diff --git a/rdagent/oai/backend/base.py b/rdagent/oai/backend/base.py
index 9c3f6db9..dd828880 100644
--- a/rdagent/oai/backend/base.py
+++ b/rdagent/oai/backend/base.py
@@ -11,7 +11,7 @@ from abc import ABC, abstractmethod
 from copy import deepcopy
 from datetime import datetime
 from pathlib import Path
-from typing import Any, Callable, List, Optional, Tuple, cast
+from typing import Any, Callable, List, Optional, Tuple, Type, Union, cast
 
 import pytz
 from pydantic import BaseModel, TypeAdapter
@@ -36,13 +36,14 @@ except ImportError:
 class JSONParser:
     """JSON parser supporting multiple strategies"""
 
-    def __init__(self) -> None:
+    def __init__(self, add_json_in_prompt: bool = False) -> None:
         self.strategies: List[Callable[[str], str]] = [
             self._direct_parse,
             self._extract_from_code_block,
             self._fix_python_syntax,
             self._extract_with_fix_combined,
         ]
+        self.add_json_in_prompt = add_json_in_prompt
 
     def parse(self, content: str) -> str:
         """Parse JSON content, automatically trying multiple strategies"""
@@ -55,7 +56,16 @@ class JSONParser:
                 continue
 
         # All strategies failed
-        raise json.JSONDecodeError("Failed to parse JSON after all attempts", original_content, 0)
+        if not self.add_json_in_prompt:
+            error = json.JSONDecodeError(
+                "Failed to parse JSON after all attempts, maybe because 'messages' must contain the word 'json' in some form",
+                original_content,
+                0,
+            )
+            error.message = "Failed to parse JSON after all attempts, maybe because 'messages' must contain the word 'json' in some form"  # type: ignore[attr-defined]
+            raise error
+        else:
+            raise json.JSONDecodeError("Failed to parse JSON after all attempts", original_content, 0)
 
     def _direct_parse(self, content: str) -> str:
         """Strategy 1: Direct parsing (including handling extra data)"""
@@ -528,12 +538,16 @@ class APIBackend(ABC):
         seed: Optional[int] = None,
         json_target_type: Optional[str] = None,
         add_json_in_prompt: bool = False,
+        response_format: Optional[Union[dict, Type[BaseModel]]] = None,
         **kwargs: Any,
     ) -> str:
         """
         Call the chat completion function and automatically continue the conversation if the finish_reason is length.
         """
 
+        if response_format is None and json_mode:
+            response_format = {"type": "json_object"}
+
         # 0) return directly if cache is hit
         if seed is None and LLM_SETTINGS.use_auto_chat_cache_seed_gen:
             seed = LLM_CACHE_SEED_GEN.get_next_seed()
@@ -555,11 +569,11 @@ class APIBackend(ABC):
         # Loop to get a full response
         try_n = 6
         for _ in range(try_n):  # for some long code, 3 times may not enough for reasoning models
-            if json_mode and add_json_in_prompt:
+            if response_format == {"type": "json_object"} and add_json_in_prompt:
                 self._add_json_in_prompt(new_messages)
             response, finish_reason = self._create_chat_completion_inner_function(
                 messages=new_messages,
-                json_mode=json_mode,
+                response_format=response_format,
                 **kwargs,
             )
             all_response += response
@@ -571,21 +585,31 @@ class APIBackend(ABC):
 
         # 2) refine the response and return
         if LLM_SETTINGS.reasoning_think_rm:
+            # Strategy 1: Try to match complete <think>...</think> pattern
             match = re.search(r"<think>(.*?)</think>(.*)", all_response, re.DOTALL)
-            _, all_response = match.groups() if match else ("", all_response)
+            if match:
+                _, all_response = match.groups()
+            else:
+                # Strategy 2: If no complete match, try to match only </think>
+                match = re.search(r"</think>(.*)", all_response, re.DOTALL)
+                if match:
+                    all_response = match.group(1)
+                # If no match at all, keep original content
 
