diff --git a/backend/oasst_backend/config.py b/backend/oasst_backend/config.py
index 157845d7..92316037 100644
--- a/backend/oasst_backend/config.py
+++ b/backend/oasst_backend/config.py
@@ -138,6 +138,8 @@ class Settings(BaseSettings):
     DEBUG_SKIP_TOXICITY_CALCULATION: bool = False
     DEBUG_DATABASE_ECHO: bool = False
 
+    DUPLICATE_MESSAGE_FILTER_WINDOW_MINUTES: int = 120
+
     HUGGING_FACE_API_KEY: str = ""
 
     ROOT_TOKENS: List[str] = ["1234"]  # supply a string that can be parsed to a json list
diff --git a/backend/oasst_backend/prompt_repository.py b/backend/oasst_backend/prompt_repository.py
index 8e2c746d..01f63d26 100644
--- a/backend/oasst_backend/prompt_repository.py
+++ b/backend/oasst_backend/prompt_repository.py
@@ -1,6 +1,7 @@
 import random
+import re
 from collections import defaultdict
-from datetime import datetime
+from datetime import datetime, timedelta
 from http import HTTPStatus
 from typing import Optional
 from uuid import UUID, uuid4
@@ -9,6 +10,7 @@ import oasst_backend.models.db_payload as db_payload
 import sqlalchemy as sa
 from loguru import logger
 from oasst_backend.api.deps import FrontendUserId
+from oasst_backend.config import settings
 from oasst_backend.journal_writer import JournalWriter
 from oasst_backend.models import (
     ApiClient,
@@ -30,7 +32,7 @@ from oasst_backend.utils.database_utils import CommitMode, managed_tx_method
 from oasst_shared.exceptions import OasstError, OasstErrorCode
 from oasst_shared.schemas import protocol as protocol_schema
 from oasst_shared.schemas.protocol import SystemStats
-from oasst_shared.utils import unaware_to_utc
+from oasst_shared.utils import unaware_to_utc, utcnow
 from sqlalchemy.orm import Query
 from sqlalchemy.orm.attributes import flag_modified
 from sqlmodel import JSON, Session, and_, func, literal_column, not_, or_, text, update
@@ -188,6 +190,18 @@ class PromptRepository:
         role = None
         depth = 0
 
+        # reject whitespaces match with ^\s+$
+        if re.match(r"^\s+$", text):
+            raise OasstError("Message text is empty", OasstErrorCode.TASK_MESSAGE_TEXT_EMPTY)
+
+        # ensure message size is below the predefined limit
+        if len(text) > settings.MESSAGE_SIZE_LIMIT:
+            logger.error(f"Message size {len(text)=} exceeds size limit of {settings.MESSAGE_SIZE_LIMIT=}.")
+            raise OasstError("Message size too long.", OasstErrorCode.TASK_MESSAGE_TOO_LONG)
+
+        if self.check_users_recent_replies_for_duplicates(text):
+            raise OasstError("User recent messages have duplicates", OasstErrorCode.TASK_MESSAGE_DUPLICATED)
+
         if task.parent_message_id:
             parent_message = self.fetch_message(task.parent_message_id)
 
@@ -556,6 +570,30 @@ class PromptRepository:
             qry = qry.filter(not_(Message.deleted))
         return self._add_user_emojis_all(qry)
 
+    def check_users_recent_replies_for_duplicates(self, text: str) -> bool:
+        """
+        Checks if the user has recently replied with the same text within a given time period.
+        """
+
+        user_id = self.user_id
+        logger.debug(f"Checking for duplicate tasks for user {user_id}")
+        # messages in the past 24 hours
+        messages = (
+            self.db.query(Message)
+            .filter(Message.user_id == user_id)
+            .order_by(Message.created_date.desc())
+            .filter(
+                Message.created_date > utcnow() - timedelta(minutes=settings.DUPLICATE_MESSAGE_FILTER_WINDOW_MINUTES)
+            )
+            .all()
+        )
+        if not messages:
+            return False
+        for msg in messages:
+            if msg.text == text:
+                return True
+        return False
+
     def fetch_user_message_trees(
         self, user_id: Message.user_id, reviewed: bool = True, include_deleted: bool = False
     ) -> list[Message]:
diff --git a/backend/oasst_backend/tree_manager.py b/backend/oasst_backend/tree_manager.py
index 909bb84b..52aff24e 100644
--- a/backend/oasst_backend/tree_manager.py
+++ b/backend/oasst_backend/tree_manager.py
@@ -520,14 +520,6 @@ class TreeManager:
                 logger.info(
                     f"Frontend reports text reply to {interaction.message_id=} with {interaction.text=} by {interaction.user=}."
                 )
-
-                # ensure message size is below the predefined limit
-                if len(interaction.text) > settings.MESSAGE_SIZE_LIMIT:
-                    logger.error(
-                        f"Message size {len(interaction.text)=} exceeds size limit of {settings.MESSAGE_SIZE_LIMIT=}."
-                    )
-                    raise OasstError("Message size too long.", OasstErrorCode.TASK_MESSAGE_TOO_LONG)
-
                 # here we store the text reply in the database
                 message = pr.store_text_reply(
                     text=interaction.text,
diff --git a/oasst-shared/oasst_shared/exceptions/oasst_api_error.py b/oasst-shared/oasst_shared/exceptions/oasst_api_error.py
index 9764062e..e7f5dcd5 100644
--- a/oasst-shared/oasst_shared/exceptions/oasst_api_error.py
+++ b/oasst-shared/oasst_shared/exceptions/oasst_api_error.py
@@ -38,6 +38,8 @@ class OasstErrorCode(IntEnum):
     TASK_REQUESTED_TYPE_NOT_AVAILABLE = 1006
     TASK_AVAILABILITY_QUERY_FAILED = 1007
     TASK_MESSAGE_TOO_LONG = 1008
+    TASK_MESSAGE_DUPLICATED = 1009
+    TASK_MESSAGE_TEXT_EMPTY = 1010
 
     # 2000-3000: prompt_repository
     INVALID_FRONTEND_MESSAGE_ID = 2000