diff --git a/.changes/next-release/enhancement-ErrorMessages-78207.json b/.changes/next-release/enhancement-ErrorMessages-78207.json
new file mode 100644
index 000000000000..c935f8701ac6
--- /dev/null
+++ b/.changes/next-release/enhancement-ErrorMessages-78207.json
@@ -0,0 +1,5 @@
+{
+  "type": "enhancement",
+  "category": "Error Messages",
+  "description": "Standardize CLI error message format to use `aws: [ERROR]: <message>` prefix for consistency across all error types."
+}
diff --git a/awscli/argparser.py b/awscli/argparser.py
index 104fefdb7825..dc92e1b9f988 100644
--- a/awscli/argparser.py
+++ b/awscli/argparser.py
@@ -14,6 +14,7 @@
 import copy
 import sys
 from difflib import get_close_matches
+from awscli.errorformat import format_error_message
 
 HELP_BLURB = (
     "To see help text, you can run:\n"
@@ -113,7 +114,7 @@ def error(self, message):
         should raise an exception.
         """
         usage_message = self.format_usage()
-        error_message = f'{self.prog}: [ERROR]: {message}'
+        error_message = format_error_message(message, prog=self.prog)
         raise ArgParseException(f'{error_message}\n\n{usage_message}')
 
 
diff --git a/awscli/customizations/configure/mfalogin.py b/awscli/customizations/configure/mfalogin.py
index 885e624c45a7..638a714acf5c 100644
--- a/awscli/customizations/configure/mfalogin.py
+++ b/awscli/customizations/configure/mfalogin.py
@@ -24,6 +24,7 @@
 from awscli.customizations.commands import BasicCommand
 from awscli.customizations.configure import profile_to_section
 from awscli.customizations.configure.writer import ConfigFileWriter
+from awscli.errorformat import write_error
 
 LOG = logging.getLogger(__name__)
 
@@ -142,7 +143,7 @@ def _get_mfa_token(self):
             'None', 'mfa_token', 'MFA token code'
         )
         if not token_code:
-            sys.stderr.write("MFA token code is required\n")
+            write_error(sys.stderr, "MFA token code is required")
             return None
         return token_code
 
@@ -156,7 +157,7 @@ def _call_sts_get_session_token(self, sts_client, duration_seconds, mfa_serial,
             )
             return response
         except ClientError as e:
-            sys.stderr.write(f"An error occurred: {e}\n")
+            write_error(sys.stderr, f"An error occurred: {e}")
             return None
 
     def _resolve_mfa_serial(self, parsed_args, source_config):
@@ -167,7 +168,7 @@ def _resolve_mfa_serial(self, parsed_args, source_config):
                 'None', 'mfa_serial', 'MFA serial number or ARN'
             )
             if not mfa_serial:
-                sys.stderr.write("MFA serial number or MFA device ARN is required\n")
+                write_error(sys.stderr, "MFA serial number or MFA device ARN is required")
                 return None
         return mfa_serial
 
@@ -252,7 +253,7 @@ def _handle_interactive_prompting(self, parsed_args, duration_seconds):
                 'None', config_name, prompt_text
             )
             if not value or value == 'None':
-                sys.stderr.write(f"{prompt_text} is required\n")
+                write_error(sys.stderr, f"{prompt_text} is required")
                 return 1
             values[config_name] = value
 
diff --git a/awscli/customizations/ecs/exceptions.py b/awscli/customizations/ecs/exceptions.py
index 4ee66a51290c..f5694555f27d 100644
--- a/awscli/customizations/ecs/exceptions.py
+++ b/awscli/customizations/ecs/exceptions.py
@@ -24,26 +24,26 @@ def __init__(self, **kwargs):
 
 
 class MissingPropertyError(ECSError):
-    fmt = "Error: Resource '{resource}' must include property '{prop_name}'"
+    fmt = "Resource '{resource}' must include property '{prop_name}'"
 
 
 class FileLoadError(ECSError):
-    fmt = "Error: Unable to load file at {file_path}: {error}"
+    fmt = "Unable to load file at {file_path}: {error}"
 
 
 class InvalidPlatformError(ECSError):
-    fmt = "Error: {resource} '{name}' must support 'ECS' compute platform"
+    fmt = "{resource} '{name}' must support 'ECS' compute platform"
 
 
 class InvalidProperyError(ECSError):
     fmt = (
-        "Error: deployment group '{dg_name}' does not target "
+        "deployment group '{dg_name}' does not target "
         "ECS {resource} '{resource_name}'"
     )
 
 
 class InvalidServiceError(ECSError):
-    fmt = "Error: Service '{service}' not found in cluster '{cluster}'"
+    fmt = "Service '{service}' not found in cluster '{cluster}'"
 
 
 class ServiceClientError(ECSError):
diff --git a/awscli/customizations/emr/applicationutils.py b/awscli/customizations/emr/applicationutils.py
index 4072fc4126c8..b32563bec024 100644
--- a/awscli/customizations/emr/applicationutils.py
+++ b/awscli/customizations/emr/applicationutils.py
@@ -62,7 +62,7 @@ def build_applications(region, parsed_applications, ami_version=None):
                 )
             else:
                 raise ParamValidationError(
-                    'aws: error: AMI version %s is not '
+                    'AMI version %s is not '
                     'compatible with HBase.' % ami_version
                 )
         elif app_name == constants.IMPALA:
diff --git a/awscli/customizations/emr/createcluster.py b/awscli/customizations/emr/createcluster.py
index 4075c85a6303..a55bc5baf939 100644
--- a/awscli/customizations/emr/createcluster.py
+++ b/awscli/customizations/emr/createcluster.py
@@ -293,7 +293,7 @@ def _run_main_command(self, parsed_args, parsed_globals):
                     )
                 except ValueError:
                     raise ParamValidationError(
-                        'aws: error: invalid json argument for '
+                        'invalid json argument for '
                         'option --configurations'
                     )
 
@@ -697,7 +697,7 @@ def _build_bootstrap_actions(self, cluster, parsed_boostrap_actions):
             > constants.MAX_BOOTSTRAP_ACTION_NUMBER
         ):
             raise ParamValidationError(
-                'aws: error: maximum number of '
+                'maximum number of '
                 'bootstrap actions for a cluster exceeded.'
             )
 
diff --git a/awscli/customizations/emr/emrutils.py b/awscli/customizations/emr/emrutils.py
index ce005ce3304e..e2a4048a8700 100644
--- a/awscli/customizations/emr/emrutils.py
+++ b/awscli/customizations/emr/emrutils.py
@@ -60,7 +60,7 @@ def apply_boolean_options(
 ):
     if true_option and false_option:
         error_message = (
-            'aws: error: cannot use both '
+            'cannot use both '
             + true_option_name
             + ' and '
             + false_option_name
diff --git a/awscli/customizations/emr/exceptions.py b/awscli/customizations/emr/exceptions.py
index d1559886a498..7b3714a1de48 100644
--- a/awscli/customizations/emr/exceptions.py
+++ b/awscli/customizations/emr/exceptions.py
@@ -41,7 +41,7 @@ class MissingParametersError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: The following required parameters are missing for '
+        'The following required parameters are missing for '
         '{object_name}: {missing}.'
     )
 
@@ -53,7 +53,7 @@ class EmptyListError(EmrError, ParamValidationError):
     :ivar param: The provided list parameter
     """
 
-    fmt = 'aws: error: The prameter {param} cannot be an empty list.'
+    fmt = 'The prameter {param} cannot be an empty list.'
 
