app/components/workflow/types.ts
+++ b/web/app/components/workflow/types.ts
@@ -223,7 +223,7 @@ export type InputVar = {
   getVarValueFromDependent?: boolean
   hide?: boolean
   isFileItem?: boolean
-  json_schema?: string // for jsonObject type
+  json_schema?: string | Record<string, any> // for jsonObject type
 } & Partial<UploadFileSetting>
 
 export type ModelConfig = {
diff --git a/web/models/debug.ts b/web/models/debug.ts
index 5290268fe9..73d0910e82 100644
--- a/web/models/debug.ts
+++ b/web/models/debug.ts
@@ -62,7 +62,7 @@ export type PromptVariable = {
   icon?: string
   icon_background?: string
   hide?: boolean // used in frontend to hide variable
-  json_schema?: string
+  json_schema?: string | Record<string, any>
 }
 
 export type CompletionParams = {
diff --git a/web/service/workflow-payload.ts b/web/service/workflow-payload.ts
index b294141cb7..5e2cdebdb3 100644
--- a/web/service/workflow-payload.ts
+++ b/web/service/workflow-payload.ts
@@ -66,7 +66,30 @@ export const sanitizeWorkflowDraftPayload = (params: WorkflowDraftSyncParams): W
   if (!graph?.nodes?.length)
     return params
 
-  const sanitizedNodes = graph.nodes.map(node => sanitizeTriggerPluginNode(node as Node<TriggerPluginNodePayload>))
+  const sanitizedNodes = graph.nodes.map((node) => {
+    // First sanitize known node types (TriggerPlugin)
+    const n = sanitizeTriggerPluginNode(node as Node<TriggerPluginNodePayload>) as Node<any>
+
+    // Normalize Start node variable json_schema: ensure dict, not string
+    if ((n.data as any)?.type === BlockEnum.Start && Array.isArray((n.data as any).variables)) {
+      const next = { ...n, data: { ...n.data } }
+      next.data.variables = (n.data as any).variables.map((v: any) => {
+        if (v && v.type === 'json_object' && typeof v.json_schema === 'string') {
+          try {
+            const obj = JSON.parse(v.json_schema)
+            return { ...v, json_schema: obj }
+          }
+          catch {
+            return v
+          }
+        }
+        return v
+      })
+      return next
+    }
+
+    return n
+  })
 
   return {
     ...params,
@@ -126,7 +149,25 @@ export const hydrateWorkflowDraftResponse = (draft: FetchWorkflowDraftResponse):
           if (node.data)
             removeTempProperties(node.data as Record<string, unknown>)
 
-          return hydrateTriggerPluginNode(node)
+          let n = hydrateTriggerPluginNode(node)
+          // Normalize Start node variable json_schema to object when loading
+          if ((n.data as any)?.type === BlockEnum.Start && Array.isArray((n.data as any).variables)) {
+            const next = { ...n, data: { ...n.data } } as Node<any>
+            next.data.variables = (n.data as any).variables.map((v: any) => {
+              if (v && v.type === 'json_object' && typeof v.json_schema === 'string') {
+                try {
+                  const obj = JSON.parse(v.json_schema)
+                  return { ...v, json_schema: obj }
+                }
+                catch {
+                  return v
+                }
+              }
+              return v
+            })
+            n = next
+          }
+          return n
         })
     }
 
diff --git a/web/service/workflow.ts b/web/service/workflow.ts
index 7571e804a9..3a37db791b 100644
--- a/web/service/workflow.ts
+++ b/web/service/workflow.ts
@@ -9,6 +9,7 @@ import type {
 } from '@/types/workflow'
 import { get, post } from './base'
 import { getFlowPrefix } from './utils'
+import { sanitizeWorkflowDraftPayload } from './workflow-payload'
 
 export const fetchWorkflowDraft = (url: string) => {
   return get(url, {}, { silent: true }) as Promise<FetchWorkflowDraftResponse>
@@ -18,7 +19,8 @@ export const syncWorkflowDraft = ({ url, params }: {
   url: string
   params: Pick<FetchWorkflowDraftResponse, 'graph' | 'features' | 'environment_variables' | 'conversation_variables'>
 }) => {
-  return post<CommonResponse & { updated_at: number, hash: string }>(url, { body: params }, { silent: true })
+  const sanitized = sanitizeWorkflowDraftPayload(params)
+  return post<CommonResponse & { updated_at: number, hash: string }>(url, { body: sanitized }, { silent: true })
 }
 
 export const fetchNodesDefaultConfigs = (url: string) => {