diff --git a/custom-models/bedrock-fine-tuning/nova/understanding/dataset_validation/nova_ft_dataset_validator.py b/custom-models/bedrock-fine-tuning/nova/understanding/dataset_validation/nova_ft_dataset_validator.py
index c4489c9a8..4ac272d22 100644
--- a/custom-models/bedrock-fine-tuning/nova/understanding/dataset_validation/nova_ft_dataset_validator.py
+++ b/custom-models/bedrock-fine-tuning/nova/understanding/dataset_validation/nova_ft_dataset_validator.py
@@ -1,16 +1,30 @@
 import argparse
 import json
 import re
-
-from pydantic import BaseModel, ValidationError, ValidationInfo, field_validator, model_validator
 from typing import List, Optional
 
+from pydantic import BaseModel, ValidationError, ValidationInfo, field_validator, model_validator
 
 IMAGE_FORMATS = ["jpeg", "png", "gif", "webp"]
 VIDEO_FORMATS = ["mov", "mkv", "mp4", "webm"]
 MAX_NUM_IMAGES = 10
 MODEL_TO_NUM_SAMPLES_MAP = {"micro": (8, 20000), "lite": (8, 20000), "pro": (8, 20000)}
 
+INVALID_TOKENS_TEXT = [
+    "System:",
+    "SYSTEM:",
+    "User:",
+    "USER:",
+    "Bot:",
+    "BOT:",
+    "Assistant:",
+    "ASSISTANT:",
+    "Thought:",
+    "[EOS]",
+    "<image>",
+    "<video>",
+]
+
 
 class ConverseRoles:
     """Defines the possible roles in a conversation according to converse format"""
@@ -29,10 +43,13 @@ class NovaClientError(ValueError):
     def __init__(self, message):
         super().__init__(message)
 
+
 class NovaInternalError(Exception):
     """Base exception for Nova Fine Tuning validation errors"""
+
     pass
 
+
 def check_jsonl_file(file_path):
     """Validates that the input file has a .jsonl extension."""
     if not file_path.endswith(".jsonl"):
@@ -67,7 +84,7 @@ class S3Location(BaseModel):
     def validate_format(cls, uri):
         """Validates that the URI starts with 's3://'."""
         if not uri.startswith("s3://"):
-            raise ValueError(f"Invalid S3 URI, must start with 's3://'")
+            raise ValueError("Invalid S3 URI, must start with 's3://'")
         is_valid_path(uri.replace("s3://", ""))
         return uri
 
@@ -122,6 +139,14 @@ def validate_model_fields(cls, values):
             )
         return values
 
+    @field_validator("text")
+    def validate_text(cls, text: str):
+        if not text:
+            return text
+
+        validate_invalid_tokens(text)
+        return text
+
 
 class Message(BaseModel):
     """Represents a conversation message with role and content."""
@@ -207,6 +232,14 @@ class SystemMessage(BaseModel):
 
     text: str
 
+    @field_validator("text")
+    def validate_text(cls, text: str):
+        if not text:
+            return text
+
+        validate_invalid_tokens(text)
+        return text
+
 
 class ConverseDatasetSample(BaseModel):
     """Represents a complete conversation sample with system message and message turns."""
@@ -224,41 +257,68 @@ def validate_data_sample_rules(cls, messages):
 
 def validate_converse_dataset(args):
     """Validates the entire conversation dataset against Nova format requirements."""
-    samples = load_jsonl_data(args.input_file)
-    num_samples = len(samples)
-    validate_data_record_bounds(num_samples, args.model_name)
+    try:
+        samples = load_jsonl_data(args.input_file)
+        num_samples = len(samples)
+        print(f"Loaded {num_samples} samples from {args.input_file}")
+        validate_data_record_bounds(num_samples, args.model_name)
+    except Exception as e:
+        print(f"Error loading or validating file bounds: {e}")
+        raise
 
     error_message = ""
     failed_samples_id_list = []
 
+    print(f"Validating samples for model: {args.model_name}")
     for i, sample in enumerate(samples):
         try:
             ConverseDatasetSample.model_validate(sample, context={"model_name": args.model_name})
         except ValidationError as e:
             failed_samples_id_list.append(i)
-            error_message += f"Sample {i} - "
+            error_message += f"\nSample {i}:\n"
             for err in e.errors():
                 err["msg"] = err["msg"].replace("Value error, ", "")
-                sample_error_message = f"{err['loc']}: {err['msg']} (type={err['type']}). "
+                sample_error_message = (
+                    f"  - Location {err['loc']}: {err['msg']} (type={err['type']})\n"
+                )
                 error_message += sample_error_message
         except Exception as e:
-            raise NovaInternalError(f"Error occured: {e}")
+            raise NovaInternalError(f"Unexpected error occurred in sample {i}: {e}")
 
     if error_message:
-        prefix_str = f"Problematic samples: "
 
         if len(failed_samples_id_list) > 3:
             first_sample_id = failed_samples_id_list[0]
             second_sample_id = failed_samples_id_list[1]
             last_sample_id = failed_samples_id_list[-1]
-            failed_samples_str = f"[{first_sample_id}, {second_sample_id}, ...{last_sample_id}]. "
+            failed_samples_str = f"[{first_sample_id}, {second_sample_id}, ...{last_sample_id}]"
         else:
-            failed_samples_str = f"{failed_samples_id_list}. "
+            failed_samples_str = f"{failed_samples_id_list}"
 
-        final_err_msg = prefix_str + failed_samples_str + error_message
+        final_err_msg = (
+            f"Validation failed for samples: {failed_samples_str}\n\n"
+            f"Note: Sample IDs are zero-indexed.\n"
+            f"{error_message}"
+        )
         raise NovaClientError(final_err_msg)
     else:
-        print("Validation successful, all samples passed")
+        print("Validation successful, all samples passed!")
+
+
+def validate_invalid_tokens(text: str):
+    """Validates that the input text does not contain any disallowed tokens"""
+
+    stripped_text = text.strip()
+    client_invalid_tokens = []
+    for invalid_token in INVALID_TOKENS_TEXT:
+        if invalid_token in stripped_text:
+            client_invalid_tokens.append(f"`{invalid_token}`")
+
+    if client_invalid_tokens:
+        client_invalid_tokens_str = ", ".join(client_invalid_tokens)
+        raise ValueError(
+            f"Invalid text content, following tokens are invalid: {client_invalid_tokens_str}. Please check documentation for other invalid tokens"
+        )
 
 
 def check_roles_order(messages):
@@ -289,7 +349,7 @@ def is_valid_path(file_path):
     pattern = r"^[\w\-/\.]+$"
     if not re.match(pattern, file_path):
         raise ValueError(
-            f"Invalid characters in 'uri'. Only alphanumeric, underscores, hyphens, slashes, and dots are allowed"
+            "Invalid characters in 'uri'. Only alphanumeric, underscores, hyphens, slashes, and dots are allowed"
         )