         # 3) format checking
-        if json_mode or json_target_type:
-            parser = JSONParser()
+        if response_format == {"type": "json_object"} or json_target_type:
+            parser = JSONParser(add_json_in_prompt=add_json_in_prompt)
             all_response = parser.parse(all_response)
             if json_target_type:
                 # deepseek will enter this branch
                 TypeAdapter(json_target_type).validate_json(all_response)
 
-        if (response_format := kwargs.get("response_format")) is not None:
+        if response_format is not None:
             if not isinstance(response_format, dict) and issubclass(response_format, BaseModel):
                 # It may raise TypeError if initialization fails
                 response_format(**json.loads(all_response))
+            elif response_format == {"type": "json_object"}:
+                logger.info(f"Using OpenAI response format: {response_format}")
             else:
                 logger.warning(f"Unknown response_format: {response_format}, skipping validation.")
         if self.dump_chat_cache:
@@ -642,7 +666,7 @@ class APIBackend(ABC):
     def _create_chat_completion_inner_function(  # type: ignore[no-untyped-def] # noqa: C901, PLR0912, PLR0915
         self,
         messages: list[dict[str, Any]],
-        json_mode: bool = False,
+        response_format: Optional[Union[dict, Type[BaseModel]]] = None,
         *args,
         **kwargs,
     ) -> tuple[str, str | None]:
diff --git a/rdagent/oai/backend/deprec.py b/rdagent/oai/backend/deprec.py
index c052e281..23501729 100644
--- a/rdagent/oai/backend/deprec.py
+++ b/rdagent/oai/backend/deprec.py
@@ -12,12 +12,13 @@ import urllib.request
 import uuid
 from copy import deepcopy
 from pathlib import Path
-from typing import Any, Optional, cast
+from typing import Any, Optional, Type, Union, cast
 
 import numpy as np
 import openai
 import tiktoken
 from openai.types.chat import ChatCompletion
+from pydantic import BaseModel
 
 from rdagent.core.utils import LLM_CACHE_SEED_GEN, SingletonBaseClass, import_class
 from rdagent.log import LogColors
@@ -294,7 +295,7 @@ class DeprecBackend(APIBackend):
     def _create_chat_completion_inner_function(  # type: ignore[no-untyped-def] # noqa: C901, PLR0912, PLR0915
         self,
         messages: list[dict[str, Any]],
-        json_mode: bool = False,
+        response_format: Optional[Union[dict, Type[BaseModel]]] = None,
         add_json_in_prompt: bool = False,
         *args,
         **kwargs,
@@ -414,13 +415,14 @@ class DeprecBackend(APIBackend):
                 frequency_penalty=frequency_penalty,
                 presence_penalty=presence_penalty,
             )
-            if json_mode:
-                if add_json_in_prompt:
-                    for message in messages[::-1]:
-                        message["content"] = message["content"] + "\nPlease respond in json format."
-                        if message["role"] == LLM_SETTINGS.system_prompt_role:
-                            # NOTE: assumption: systemprompt is always the first message
-                            break
+
+            # FIX what if the model does not support response_schema
+            if response_format == {"type": "json_object"} and add_json_in_prompt:
+                for message in messages[::-1]:
+                    message["content"] = message["content"] + "\nPlease respond in json format."
+                    if message["role"] == LLM_SETTINGS.system_prompt_role:
+                        # NOTE: assumption: systemprompt is always the first message
+                        break
                 call_kwargs["response_format"] = {"type": "json_object"}
             response = self.chat_client.chat.completions.create(**call_kwargs)
 
diff --git a/rdagent/oai/backend/litellm.py b/rdagent/oai/backend/litellm.py
index f3740ef9..b5d1e759 100644
--- a/rdagent/oai/backend/litellm.py
+++ b/rdagent/oai/backend/litellm.py
@@ -1,5 +1,5 @@
 import copyreg
-from typing import Any, Literal, cast
+from typing import Any, Literal, Optional, Type, Union, cast
 