 
 class MissingRequiredInstanceGroupsError(EmrError, ParamValidationError):
@@ -63,7 +63,7 @@ class MissingRequiredInstanceGroupsError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: Must specify either --instance-groups or '
+        'Must specify either --instance-groups or '
         '--instance-type with --instance-count(optional) to '
         'configure instance groups.'
     )
@@ -77,7 +77,7 @@ class InstanceGroupsValidationError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: You may not specify --instance-type '
+        'You may not specify --instance-type '
         'or --instance-count with --instance-groups, '
         'because --instance-type and --instance-count are '
         'shortcut options for --instance-groups.'
@@ -91,7 +91,7 @@ class InvalidAmiVersionError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: The supplied AMI version "{ami_version}" is invalid.'
+        'The supplied AMI version "{ami_version}" is invalid.'
         ' Please see AMI Versions Supported in Amazon EMR in '
         'Amazon Elastic MapReduce Developer Guide: '
         'http://docs.aws.amazon.com/ElasticMapReduce/'
@@ -108,7 +108,7 @@ class MissingBooleanOptionsError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: Must specify one of the following boolean options: '
+        'Must specify one of the following boolean options: '
         '{true_option}|{false_option}.'
     )
 
@@ -120,7 +120,7 @@ class UnknownStepTypeError(EmrError, ParamValidationError):
     :ivar step_type: the step_type provided.
     """
 
-    fmt = 'aws: error: The step type {step_type} is not supported.'
+    fmt = 'The step type {step_type} is not supported.'
 
 
 class UnknownIamEndpointError(EmrError):
@@ -154,7 +154,7 @@ class LogUriError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: LogUri not specified. You must specify a logUri '
+        'LogUri not specified. You must specify a logUri '
         'if you enable debugging when creating a cluster.'
     )
 
@@ -212,7 +212,7 @@ class SubnetAndAzValidationError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: You may not specify both a SubnetId and an Availabili'
+        'You may not specify both a SubnetId and an Availabili'
         'tyZone (placement) because ec2SubnetId implies a placement.'
     )
 
@@ -222,7 +222,7 @@ class RequiredOptionsError(EmrError, ParamValidationError):
     Either of option1 or option2 is required.
     """
 
-    fmt = 'aws: error: Either {option1} or {option2} is required.'
+    fmt = 'Either {option1} or {option2} is required.'
 
 
 class MutualExclusiveOptionError(EmrError, ParamValidationError):
@@ -236,7 +236,7 @@ class MutualExclusiveOptionError(EmrError, ParamValidationError):
 
     def __init__(self, **kwargs):
         msg = (
-            'aws: error: You cannot specify both '
+            'You cannot specify both '
             + kwargs.get('option1', '')
             + ' and '
             + kwargs.get('option2', '')
@@ -256,7 +256,7 @@ class MissingApplicationsError(EmrError, ParamValidationError):
 
     def __init__(self, **kwargs):
         msg = (
-            'aws: error: Some of the steps require the following'
+            'Some of the steps require the following'
             ' applications to be installed: '
             + ', '.join(kwargs['applications'])
             + '. Please install the'
@@ -270,7 +270,7 @@ class ClusterTerminatedError(EmrError):
     The cluster is terminating or has already terminated.
     """
 
-    fmt = 'aws: error: Cluster terminating or already terminated.'
+    fmt = 'Cluster terminating or already terminated.'
 
 
 class ClusterStatesFilterValidationError(EmrError, ParamValidationError):
@@ -282,7 +282,7 @@ class ClusterStatesFilterValidationError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: You can specify only one of the cluster state '
+        'You can specify only one of the cluster state '
         'filters: --cluster-states, --active, --terminated, --failed.'
     )
 
@@ -296,7 +296,7 @@ class MissingClusterAttributesError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: Must specify one of the following boolean options: '
+        'Must specify one of the following boolean options: '
         '--visible-to-all-users|--no-visible-to-all-users, '
         '--termination-protected|--no-termination-protected, '
         '--auto-terminate|--no-auto-terminate, '
@@ -314,14 +314,14 @@ class InvalidEmrFsArgumentsError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: {parent_object_name} is not specified. Thus, '
+        '{parent_object_name} is not specified. Thus, '
         ' following parameters are invalid: {invalid}'
     )
 
 
 class DuplicateEmrFsConfigurationError(EmrError, ParamValidationError):
     fmt = (
-        'aws: error: EMRFS should be configured either using '
+        'EMRFS should be configured either using '
         '--configuration or --emrfs but not both'
     )
 
@@ -334,7 +334,7 @@ class UnknownCseProviderTypeError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: The client side encryption type "{provider_type}" is '
+        'The client side encryption type "{provider_type}" is '
         'not supported. You must specify either KMS or Custom'
     )
 
@@ -347,7 +347,7 @@ class UnknownEncryptionTypeError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: The encryption type "{encryption}" is invalid. '
+        'The encryption type "{encryption}" is invalid. '
         'You must specify either ServerSide or ClientSide'
     )
 
@@ -361,14 +361,14 @@ class BothSseAndEncryptionConfiguredError(EmrError, ParamValidationError):
     """
 
     fmt = (
-        'aws: error: Both SSE={sse} and Encryption={encryption} are '
+        'Both SSE={sse} and Encryption={encryption} are '
         'configured for --emrfs. You must specify only one of the two.'
     )
 
 
 class InvalidBooleanConfigError(EmrError, ParamValidationError):
     fmt = (
-        "aws: error: {config_value} for {config_key} in the config file is "
+        "{config_value} for {config_key} in the config file is "
         "invalid. The value should be either 'True' or 'False'. Use "
         "'aws configure set {profile_var_name}.emr.{config_key} <value>' "
         "command to set a valid value."
@@ -377,13 +377,13 @@ class InvalidBooleanConfigError(EmrError, ParamValidationError):
 
 class UnsupportedCommandWithReleaseError(EmrError, ParamValidationError):
     fmt = (
-        "aws: error: {command} is not supported with "
+        "{command} is not supported with "
         "'{release_label}' release."
     )
 
 
 class MissingAutoScalingRoleError(EmrError, ParamValidationError):
     fmt = (
-        "aws: error: Must specify --auto-scaling-role when configuring an "
+        "Must specify --auto-scaling-role when configuring an "
         "AutoScaling policy for an instance group."
     )
diff --git a/awscli/customizations/emr/hbase.py b/awscli/customizations/emr/hbase.py
index 5963b6070afb..105993b5e28a 100644
--- a/awscli/customizations/emr/hbase.py
+++ b/awscli/customizations/emr/hbase.py
@@ -129,7 +129,7 @@ def _check_type(self, type):
         type = type.lower()
         if type != constants.FULL and type != constants.INCREMENTAL:
             raise ParamValidationError(
-                'aws: error: invalid type. '
+                'invalid type. '
                 'type should be either '
                 + constants.FULL
                 + ' or '
@@ -145,7 +145,7 @@ def _check_unit(self, unit):
             and unit != constants.DAYS
         ):
             raise ParamValidationError(
-                'aws: error: invalid unit. unit should be one of'
+                'invalid unit. unit should be one of'
                 ' the following values: '
                 + constants.MINUTES
                 + ', '
diff --git a/awscli/customizations/emr/installapplications.py b/awscli/customizations/emr/installapplications.py
index 6212a6b14c99..c24cb63acc2c 100644
--- a/awscli/customizations/emr/installapplications.py
+++ b/awscli/customizations/emr/installapplications.py
@@ -67,13 +67,13 @@ def _check_for_supported_apps(self, parsed_applications):
             if app_name in constants.APPLICATIONS:
                 if app_name not in self.supported_apps:
                     raise ParamValidationError(
-                        "aws: error: " + app_config['Name'] + " cannot be"
+                        app_config['Name'] + " cannot be"
                         " installed on a running cluster. 'Name' should be one"
                         " of the following: " + ', '.join(self.supported_apps)
                     )
             else:
                 raise ParamValidationError(
-                    "aws: error: Unknown application: "
+                    "Unknown application: "
                     + app_config['Name']
                     + ". 'Name' should be one of the following: "
                     + ', '.join(constants.APPLICATIONS)
diff --git a/awscli/errorformat.py b/awscli/errorformat.py
new file mode 100644
index 000000000000..3f7e01429df9
--- /dev/null
+++ b/awscli/errorformat.py
@@ -0,0 +1,41 @@
+# Copyright 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+#     http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+
+"""
+Error message formatting module for AWS CLI.
+
+This module provides centralized error formatting functionality to ensure
+all error messages follow the standard format: aws: [ERROR]: <error-message>
+
+This standardization improves accessibility for users with visual disabilities
+and those using assistive technologies like screen readers.
+"""
+
+# Standard error prefix format for all AWS CLI error messages
+ERROR_PREFIX = "aws: [ERROR]:"
+
+
+def format_error_message(message, prog="aws"):
+    if not message:
+        return f"{prog}: [ERROR]:"
+
+    message = message.strip()
+
+    return f"{prog}: [ERROR]: {message}"
+
+
+def write_error(stderr, message):
+    formatted_message = format_error_message(message)
+    stderr.write("\n")
+    stderr.write(formatted_message)
+    stderr.write("\n")
diff --git a/awscli/errorhandler.py b/awscli/errorhandler.py
index 51d1c31f9514..9f1c2b8862c4 100644
--- a/awscli/errorhandler.py
+++ b/awscli/errorhandler.py
@@ -37,6 +37,7 @@
     ParamValidationError,
 )
 from awscli.utils import PagerInitializationException
+from awscli.errorformat import write_error
 
