diff --git a/metagpt/actions/design_api.py b/metagpt/actions/design_api.py
index 83139035a..25b9d3720 100644
--- a/metagpt/actions/design_api.py
+++ b/metagpt/actions/design_api.py
@@ -13,7 +13,7 @@ import json
 from pathlib import Path
 from typing import Optional
 
-from metagpt.actions import Action, ActionOutput
+from metagpt.actions import Action
 from metagpt.actions.design_api_an import (
     DATA_STRUCTURES_AND_INTERFACES,
     DESIGN_API_NODE,
@@ -68,7 +68,6 @@ class WriteDesign(Action):
             logger.info("Nothing has changed.")
         # Wait until all files under `docs/system_designs/` are processed before sending the publish message,
         # leaving room for global optimization in subsequent steps.
-        return ActionOutput(content=changed_files.model_dump_json(), instruct_content=changed_files)
 
     async def _new_system_design(self, context):
         node = await DESIGN_API_NODE.fill(context=context, llm=self.llm, schema=self.prompt_schema)
diff --git a/metagpt/actions/project_management.py b/metagpt/actions/project_management.py
index 5aace9fa9..9fb4b6119 100644
--- a/metagpt/actions/project_management.py
+++ b/metagpt/actions/project_management.py
@@ -14,7 +14,6 @@ import json
 from typing import Optional
 
 from metagpt.actions.action import Action
-from metagpt.actions.action_output import ActionOutput
 from metagpt.actions.project_management_an import PM_NODE, REFINED_PM_NODE
 from metagpt.const import PACKAGE_REQUIREMENTS_FILENAME
 from metagpt.logs import logger
@@ -55,7 +54,6 @@ class WriteTasks(Action):
             logger.info("Nothing has changed.")
         # Wait until all files under `docs/tasks/` are processed before sending the publish_message, leaving room for
         # global optimization in subsequent steps.
-        return ActionOutput(content=change_files.model_dump_json(), instruct_content=change_files)
 
     async def _update_tasks(self, filename):
         system_design_doc = await self.repo.docs.system_design.get(filename)
diff --git a/metagpt/actions/write_prd.py b/metagpt/actions/write_prd.py
index 02bd1d6d5..79284530c 100644
--- a/metagpt/actions/write_prd.py
+++ b/metagpt/actions/write_prd.py
@@ -15,6 +15,7 @@ from __future__ import annotations
 
 import json
 from pathlib import Path
+from typing import Optional, Union
 
 from metagpt.actions import Action, ActionOutput
 from metagpt.actions.action_node import ActionNode
@@ -33,7 +34,7 @@ from metagpt.const import (
     REQUIREMENT_FILENAME,
 )
 from metagpt.logs import logger
-from metagpt.schema import BugFixContext, Document, Documents, Message
+from metagpt.schema import AIMessage, Document, Documents, Message
 from metagpt.utils.common import CodeParser
 from metagpt.utils.file_repository import FileRepository
 from metagpt.utils.mermaid import mermaid_to_file
@@ -66,7 +67,7 @@ class WritePRD(Action):
     3. Requirement update: If the requirement is an update, the PRD document will be updated.
     """
 
-    async def run(self, with_messages, *args, **kwargs) -> ActionOutput | Message:
+    async def run(self, with_messages, *args, **kwargs) -> Optional[Union[ActionOutput, Message]]:
         """Run the action."""
         req: Document = await self.repo.requirement
         docs: list[Document] = await self.repo.docs.prd.get_all()
@@ -82,20 +83,17 @@ class WritePRD(Action):
         # if requirement is related to other documents, update them, otherwise create a new one
         if related_docs := await self.get_related_docs(req, docs):
             logger.info(f"Requirement update detected: {req.content}")
-            return await self._handle_requirement_update(req, related_docs)
+            await self._handle_requirement_update(req, related_docs)
         else:
             logger.info(f"New requirement detected: {req.content}")
-            return await self._handle_new_requirement(req)
+            await self._handle_new_requirement(req)
 