 import numpy as np
 from litellm import (
@@ -11,6 +11,7 @@ from litellm import (
     supports_response_schema,
     token_counter,
 )
+from pydantic import BaseModel
 
 from rdagent.log import LogColors
 from rdagent.log import rdagent_logger as logger
@@ -86,23 +87,24 @@ class LiteLLMAPIBackend(APIBackend):
     def _create_chat_completion_inner_function(  # type: ignore[no-untyped-def] # noqa: C901, PLR0912, PLR0915
         self,
         messages: list[dict[str, Any]],
-        json_mode: bool = False,
+        response_format: Optional[Union[dict, Type[BaseModel]]] = None,
         *args,
         **kwargs,
     ) -> tuple[str, str | None]:
         """
         Call the chat completion function
         """
-        if json_mode and supports_response_schema(model=LITELLM_SETTINGS.chat_model):
-            kwargs["response_format"] = {"type": "json_object"}
 
-        elif not supports_response_schema(model=LITELLM_SETTINGS.chat_model) and "response_format" in kwargs:
+        if response_format and not supports_response_schema(model=LITELLM_SETTINGS.chat_model):
             # Deepseek will enter this branch
             logger.warning(
                 f"{LogColors.RED}Model {LITELLM_SETTINGS.chat_model} does not support response schema, ignoring response_format argument.{LogColors.END}",
                 tag="llm_messages",
             )
-            kwargs.pop("response_format")
+            response_format = None
+
+        if response_format:
+            kwargs["response_format"] = response_format
 
         if LITELLM_SETTINGS.log_llm_chat_content:
             logger.info(self._build_log_messages(messages), tag="llm_messages")
diff --git a/rdagent/scenarios/data_science/proposal/exp_gen/prompts.yaml b/rdagent/scenarios/data_science/proposal/exp_gen/prompts.yaml
index afab2e62..6bfde778 100644
--- a/rdagent/scenarios/data_science/proposal/exp_gen/prompts.yaml
+++ b/rdagent/scenarios/data_science/proposal/exp_gen/prompts.yaml
@@ -344,5 +344,5 @@ output_format:
     Design a specific and detailed Pipeline task based on the given hypothesis. The output should be detailed enough to directly implement the corresponding code.
     The output should follow JSON format. The schema is as follows:
     {
-        "description": "A precise and comprehensive description of the main workflow script (`main.py`)",
+        "description": "A detailed, step-by-step implementation guide for `main.py` that synthesizes planned modifications and code structure into a comprehensive coding plan. Must be formatted in Markdown with level-3 headings (###) organizing logical sections, key decision points, and implementation steps. Should provide sufficient detail covering implementation flow, algorithms, data handling, and key logic points for unambiguous developer execution.",
     }
diff --git a/rdagent/scenarios/data_science/proposal/exp_gen/prompts_v2.yaml b/rdagent/scenarios/data_science/proposal/exp_gen/prompts_v2.yaml
index 5031cfdd..6dce7f31 100644
--- a/rdagent/scenarios/data_science/proposal/exp_gen/prompts_v2.yaml
+++ b/rdagent/scenarios/data_science/proposal/exp_gen/prompts_v2.yaml
@@ -355,23 +355,36 @@ task_gen:
     If you are confident in a specific value based on strong evidence, prior experiments, or clear rationale, specify the value clearly.
     {% include "scenarios.data_science.share:spec.hyperparameter" %}
 
+    
     {% if task_output_format is not none %}
-    ## [Partial Response Format 1] Task Output Format:
+
+    # Output Format
+
+    {% if not workflow_check %}
+
     {{ task_output_format }}
 