 LOG = logging.getLogger(__name__)
 
@@ -82,9 +83,8 @@ def handle_exception(self, exception, stdout, stderr):
                 return return_val
 
     def _do_handle_exception(self, exception, stdout, stderr):
-        stderr.write("\n")
-        stderr.write(self.MESSAGE % exception)
-        stderr.write("\n")
+        message = self.MESSAGE % exception
+        write_error(stderr, message)
         return self.RC
 
 
@@ -145,8 +145,8 @@ class UnknownArgumentErrorHandler(FilteredExceptionHandler):
 
     def _do_handle_exception(self, exception, stdout, stderr):
         stderr.write("\n")
-        stderr.write(f'usage: {USAGE}\n{exception}\n')
-        stderr.write("\n")
+        stderr.write(f'usage: {USAGE}\n')
+        write_error(stderr, str(exception))
         return self.RC
 
 
diff --git a/tests/functional/ecs/test_deploy.py b/tests/functional/ecs/test_deploy.py
index 9874ba6055e6..fe597f6235e1 100644
--- a/tests/functional/ecs/test_deploy.py
+++ b/tests/functional/ecs/test_deploy.py
@@ -501,7 +501,7 @@ def test_deploy_error_missing_appspec_property(self):
         )
 
         expected_stderr = (
-            "\nError: Resource 'properties' must "
+            "\naws: [ERROR]: Resource 'properties' must "
             "include property 'taskDefinition'\n"
         )
 
@@ -573,7 +573,7 @@ def test_deploy_error_invalid_platform(self):
         ]
 
         expected_stderr = (
-            "\nError: Application '"
+            "\naws: [ERROR]: Application '"
             + self.application_name
             + "' must support 'ECS' compute platform\n"
         )
diff --git a/tests/functional/history/test_list.py b/tests/functional/history/test_list.py
index 6391d5791bac..18b87f036ade 100644
--- a/tests/functional/history/test_list.py
+++ b/tests/functional/history/test_list.py
@@ -45,7 +45,7 @@ def test_show_nothing_when_no_history(self):
             'to the config file.'
         )
         self.assertEqual('', ensure_text_type(out))
-        self.assertEqual('\n%s\n' % error_message, ensure_text_type(err))
+        self.assertEqual('\naws: [ERROR]: %s\n' % error_message, ensure_text_type(err))
 
     def test_show_one_call_present(self):
         self.parsed_responses = [
diff --git a/tests/functional/s3/test_mv_command.py b/tests/functional/s3/test_mv_command.py
index 17ce7a5aa1f8..91eb11c85a2c 100644
--- a/tests/functional/s3/test_mv_command.py
+++ b/tests/functional/s3/test_mv_command.py
@@ -525,7 +525,7 @@ def test_get_mrap_buckets_raises_if_alias_not_found(self):
         ]
         stderr = self.run_cmd(cmdline, expected_rc=252)[1]
         self.assertEqual(
-            "\nCouldn't find multi-region access point with alias foobar.mrap "
+            "\naws: [ERROR]: Couldn't find multi-region access point with alias foobar.mrap "
             "in account 123456789012\n",
             stderr,
         )
diff --git a/tests/unit/customizations/configure/test_mfalogin.py b/tests/unit/customizations/configure/test_mfalogin.py
index 1c6ab7ba9b18..a91b809f2a0e 100644
--- a/tests/unit/customizations/configure/test_mfalogin.py
+++ b/tests/unit/customizations/configure/test_mfalogin.py
@@ -166,9 +166,8 @@ def test_no_mfa_serial_provided(self):
                         self.parsed_args, self.parsed_globals
                     )
                     self.assertEqual(rc, 1)
-                    mock_stderr.write.assert_called_with(
-                        "MFA serial number or MFA device ARN is required\n"
-                    )
+                    all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+                    self.assertIn("aws: [ERROR]: MFA serial number or MFA device ARN is required", all_writes)
 
     def test_no_token_code_provided(self):
         # Mock botocore.session.Session
@@ -188,9 +187,8 @@ def test_no_token_code_provided(self):
                         self.parsed_args, self.parsed_globals
                     )
                     self.assertEqual(rc, 1)
-                    mock_stderr.write.assert_called_with(
-                        "MFA token code is required\n"
-                    )
+                    all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+                    self.assertIn("aws: [ERROR]: MFA token code is required", all_writes)
 
     def test_sts_client_error(self):
         self.session.get_scoped_config.return_value = {}
@@ -218,9 +216,9 @@ def test_sts_client_error(self):
                 self.parsed_args, self.parsed_globals
             )
             self.assertEqual(rc, 1)
-            mock_stderr.write.assert_called_with(
-                mock.ANY
-            )  # Just check it was called
+            all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+            self.assertIn("aws: [ERROR]:", all_writes)
+            self.assertIn("An error occurred", all_writes)
 
     def test_successful_mfa_login(self):
         # Setup
@@ -448,9 +446,8 @@ def test_handle_missing_default_profile_missing_access_key(self):
             )
 
             self.assertEqual(rc, 1)
-            mock_stderr.write.assert_called_with(
-                "AWS Access Key ID is required\n"
-            )
+            all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+            self.assertIn("aws: [ERROR]: AWS Access Key ID is required", all_writes)
 
     def test_handle_missing_default_profile_missing_secret_key(self):
         """Test error when secret key is not provided."""
@@ -465,9 +462,8 @@ def test_handle_missing_default_profile_missing_secret_key(self):
             )
 
             self.assertEqual(rc, 1)
-            mock_stderr.write.assert_called_with(
-                "AWS Secret Access Key is required\n"
-            )
+            all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+            self.assertIn("aws: [ERROR]: AWS Secret Access Key is required", all_writes)
 
     def test_credential_value_prompting_clean_display(self):
         """Test that credential prompting doesn't show default values."""
@@ -515,11 +511,9 @@ def test_handle_missing_default_profile_sts_error(self):
                 )
 
                 self.assertEqual(rc, 1)
-                # Verify error message was written
-                mock_stderr.write.assert_called()
-                self.assertIn(
-                    'An error occurred', str(mock_stderr.write.call_args)
-                )
+                all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+                self.assertIn("aws: [ERROR]:", all_writes)
+                self.assertIn("An error occurred", all_writes)
 
     def test_non_interactive_missing_mfa_serial(self):
         """Test non-interactive mode when MFA serial is missing."""
@@ -539,9 +533,8 @@ def test_non_interactive_missing_mfa_serial(self):
                     )
 
                     self.assertEqual(rc, 1)
-                    mock_stderr.write.assert_called_with(
-                        "MFA serial number or MFA device ARN is required\n"
-                    )
+                    all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+                    self.assertIn("aws: [ERROR]: MFA serial number or MFA device ARN is required", all_writes)
 