     async def _handle_bugfix(self, req: Document) -> Message:
         # ... bugfix logic ...
         await self.repo.docs.save(filename=BUGFIX_FILENAME, content=req.content)
         await self.repo.docs.save(filename=REQUIREMENT_FILENAME, content="")
-        bug_fix = BugFixContext(filename=BUGFIX_FILENAME)
-        return Message(
-            content=bug_fix.model_dump_json(),
-            instruct_content=bug_fix,
-            role="",
+        return AIMessage(
+            content="",
             cause_by=FixBug,
             sent_from=self,
             send_to="Alex",  # the name of Engineer
diff --git a/metagpt/roles/engineer.py b/metagpt/roles/engineer.py
index e7b5cf219..0328fb28b 100644
--- a/metagpt/roles/engineer.py
+++ b/metagpt/roles/engineer.py
@@ -150,12 +150,6 @@ class Engineer(Role):
                 dependencies=list(dependencies),
                 content=coding_context.code_doc.content,
             )
-            AIMessage(
-                content=coding_context.model_dump_json(),
-                instruct_content=coding_context,
-                cause_by=WriteCode,
-            )
-
             changed_files.add(coding_context.code_doc.filename)
         if not changed_files:
             logger.info("Nothing has changed.")
@@ -177,9 +171,9 @@ class Engineer(Role):
         return await self.rc.todo.run(self.rc.history)
 
     async def _act_write_code(self):
-        changed_files = await self._act_sp_with_cr(review=self.use_code_review)
+        await self._act_sp_with_cr(review=self.use_code_review)
         return AIMessage(
-            content="\n".join(changed_files),
+            content="",
             cause_by=WriteCodeReview if self.use_code_review else WriteCode,
             send_to=self,
             sent_from=self,
@@ -221,7 +215,7 @@ class Engineer(Role):
         # The maximum number of times the 'SummarizeCode' action is automatically invoked, with -1 indicating unlimited.
         # This parameter is used for debugging the workflow.
         self.n_summarize += 1 if self.config.max_auto_summarize_code > self.n_summarize else 0
-        return AIMessage(content=json.dumps(tasks), cause_by=SummarizeCode, send_to=self, sent_from=self)
+        return AIMessage(content="", cause_by=SummarizeCode, send_to=self, sent_from=self)
 
     async def _act_code_plan_and_change(self):
         """Write code plan and change that guides subsequent WriteCode and WriteCodeReview"""
@@ -244,7 +238,7 @@ class Engineer(Role):
         )
 
         return AIMessage(
-            content=code_plan_and_change,
+            content="",
             cause_by=WriteCodePlanAndChange,
             send_to=self,
             sent_from=self,
diff --git a/metagpt/roles/qa_engineer.py b/metagpt/roles/qa_engineer.py
index c5f22174f..2947c942f 100644
--- a/metagpt/roles/qa_engineer.py
+++ b/metagpt/roles/qa_engineer.py
@@ -21,7 +21,6 @@ from metagpt.actions.summarize_code import SummarizeCode
 from metagpt.const import MESSAGE_ROUTE_TO_NONE
 from metagpt.logs import logger
 from metagpt.roles import Role
-from metagpt.utils.report import EditorReporter
 from metagpt.schema import AIMessage, Document, Message, RunCodeContext, TestingContext
 from metagpt.utils.common import (
     any_to_str,
@@ -29,6 +28,7 @@ from metagpt.utils.common import (
     init_python_folder,
     parse_recipient,
 )
+from metagpt.utils.report import EditorReporter
 
 
 class QaEngineer(Role):
diff --git a/metagpt/roles/role.py b/metagpt/roles/role.py
index b6f6b7d20..14aa7dbb5 100644
--- a/metagpt/roles/role.py
+++ b/metagpt/roles/role.py
@@ -408,7 +408,7 @@ class Role(SerializationMixin, ContextMixin, BaseModel):
         elif isinstance(response, Message):
             msg = response
         else:
-            msg = AIMessage(content=response, cause_by=self.rc.todo, sent_from=self)
+            msg = AIMessage(content=response or "", cause_by=self.rc.todo, sent_from=self)
         if self.enable_memory:
             self.rc.memory.add(msg)
 
diff --git a/metagpt/schema.py b/metagpt/schema.py
index 5fc1ae242..ba64c0f06 100644
--- a/metagpt/schema.py
+++ b/metagpt/schema.py
@@ -748,10 +748,6 @@ class CodeSummarizeContext(BaseModel):
         return hash((self.design_filename, self.task_filename))
 
 
-class BugFixContext(BaseContext):
-    filename: str = ""
-
-
 class CodePlanAndChangeContext(BaseModel):
     requirement: str = ""
     issue: str = ""