-    {% if workflow_check %}
-    # Step 2: Workflow Update
+    {% else %}
+
+    There are two steps in the task. But you should adhere to the final output format.
+
+    ## [Partial Response Format 1]
+    ### Step1: **Task Output Format** :
+    {{ task_output_format }}
+
+    ### Step 2: **Workflow Update** :
     Since components have dependencies, your second task is to update the workflow to reflect the changes made to the target component. Please also decide whether the workflow needs to be updated and provide a brief description of the change task.
     {{ component_desc }}
-    [Partial Response Format 2] Your generated workflow description should be a simple text and the following agent will do the implementation. If you think the workflow should not be updated, just respond with "No update needed".
-    {% endif %}
 
-    Your final output should strictly adhere to the following JSON format. 
+    ## [Partial Response Format 2] Your generated workflow description should be a simple text and the following agent will do the implementation. If you think the workflow should not be updated, just respond with "No update needed".
+
+    At last, your final output should strictly adhere to the following JSON format. 
     {
-      "task_design": ---The dict corresponding to task output format---,
-      {% if workflow_check %}"workflow_update": ---A string corresponding to workflow description--- {% endif %}
+      "task_design": a dict which strictly adheres to the **Task Output Format** in Step 1,
+      "workflow_update": "A string which is a precise and comprehensive description of the Workflow Update, or 'No update needed' if no changes are required."
     }
     {% endif %}
+    {% endif %}
     
   user: |-
     # Competition Scenario Description
@@ -489,3 +502,4 @@ output_format:
     }
 
 
+
diff --git a/rdagent/scenarios/data_science/proposal/exp_gen/proposal.py b/rdagent/scenarios/data_science/proposal/exp_gen/proposal.py
index 44a63847..a7cfbe14 100644
--- a/rdagent/scenarios/data_science/proposal/exp_gen/proposal.py
+++ b/rdagent/scenarios/data_science/proposal/exp_gen/proposal.py
@@ -729,11 +729,11 @@ class DSProposalV2ExpGen(ExpGen):
         else:
             component_info = get_component(hypotheses[0].component)
         data_folder_info = self.scen.processed_data_folder_description
+        workflow_check = not pipeline and hypotheses[0].component != "Workflow"
         sys_prompt = T(".prompts_v2:task_gen.system").r(
             task_output_format=component_info["task_output_format"] if not self.supports_response_schema else None,
-            # task_output_format=component_info["task_output_format"],
             component_desc=component_desc,
-            workflow_check=not pipeline and hypotheses[0].component != "Workflow",
+            workflow_check=workflow_check,
         )
         user_prompt = T(".prompts_v2:task_gen.user").r(
             scenario_desc=scenario_desc,
@@ -743,37 +743,47 @@ class DSProposalV2ExpGen(ExpGen):
             failed_exp_and_feedback_list_desc=failed_exp_feedback_list_desc,
             eda_improvement=fb_to_sota_exp.eda_improvement if fb_to_sota_exp else None,
         )
+
         response = APIBackend().build_messages_and_create_chat_completion(
             user_prompt=user_prompt,
             system_prompt=sys_prompt,
             response_format=CodingSketch if self.supports_response_schema else {"type": "json_object"},
             json_target_type=Dict[str, str | Dict[str, str]] if not self.supports_response_schema else None,
         )
+
         task_dict = json.loads(response)
-        task_design = (
-            task_dict.get("task_design", {}) if not self.supports_response_schema else task_dict.get("sketch", {})
-        )
-        logger.info(f"Task design:\n{task_design}")
+
+        # 1) explain the response and get main task_description
+        not_found_str = f"{component_info['target_name']} description not provided"
+        if self.supports_response_schema:
+            # task_dict: {"sketch": str, ...}
+            task_desc = task_dict.get("sketch", not_found_str)
+        else:
+            if workflow_check:
+                # task_dict:  {"task_design": ...., "workflow_update": ....}
+                task_desc = task_dict.get("task_design", {}).get("description", not_found_str)
+            else:
+                # task_dict:  {"description": ....}
+                task_desc = task_dict.get("description", not_found_str)
+        # task_desc: str, a description of the task
+
+        # 2) create the main task
+        logger.info(f"Task design:\n{task_desc}")
         task_name = hypotheses[0].component
-        description = (
-            task_design
-            if isinstance(task_design, str)
-            else task_design.get("description", f"{component_info['target_name']} description not provided")
-        )
         task_class = component_info["task_class"]
         task = task_class(
             name=task_name,
-            description=description,
+            description=task_desc,
         )
-        new_workflow_desc = task_dict.get("workflow_update", "No update needed")
         exp = DSExperiment(pending_tasks_list=[[task]], hypothesis=hypotheses[0])
-        # exp.experiment_workspace.inject_code_from_folder(sota_exp.experiment_workspace.workspace_path)
         if sota_exp is not None:
             exp.experiment_workspace.inject_code_from_file_dict(sota_exp.experiment_workspace)
-        if not pipeline and new_workflow_desc != "No update needed":
+
+        # 3) create the workflow update task
+        if workflow_check:
             workflow_task = WorkflowTask(
                 name="Workflow",
-                description=new_workflow_desc,
+                description=task_dict.get("workflow_update", "No update needed"),
             )
             exp.pending_tasks_list.append([workflow_task])
         return exp
diff --git a/test/oai/test_completion.py b/test/oai/test_completion.py
index 758f55aa..abb90f1d 100644
--- a/test/oai/test_completion.py
+++ b/test/oai/test_completion.py
@@ -1,9 +1,20 @@
 import json
 import unittest
+from typing import Any, Dict, List, Union
+
+from pydantic import BaseModel, Field
 