     def test_non_interactive_missing_token_code(self):
         """Test non-interactive mode when token code would be prompted."""
@@ -559,9 +552,8 @@ def test_non_interactive_missing_token_code(self):
                 )
 
                 self.assertEqual(rc, 1)
-                mock_stderr.write.assert_called_with(
-                    "MFA token code is required\n"
-                )
+                all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+                self.assertIn("aws: [ERROR]: MFA token code is required", all_writes)
 
     def test_empty_credential_input_handling(self):
         """Test handling of empty credential inputs."""
@@ -573,6 +565,5 @@ def test_empty_credential_input_handling(self):
             )
 
             self.assertEqual(rc, 1)
-            mock_stderr.write.assert_called_with(
-                "AWS Access Key ID is required\n"
-            )
+            all_writes = ''.join(str(call) for call in mock_stderr.write.call_args_list)
+            self.assertIn("aws: [ERROR]: AWS Access Key ID is required", all_writes)
\ No newline at end of file
diff --git a/tests/unit/customizations/emr/__init__.py b/tests/unit/customizations/emr/__init__.py
index bd22f2a01026..635d69227c0e 100644
--- a/tests/unit/customizations/emr/__init__.py
+++ b/tests/unit/customizations/emr/__init__.py
@@ -42,6 +42,6 @@ def assert_error_msg(
         self, cmd, exception_class_name, error_msg_kwargs={}, rc=255
     ):
         exception_class = getattr(exceptions, exception_class_name)
-        error_msg = "\n%s\n" % exception_class.fmt.format(**error_msg_kwargs)
+        error_msg = "\naws: [ERROR]: %s\n" % exception_class.fmt.format(**error_msg_kwargs)
         result = self.run_cmd(cmd, rc)
         self.assertEqual(error_msg, result[1])
diff --git a/tests/unit/customizations/emr/test_add_steps.py b/tests/unit/customizations/emr/test_add_steps.py
index ea2edde91f6d..d34f494530d8 100644
--- a/tests/unit/customizations/emr/test_add_steps.py
+++ b/tests/unit/customizations/emr/test_add_steps.py
@@ -188,7 +188,7 @@ class TestAddSteps(BaseAWSCommandParamsTest):
     def test_unknown_step_type(self):
         cmd = self.prefix + 'Type=unknown'
         expected_error_msg = (
-            '\naws: error: ' + 'The step type unknown is not supported.\n'
+            '\naws: [ERROR]: ' + 'The step type unknown is not supported.\n'
         )
         self.assert_error_for_ami_and_release_based_clusters(
             cmd=cmd,
@@ -218,7 +218,7 @@ def test_default_step_type_name_action_on_failure(self):
     def test_custom_jar_step_missing_jar(self):
         cmd = self.prefix + 'Name=CustomJarMissingJar'
         expected_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for CustomJARStepConfig: Jar.\n'
         )
         self.assert_error_for_ami_and_release_based_clusters(
@@ -420,7 +420,7 @@ def test_step_with_execution_role_arn(self):
     def test_streaming_step_missing_args(self):
         cmd = self.prefix + 'Type=Streaming'
         expected_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for StreamingStepConfig: Args.\n'
         )
         self.assert_error_for_ami_and_release_based_clusters(
@@ -602,7 +602,7 @@ def test_hive_step_with_default_fields(self):
     def test_hive_step_missing_args(self):
         cmd = self.prefix + 'Type=Hive'
         expected_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for HiveStepConfig: Args.\n'
         )
 
@@ -781,7 +781,7 @@ def test_pig_step_with_default_fields(self):
     def test_pig_missing_args(self):
         cmd = self.prefix + 'Type=Pig'
         expected_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for PigStepConfig: Args.\n'
         )
         self.assert_error_for_ami_and_release_based_clusters(
@@ -973,7 +973,7 @@ def test_SPARK_SUBMIT_SCRIPT_RUNNER_STEP(self):
     def test_spark_missing_arg(self):
         cmd = self.prefix + 'Type=SPARK'
         expected_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for SparkStepConfig: Args.\n'
         )
         self.assert_error_for_ami_and_release_based_clusters(
@@ -1114,7 +1114,7 @@ def test_spark_step_with_step_monitoring_configuration_no_log_uri_or_encryption_
     def test_impala_missing_args(self):
         cmd = self.prefix + 'Type=Impala'
         expected_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for ImpalaStepConfig: Args.\n'
         )
         self.assert_error_for_ami_and_release_based_clusters(
@@ -1249,7 +1249,7 @@ def test_impala_step_with_release(self):
         test_step_config = 'Type=Impala,' + self.IMPALA_BASIC_ARGS
         cmd = self.prefix + test_step_config
         expected_result_release = (
-            '\naws: error: The step type impala ' + 'is not supported.\n'
+            '\naws: [ERROR]: The step type impala ' + 'is not supported.\n'
         )
 
         self.assert_error_for_ami_and_release_based_clusters(
@@ -1261,7 +1261,7 @@ def test_impala_step_with_release(self):
     def test_empty_step_args(self):
         cmd = self.prefix + 'Type=Streaming,Args='
         expected_error_msg = (
-            '\naws: error: The prameter Args cannot ' 'be an empty list.\n'
+            '\naws: [ERROR]: The prameter Args cannot ' 'be an empty list.\n'
         )
         self.assert_error_for_ami_and_release_based_clusters(
             cmd=cmd,
@@ -1285,7 +1285,7 @@ def test_empty_step_args(self):
 