 from rdagent.oai.llm_utils import APIBackend
 
 
+class TestPersonModel(BaseModel):
+    """This is a test Pydantic model"""
+
+    name: str = Field(description="name")
+    age: int = Field(description="age")
+    skills: List[str] = Field(description="skills")
+
+
 class TestChatCompletion(unittest.TestCase):
     def test_chat_completion(self) -> None:
         system_prompt = "You are a helpful assistant."
@@ -34,6 +45,57 @@ class TestChatCompletion(unittest.TestCase):
         assert token is not None
         assert isinstance(token, int)
 
+    def test_json_mode_with_specific_target_type(self) -> None:
+        """Test json_mode=True with specific json_target_type"""
+        system_prompt = "You are a helpful assistant. Please respond according to requirements."
+        user_prompt = "Generate programmer information including name, age, and skills list"
+
+        response = APIBackend().build_messages_and_create_chat_completion(
+            system_prompt=system_prompt,
+            user_prompt=user_prompt,
+            json_mode=True,
+            json_target_type=Dict[str, Union[str, int, List[str]]],
+        )
+
+        # Verify response format
+        assert response is not None
+        assert isinstance(response, str)
+
+        # Verify JSON format
+        parsed = json.loads(response)
+        assert isinstance(parsed, dict)
+
+    def test_response_format_with_basemodel(self) -> None:
+        """Test response_format with BaseModel (if supported)"""
+        backend = APIBackend()
+
+        system_prompt = "You are a helpful assistant. Please respond according to requirements."
+        user_prompt = "Generate programmer information including name, age, and skills list"
+
+        if backend.supports_response_schema():
+            # Use BaseModel when response_schema is supported
+            response = backend.build_messages_and_create_chat_completion(
+                system_prompt=system_prompt,
+                user_prompt=user_prompt,
+                response_format=TestPersonModel,
+            )
+        else:
+            # Use dict + json_target_type when not supported
+            response = backend.build_messages_and_create_chat_completion(
+                system_prompt=system_prompt,
+                user_prompt=user_prompt,
+                response_format={"type": "json_object"},
+                json_target_type=Dict[str, Union[str, int, List[str]]],
+            )
+
+        # Verify response format
+        assert response is not None
+        assert isinstance(response, str)
+
+        # Verify JSON format
+        parsed = json.loads(response)
+        assert isinstance(parsed, dict)
+
 
 if __name__ == "__main__":
     unittest.main()