         cmd = self.prefix + 'Args='
         expected_error_msg = (
-            '\naws: error: The following required parameters'
+            '\naws: [ERROR]: The following required parameters'
             ' are missing for CustomJARStepConfig: Jar.\n'
         )
         self.assert_error_for_ami_and_release_based_clusters(
diff --git a/tests/unit/customizations/emr/test_config.py b/tests/unit/customizations/emr/test_config.py
index 1574e0fcedd9..921e5949e85a 100644
--- a/tests/unit/customizations/emr/test_config.py
+++ b/tests/unit/customizations/emr/test_config.py
@@ -91,7 +91,7 @@ def test_with_bad_configs(self, mock_run_main_command):
     def test_with_bad_boolean_value(self):
         self.set_configs(BAD_BOOLEAN_VALUE_CONFIGS)
         cmd = CREATE_CLUSTER_CMD
-        expect_error_msg = "\n%s\n" % InvalidBooleanConfigError.fmt.format(
+        expect_error_msg = "\naws: [ERROR]: %s\n" % InvalidBooleanConfigError.fmt.format(
             config_value='False1',
             config_key='enable_debugging',
             profile_var_name='default',
diff --git a/tests/unit/customizations/emr/test_create_cluster_ami_version.py b/tests/unit/customizations/emr/test_create_cluster_ami_version.py
index e97b48393ea2..555ac052dcca 100644
--- a/tests/unit/customizations/emr/test_create_cluster_ami_version.py
+++ b/tests/unit/customizations/emr/test_create_cluster_ami_version.py
@@ -440,7 +440,7 @@ def test_mutual_exclusive_use_default_roles_and_service_role(self):
             + '--ec2-attributes InstanceProfile=Ec2_InstanceProfile'
         )
         expected_error_msg = (
-            '\naws: error: You cannot specify both --use-default-roles '
+            '\naws: [ERROR]: You cannot specify both --use-default-roles '
             'and --ec2-attributes InstanceProfile options together. Either '
             'choose --use-default-roles or use both --service-role <roleName>'
             ' and --ec2-attributes InstanceProfile=<profileName>.\n'
@@ -454,7 +454,7 @@ def test_mutual_exclusive_use_default_roles_and_instance_profile(self):
             '--ec2-attributes InstanceProfile=Ec2_InstanceProfile'
         )
         expected_error_msg = (
-            '\naws: error: You cannot specify both --use-default-roles '
+            '\naws: [ERROR]: You cannot specify both --use-default-roles '
             'and --service-role options together. Either choose '
             '--use-default-roles or use both --service-role <roleName> '
             'and --ec2-attributes InstanceProfile=<profileName>.\n'
@@ -512,7 +512,7 @@ def test_auto_terminate_and_no_auto_terminate(self):
             + '--auto-terminate --no-auto-terminate'
         )
         expected_error_msg = (
-            '\naws: error: cannot use both --no-auto-terminate and'
+            '\naws: [ERROR]: cannot use both --no-auto-terminate and'
             ' --auto-terminate options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -535,7 +535,7 @@ def test_termination_protected_and_no_termination_protected(self):
             DEFAULT_CMD + '--termination-protected --no-termination-protected'
         )
         expected_error_msg = (
-            '\naws: error: cannot use both --termination-protected'
+            '\naws: [ERROR]: cannot use both --termination-protected'
             ' and --no-termination-protected options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -565,7 +565,7 @@ def test_unhealthy_node_replacement_and_no_unhealthy_node_replacement(
             + '--unhealthy-node-replacement --no-unhealthy-node-replacement'
         )
         expected_error_msg = (
-            '\naws: error: cannot use both --unhealthy-node-replacement'
+            '\naws: [ERROR]: cannot use both --unhealthy-node-replacement'
             ' and --no-unhealthy-node-replacement options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -584,7 +584,7 @@ def test_no_visible_to_all_users(self):
     def test_visible_to_all_users_and_no_visible_to_all_users(self):
         cmd = DEFAULT_CMD + '--visible-to-all-users --no-visible-to-all-users'
         expected_error_msg = (
-            '\naws: error: cannot use both --visible-to-all-users and '
+            '\naws: [ERROR]: cannot use both --visible-to-all-users and '
             '--no-visible-to-all-users options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -605,7 +605,7 @@ def test_no_extended_support(self):
     def test_extended_support_and_no_extended_support(self):
         cmd = DEFAULT_CMD + '--extended-support --no-extended-support'
         expected_error_msg = (
-            '\naws: error: cannot use both --extended-support'
+            '\naws: [ERROR]: cannot use both --extended-support'
             ' and --no-extended-support options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -670,7 +670,7 @@ def test_enable_debugging(self):
     def test_enable_debugging_no_log_uri(self):
         cmd = DEFAULT_CMD + '--enable-debugging'
         expected_error_msg = (
-            '\naws: error: LogUri not specified. You must specify a logUri'
+            '\naws: [ERROR]: LogUri not specified. You must specify a logUri'
             ' if you enable debugging when creating a cluster.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -683,7 +683,7 @@ def test_enable_debugging_and_no_enable_debugging(self):
             + ' --log-uri s3://test/logs'
         )
         expected_error_msg = (
-            '\naws: error: cannot use both --enable-debugging and '
+            '\naws: [ERROR]: cannot use both --enable-debugging and '
             '--no-enable-debugging options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -760,7 +760,7 @@ def test_instance_groups_instance_type_and_count(self):
     def test_instance_groups_missing_required_parameter_error(self):
         cmd = 'emr create-cluster --use-default-roles --ami-version 3.0.4 '
         expect_error_msg = (
-            '\naws: error: Must specify either --instance-groups or '
+            '\naws: [ERROR]: Must specify either --instance-groups or '
             '--instance-type with --instance-count(optional) to '
             'configure instance groups.\n'
         )
@@ -772,7 +772,7 @@ def test_instance_groups_missing_required_parameter_error(self):
             '--instance-count 2'
         )
         expect_error_msg = (
-            '\naws: error: Must specify either --instance-groups or '
+            '\naws: [ERROR]: Must specify either --instance-groups or '
             '--instance-type with --instance-count(optional) to '
             'configure instance groups.\n'
         )
@@ -786,7 +786,7 @@ def test_instance_groups_exclusive_parameter_validation_error(self):
             + DEFAULT_INSTANCE_GROUPS_ARG
         )
         expect_error_msg = (
-            '\naws: error: You may not specify --instance-type '
+            '\naws: [ERROR]: You may not specify --instance-type '
             'or --instance-count with --instance-groups, '
             'because --instance-type and --instance-count are '
             'shortcut options for --instance-groups.\n'
@@ -800,7 +800,7 @@ def test_instance_groups_exclusive_parameter_validation_error(self):
             '--instance-groups ' + DEFAULT_INSTANCE_GROUPS_ARG
         )
         expect_error_msg = (
-            '\naws: error: You may not specify --instance-type '
+            '\naws: [ERROR]: You may not specify --instance-type '
             'or --instance-count with --instance-groups, '
             'because --instance-type and --instance-count are '
             'shortcut options for --instance-groups.\n'
@@ -938,7 +938,7 @@ def test_ec2_attributes_subnet_az_error(self):
             + 'SubnetId=subnet-123456,AvailabilityZone=us-east-1a'
         )
         expect_error_msg = (
-            '\naws: error: You may not specify both a SubnetId and an Availab'
+            '\naws: [ERROR]: You may not specify both a SubnetId and an Availab'
             'ilityZone (placement) because ec2SubnetId implies a placement.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1004,7 +1004,7 @@ def test_bootstrap_actions_exceed_maximum_error(self):
             cmd += ba_cmd
 
         expected_error_msg = (
-            '\naws: error: maximum number of '
+            '\naws: [ERROR]: maximum number of '
             + 'bootstrap actions for a cluster exceeded.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1021,7 +1021,7 @@ def test_bootstrap_actions_exceed_maximum_with_applications_error(self):
         for i in range(1, 15):
             cmd += ba_cmd
         expected_error_msg = (
-            '\naws: error: maximum number of '
+            '\naws: [ERROR]: maximum number of '
             + 'bootstrap actions for a cluster exceeded.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1194,7 +1194,7 @@ def test_applications_all_types_from_json_file(self):
     def test_wrong_step_type_error(self):
         cmd = DEFAULT_CMD + '--steps Type=unknown'
         expected_error_msg = (
-            '\naws: error: The step type unknown is not supported.\n'
+            '\naws: [ERROR]: The step type unknown is not supported.\n'
         )
         result = self.run_cmd(cmd, 252)
         self.assertEqual(expected_error_msg, result[1])
@@ -1208,7 +1208,7 @@ def test_default_step_type_name_action_on_failure(self):
     def test_custom_jar_step_missing_jar(self):
         cmd = DEFAULT_CMD + '--steps Name=CustomJarMissingJar'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for CustomJARStepConfig: Jar.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1255,7 +1255,7 @@ def test_streaming_step_with_default_fields(self):
     def test_streaming_step_missing_args(self):
         cmd = DEFAULT_CMD + '--steps Type=Streaming'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for StreamingStepConfig: Args.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1288,7 +1288,7 @@ def test_hive_step_with_default_fields(self):
     def test_hive_step_missing_args(self):
         cmd = DEFAULT_CMD + '--applications Name=Hive --steps Type=Hive'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for HiveStepConfig: Args.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1318,7 +1318,7 @@ def test_pig_step_with_default_fields(self):
     def test_pig_missing_args(self):
         cmd = DEFAULT_CMD + '--applications Name=Pig --steps Type=Pig'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for PigStepConfig: Args.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1351,7 +1351,7 @@ def test_impala_step_with_default_fields(self):
     def test_impala_missing_args(self):
         cmd = DEFAULT_CMD + '--applications Name=Impala --steps Type=Impala'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for ImpalaStepConfig: Args.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1412,7 +1412,7 @@ def test_restore_from_hbase(self):
     def test_empty_step_args(self):
         cmd = DEFAULT_CMD + '--steps Type=Streaming,Args= '
         expect_error_msg = (
-            '\naws: error: The prameter Args cannot ' 'be an empty list.\n'
+            '\naws: [ERROR]: The prameter Args cannot ' 'be an empty list.\n'
         )
         result = self.run_cmd(cmd, 252)
         self.assertEqual(expect_error_msg, result[1])
@@ -1427,7 +1427,7 @@ def test_empty_step_args(self):
 
         cmd = DEFAULT_CMD + '--steps Args= '
         expect_error_msg = (
-            '\naws: error: The following required parameters '
+            '\naws: [ERROR]: The following required parameters '
             'are missing for CustomJARStepConfig: Jar.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1451,12 +1451,12 @@ def test_missing_applications_for_steps(self):
         )
 
         expected_error_msg1 = (
-            '\naws: error: Some of the steps require the following'
+            '\naws: [ERROR]: Some of the steps require the following'
             ' applications to be installed: Impala, Pig. '
             'Please install the applications using --applications.\n'
         )
         expected_error_msg2 = (
-            '\naws: error: Some of the steps require the following'
+            '\naws: [ERROR]: Some of the steps require the following'
             ' applications to be installed: Pig, Impala. '
             'Please install the applications using --applications.\n'
         )
@@ -1485,12 +1485,12 @@ def test_missing_applications_with_hbase(self):
         )
 
         expected_error_msg1 = (
-            '\naws: error: Some of the steps require the following'
+            '\naws: [ERROR]: Some of the steps require the following'
             ' applications to be installed: Hbase, Impala. '
             'Please install the applications using --applications.\n'
         )
         expected_error_msg2 = (
-            '\naws: error: Some of the steps require the following'
+            '\naws: [ERROR]: Some of the steps require the following'
             ' applications to be installed: Impala, Hbase. '
             'Please install the applications using --applications.\n'
         )
@@ -1632,7 +1632,7 @@ def test_instance_group_with_autoscaling_policy_missing_autoscaling_role(
             + CONSTANTS.INSTANCE_GROUPS_WITH_AUTOSCALING_POLICY_ARG
         )
         expected_error_msg = (
-            '\naws: error: Must specify --auto-scaling-role when'
+            '\naws: [ERROR]: Must specify --auto-scaling-role when'
             ' configuring an AutoScaling policy for an instance group.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1990,7 +1990,7 @@ def test_instance_fleets_with_both_az_azs_specified(self):
             + ' --ec2-attributes AvailabilityZone=us-east-1a,AvailabilityZones=[us-east-1a,us-east-1b]'
         )
         expected_error_msg = (
-            '\naws: error: You cannot specify both AvailabilityZone'
+            '\naws: [ERROR]: You cannot specify both AvailabilityZone'
             ' and AvailabilityZones options together.\n'
         )
         result = self.run_cmd(cmd, 252)
diff --git a/tests/unit/customizations/emr/test_create_cluster_release_label.py b/tests/unit/customizations/emr/test_create_cluster_release_label.py
index df45de1b04fd..2d987384dfd2 100644
--- a/tests/unit/customizations/emr/test_create_cluster_release_label.py
+++ b/tests/unit/customizations/emr/test_create_cluster_release_label.py
@@ -289,7 +289,7 @@ def test_ami_version_release_label_exclusive_validation(self):
             'emr-4.0.0 --instance-groups ' + DEFAULT_INSTANCE_GROUPS_ARG
         )
         expected_error_msg = (
-            '\naws: error: You cannot specify both --ami-version'
+            '\naws: [ERROR]: You cannot specify both --ami-version'
             ' and --release-label options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -298,7 +298,7 @@ def test_ami_version_release_label_exclusive_validation(self):
     def test_if_ami_version_or_release_label_is_provided(self):
         cmd = self.prefix + ' --instance-groups ' + DEFAULT_INSTANCE_GROUPS_ARG
         expected_error_msg = (
-            '\naws: error: Either --ami-version or'
+            '\naws: [ERROR]: Either --ami-version or'
             ' --release-label is required.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -406,7 +406,7 @@ def test_mutual_exclusive_use_default_roles_and_service_role(self):
             + '--ec2-attributes InstanceProfile=Ec2_InstanceProfile'
         )
         expected_error_msg = (
-            '\naws: error: You cannot specify both --use-default-roles '
+            '\naws: [ERROR]: You cannot specify both --use-default-roles '
             'and --ec2-attributes InstanceProfile options together. Either '
             'choose --use-default-roles or use both --service-role <roleName>'
             ' and --ec2-attributes InstanceProfile=<profileName>.\n'
@@ -420,7 +420,7 @@ def test_mutual_exclusive_use_default_roles_and_instance_profile(self):
             '--ec2-attributes InstanceProfile=Ec2_InstanceProfile'
         )
         expected_error_msg = (
-            '\naws: error: You cannot specify both --use-default-roles '
+            '\naws: [ERROR]: You cannot specify both --use-default-roles '
             'and --service-role options together. Either choose '
             '--use-default-roles or use both --service-role <roleName> '
             'and --ec2-attributes InstanceProfile=<profileName>.\n'
@@ -479,7 +479,7 @@ def test_auto_terminate_and_no_auto_terminate(self):
             + '--auto-terminate --no-auto-terminate'
         )
         expected_error_msg = (
-            '\naws: error: cannot use both --no-auto-terminate and'
+            '\naws: [ERROR]: cannot use both --no-auto-terminate and'
             ' --auto-terminate options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -502,7 +502,7 @@ def test_termination_protected_and_no_termination_protected(self):
             DEFAULT_CMD + '--termination-protected --no-termination-protected'
         )
         expected_error_msg = (
-            '\naws: error: cannot use both --termination-protected'
+            '\naws: [ERROR]: cannot use both --termination-protected'
             ' and --no-termination-protected options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -532,7 +532,7 @@ def test_unhealthy_node_replacement_and_no_unhealthy_node_replacement(
             + '--unhealthy-node-replacement --no-unhealthy-node-replacement'
         )
         expected_error_msg = (
-            '\naws: error: cannot use both --unhealthy-node-replacement'
+            '\naws: [ERROR]: cannot use both --unhealthy-node-replacement'
             ' and --no-unhealthy-node-replacement options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -551,7 +551,7 @@ def test_no_visible_to_all_users(self):
     def test_visible_to_all_users_and_no_visible_to_all_users(self):
         cmd = DEFAULT_CMD + '--visible-to-all-users --no-visible-to-all-users'
         expected_error_msg = (
-            '\naws: error: cannot use both --visible-to-all-users and '
+            '\naws: [ERROR]: cannot use both --visible-to-all-users and '
             '--no-visible-to-all-users options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -572,7 +572,7 @@ def test_no_extended_support(self):
     def test_extended_support_and_no_extended_support(self):
         cmd = DEFAULT_CMD + '--extended-support --no-extended-support'
         expected_error_msg = (
-            '\naws: error: cannot use both --extended-support'
+            '\naws: [ERROR]: cannot use both --extended-support'
             ' and --no-extended-support options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -625,7 +625,7 @@ def test_enable_debugging(self):
     def test_enable_debugging_no_log_uri(self):
         cmd = DEFAULT_CMD + '--enable-debugging'
         expected_error_msg = (
-            '\naws: error: LogUri not specified. You must specify a logUri'
+            '\naws: [ERROR]: LogUri not specified. You must specify a logUri'
             ' if you enable debugging when creating a cluster.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -638,7 +638,7 @@ def test_enable_debugging_and_no_enable_debugging(self):
             + ' --log-uri s3://test/logs'
         )
         expected_error_msg = (
-            '\naws: error: cannot use both --enable-debugging and '
+            '\naws: [ERROR]: cannot use both --enable-debugging and '
             '--no-enable-debugging options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -718,7 +718,7 @@ def test_instance_groups_missing_required_parameter_error(self):
             ' emr-4.0.0 '
         )
         expect_error_msg = (
-            '\naws: error: Must specify either --instance-groups or '
+            '\naws: [ERROR]: Must specify either --instance-groups or '
             '--instance-type with --instance-count(optional) to '
             'configure instance groups.\n'
         )
@@ -730,7 +730,7 @@ def test_instance_groups_missing_required_parameter_error(self):
             '--instance-count 2'
         )
         expect_error_msg = (
-            '\naws: error: Must specify either --instance-groups or '
+            '\naws: [ERROR]: Must specify either --instance-groups or '
             '--instance-type with --instance-count(optional) to '
             'configure instance groups.\n'
         )
@@ -744,7 +744,7 @@ def test_instance_groups_exclusive_parameter_validation_error(self):
             + DEFAULT_INSTANCE_GROUPS_ARG
         )
         expect_error_msg = (
-            '\naws: error: You may not specify --instance-type '
+            '\naws: [ERROR]: You may not specify --instance-type '
             'or --instance-count with --instance-groups, '
             'because --instance-type and --instance-count are '
             'shortcut options for --instance-groups.\n'
@@ -758,7 +758,7 @@ def test_instance_groups_exclusive_parameter_validation_error(self):
             '--instance-groups ' + DEFAULT_INSTANCE_GROUPS_ARG
         )
         expect_error_msg = (
-            '\naws: error: You may not specify --instance-type '
+            '\naws: [ERROR]: You may not specify --instance-type '
             'or --instance-count with --instance-groups, '
             'because --instance-type and --instance-count are '
             'shortcut options for --instance-groups.\n'
@@ -927,7 +927,7 @@ def test_ec2_attributes_subnet_az_error(self):
             + 'SubnetId=subnet-123456,AvailabilityZone=us-east-1a'
         )
         expect_error_msg = (
-            '\naws: error: You may not specify both a SubnetId and an Availab'
+            '\naws: [ERROR]: You may not specify both a SubnetId and an Availab'
             'ilityZone (placement) because ec2SubnetId implies a placement.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -993,7 +993,7 @@ def test_bootstrap_actions_exceed_maximum_error(self):
             cmd += ba_cmd
 
         expected_error_msg = (
-            '\naws: error: maximum number of '
+            '\naws: [ERROR]: maximum number of '
             + 'bootstrap actions for a cluster exceeded.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1006,7 +1006,7 @@ def test_bootstrap_actions_exceed_maximum_with_applications_error(self):
         for i in range(1, 20):
             cmd += ba_cmd
         expected_error_msg = (
-            '\naws: error: maximum number of '
+            '\naws: [ERROR]: maximum number of '
             + 'bootstrap actions for a cluster exceeded.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1057,7 +1057,7 @@ def test_bootstrap_actions_from_json_file(self):
     def test_wrong_step_type_error(self):
         cmd = DEFAULT_CMD + '--steps Type=unknown'
         expected_error_msg = (
-            '\naws: error: The step type unknown is not supported.\n'
+            '\naws: [ERROR]: The step type unknown is not supported.\n'
         )
         result = self.run_cmd(cmd, 252)
         self.assertEqual(expected_error_msg, result[1])
@@ -1071,7 +1071,7 @@ def test_default_step_type_name_action_on_failure(self):
     def test_custom_jar_step_missing_jar(self):
         cmd = DEFAULT_CMD + '--steps Name=CustomJarMissingJar'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for CustomJARStepConfig: Jar.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1118,7 +1118,7 @@ def test_streaming_step_with_default_fields(self):
     def test_streaming_step_missing_args(self):
         cmd = DEFAULT_CMD + '--steps Type=Streaming'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for StreamingStepConfig: Args.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1152,7 +1152,7 @@ def test_hive_step_with_default_fields(self):
     def test_hive_step_missing_args(self):
         cmd = DEFAULT_CMD + '--applications Name=Hive --steps Type=Hive'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for HiveStepConfig: Args.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1183,7 +1183,7 @@ def test_pig_step_with_default_fields(self):
     def test_pig_missing_args(self):
         cmd = DEFAULT_CMD + '--applications Name=Pig --steps Type=Pig'
         expect_error_msg = (
-            '\naws: error: The following '
+            '\naws: [ERROR]: The following '
             + 'required parameters are missing for PigStepConfig: Args.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1331,7 +1331,7 @@ def test_instance_group_with_autoscaling_policy_missing_autoscaling_role(
             + CONSTANTS.INSTANCE_GROUPS_WITH_AUTOSCALING_POLICY_ARG
         )
         expected_error_msg = (
-            '\naws: error: Must specify --auto-scaling-role when'
+            '\naws: [ERROR]: Must specify --auto-scaling-role when'
             ' configuring an AutoScaling policy for an instance group.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1582,7 +1582,7 @@ def test_instance_fleets_with_both_fleet_group_specified(self):
             + CONSTANTS.INSTANCE_GROUPS_WITH_EBS_VOLUME_ARG
         )
         expected_error_msg = (
-            '\naws: error: You cannot specify both --instance-groups'
+            '\naws: [ERROR]: You cannot specify both --instance-groups'
             ' and --instance-fleets options together.\n'
         )
         result = self.run_cmd(cmd, 252)
@@ -1596,7 +1596,7 @@ def test_instance_fleets_with_both_subnetid_subnetids_specified(self):
             + ' --ec2-attributes SubnetId=subnetid-1,SubnetIds=[subnetid-1,subnetid-2]'
         )
         expected_error_msg = (
-            '\naws: error: You cannot specify both SubnetId'
+            '\naws: [ERROR]: You cannot specify both SubnetId'
             ' and SubnetIds options together.\n'
         )
         result = self.run_cmd(cmd, 252)
diff --git a/tests/unit/customizations/emr/test_create_hbase_backup.py b/tests/unit/customizations/emr/test_create_hbase_backup.py
index c1837ddab414..f5bcaa883b1e 100644
--- a/tests/unit/customizations/emr/test_create_hbase_backup.py
+++ b/tests/unit/customizations/emr/test_create_hbase_backup.py
@@ -62,7 +62,7 @@ def test_unsupported_command_on_release_based_cluster_error(
         args = ' --cluster-id j-ABCD --dir s3://abc/'
         cmdline = self.prefix + args
         expected_error_msg = (
-            "\naws: error: create-hbase-backup"
+            "\naws: [ERROR]: create-hbase-backup"
             " is not supported with 'emr-4.0' release.\n"
         )
         result = self.run_cmd(cmdline, 252)
diff --git a/tests/unit/customizations/emr/test_disable_hbase_backup.py b/tests/unit/customizations/emr/test_disable_hbase_backup.py
index 0cd4d27ddbd9..5ecd5a9b3d6f 100644
--- a/tests/unit/customizations/emr/test_disable_hbase_backup.py
+++ b/tests/unit/customizations/emr/test_disable_hbase_backup.py
@@ -73,7 +73,7 @@ def test_disable_hbase_backups_none(self):
         args = ' --cluster-id j-ABCD'
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\nShould specify at least one of --full' + ' and --incremental.\n'
+            '\naws: [ERROR]: Should specify at least one of --full' + ' and --incremental.\n'
         )
         result = self.run_cmd(cmdline, 252)
 
@@ -87,7 +87,7 @@ def test_unsupported_command_on_release_based_cluster_error(
         args = ' --cluster-id j-ABCD --full'
         cmdline = self.prefix + args
         expected_error_msg = (
-            "\naws: error: disable-hbase-backups"
+            "\naws: [ERROR]: disable-hbase-backups"
             " is not supported with 'emr-4.0' release.\n"
         )
         result = self.run_cmd(cmdline, 252)
diff --git a/tests/unit/customizations/emr/test_install_applications.py b/tests/unit/customizations/emr/test_install_applications.py
index 8344b3964ba1..eb623a4f7fb6 100644
--- a/tests/unit/customizations/emr/test_install_applications.py
+++ b/tests/unit/customizations/emr/test_install_applications.py
@@ -120,7 +120,7 @@ def test_install_impala_error(self):
         cmdline = self.prefix + ' Name=Impala'
 
         expected_error_msg = (
-            "\naws: error: Impala cannot be installed on"
+            "\naws: [ERROR]: Impala cannot be installed on"
             + " a running cluster. 'Name' should be one of the following:"
             + " HIVE, PIG\n"
         )
@@ -131,7 +131,7 @@ def test_install_unknown_app_error(self):
         cmdline = self.prefix + 'Name=unknown'
 
         expected_error_msg = (
-            "\naws: error: Unknown application: unknown."
+            "\naws: [ERROR]: Unknown application: unknown."
             + " 'Name' should be one of the following: HIVE, PIG, HBASE,"
             + " GANGLIA, IMPALA, SPARK, MAPR, MAPR_M3, MAPR_M5, MAPR_M7\n"
         )
@@ -149,7 +149,7 @@ def test_unsupported_command_on_release_based_cluster_error(
         )
 
         expected_error_msg = (
-            "\naws: error: install-applications"
+            "\naws: [ERROR]: install-applications"
             " is not supported with 'emr-4.0' release.\n"
         )
         result = self.run_cmd(cmdline, 252)
diff --git a/tests/unit/customizations/emr/test_list_clusters.py b/tests/unit/customizations/emr/test_list_clusters.py
index 2a0eda9ef33c..fc7ab1247a64 100644
--- a/tests/unit/customizations/emr/test_list_clusters.py
+++ b/tests/unit/customizations/emr/test_list_clusters.py
@@ -58,7 +58,7 @@ def test_exclusive_states_filters(self):
         args = '--active --failed'
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\naws: error: You can specify only one of the cluster state '
+            '\naws: [ERROR]: You can specify only one of the cluster state '
             'filters: --cluster-states, --active, --terminated, --failed.\n'
         )
         result = self.run_cmd(cmdline, 252)
@@ -67,7 +67,7 @@ def test_exclusive_states_filters(self):
         args = '--cluster-states STARTING RUNNING --terminated'
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\naws: error: You can specify only one of the cluster state '
+            '\naws: [ERROR]: You can specify only one of the cluster state '
             'filters: --cluster-states, --active, --terminated, --failed.\n'
         )
         result = self.run_cmd(cmdline, 252)
diff --git a/tests/unit/customizations/emr/test_modify_cluster_attributes.py b/tests/unit/customizations/emr/test_modify_cluster_attributes.py
index 71dfd72ed117..98f6b5fe6771 100644
--- a/tests/unit/customizations/emr/test_modify_cluster_attributes.py
+++ b/tests/unit/customizations/emr/test_modify_cluster_attributes.py
@@ -85,7 +85,7 @@ def test_visible_to_all_and_no_visible_to_all(self):
         )
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\naws: error: You cannot specify both --visible-to-all-users '
+            '\naws: [ERROR]: You cannot specify both --visible-to-all-users '
             'and --no-visible-to-all-users options together.\n'
         )
         result = self.run_cmd(cmdline, 252)
@@ -98,7 +98,7 @@ def test_temination_protected_and_no_termination_protected(self):
         )
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\naws: error: You cannot specify both --termination-protected '
+            '\naws: [ERROR]: You cannot specify both --termination-protected '
             'and --no-termination-protected options together.\n'
         )
         result = self.run_cmd(cmdline, 252)
@@ -110,7 +110,7 @@ def test_auto_terminate_and_no_auto_terminate(self):
         )
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\naws: error: You cannot specify both --auto-terminate '
+            '\naws: [ERROR]: You cannot specify both --auto-terminate '
             'and --no-auto-terminate options together.\n'
         )
         result = self.run_cmd(cmdline, 252)
@@ -178,7 +178,7 @@ def test_at_least_one_option(self):
         args = ' --cluster-id j-ABC123456'
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\naws: error: Must specify one of the following boolean options: '
+            '\naws: [ERROR]: Must specify one of the following boolean options: '
             '--visible-to-all-users|--no-visible-to-all-users, '
             '--termination-protected|--no-termination-protected, '
             '--auto-terminate|--no-auto-terminate, '
diff --git a/tests/unit/customizations/emr/test_restore_from_hbase_backup.py b/tests/unit/customizations/emr/test_restore_from_hbase_backup.py
index 2956ad1d963a..feb00ee3b39e 100644
--- a/tests/unit/customizations/emr/test_restore_from_hbase_backup.py
+++ b/tests/unit/customizations/emr/test_restore_from_hbase_backup.py
@@ -63,7 +63,7 @@ def test_unsupported_command_on_release_based_cluster_error(
         args = ' --cluster-id j-ABCD --dir s3://abc/'
         cmdline = self.prefix + args
         expected_error_msg = (
-            "\naws: error: restore-from-hbase-backup"
+            "\naws: [ERROR]: restore-from-hbase-backup"
             " is not supported with 'emr-4.0' release.\n"
         )
         result = self.run_cmd(cmdline, 252)
diff --git a/tests/unit/customizations/emr/test_schedule_hbase_backup.py b/tests/unit/customizations/emr/test_schedule_hbase_backup.py
index 362c19be6f60..636e726ff816 100644
--- a/tests/unit/customizations/emr/test_schedule_hbase_backup.py
+++ b/tests/unit/customizations/emr/test_schedule_hbase_backup.py
@@ -104,7 +104,7 @@ def test_schedule_hbase_backup_wrong_type(self):
         )
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\naws: error: invalid type. type should be'
+            '\naws: [ERROR]: invalid type. type should be'
             + ' either full or incremental.\n'
         )
         result = self.run_cmd(cmdline, 252)
@@ -118,7 +118,7 @@ def test_schedule_hbase_backup_wrong_unit(self):
         )
         cmdline = self.prefix + args
         expected_error_msg = (
-            '\naws: error: invalid unit. unit should be'
+            '\naws: [ERROR]: invalid unit. unit should be'
             + ' one of the following values: minutes,'
             + ' hours or days.\n'
         )
@@ -163,7 +163,7 @@ def test_unsupported_command_on_release_based_cluster_error(
         )
         cmdline = self.prefix + args
         expected_error_msg = (
-            "\naws: error: schedule-hbase-backup"
+            "\naws: [ERROR]: schedule-hbase-backup"
             " is not supported with 'emr-4.0' release.\n"
         )
         result = self.run_cmd(cmdline, 252)
diff --git a/tests/unit/test_clidriver.py b/tests/unit/test_clidriver.py
index e965d6bf352c..3fa7882607c8 100644
--- a/tests/unit/test_clidriver.py
+++ b/tests/unit/test_clidriver.py
@@ -333,7 +333,7 @@ def test_error_unicode(self):
                 rc = self.driver.main('s3 list-objects --bucket foo'.split())
         stderr.flush()
         assert rc == 255
-        assert stderr_b.getvalue().strip() == "☃".encode()
+        assert stderr_b.getvalue().strip() == "aws: [ERROR]: ☃".encode()
 
     @pytest.mark.parametrize(
         'env_vars',
@@ -354,7 +354,7 @@ def test_error_unicode_env_override(self, env_vars):
                 rc = self.driver.main('s3 list-objects --bucket foo'.split())
         stderr.flush()
         assert rc == 255
-        assert stderr_b.getvalue().strip() == "☃".encode()
+        assert stderr_b.getvalue().strip() == "aws: [ERROR]: ☃".encode()
 
     def test_invalid_output_encoding_throws(self):
         stderr_b = io.BytesIO()
@@ -368,7 +368,7 @@ def test_invalid_output_encoding_throws(self):
         fake_stderr.flush()
         assert (
             stderr_b.getvalue().decode().strip()
-            == 'Unknown codec `invalid` specified for AWS_CLI_OUTPUT_ENCODING.'
+            == 'aws: [ERROR]: Unknown codec `invalid` specified for AWS_CLI_OUTPUT_ENCODING.'
         )
 
     def test_can_access_subcommand_table(self):
@@ -725,7 +725,7 @@ def raise_exception(*args, **kwargs):
             driver.main('ec2 describe-instances'.split())
         self.assertEqual(
             f.write.call_args_list[1][0][0],
-            'Unable to locate credentials. '
+            'aws: [ERROR]: Unable to locate credentials. '
             'You can configure credentials by running "aws login".',
         )