diff --git a/tools/idf_size.py b/tools/idf_size.py
index 342340002c..80c968239a 100755
--- a/tools/idf_size.py
+++ b/tools/idf_size.py
@@ -1,22 +1,30 @@
 #!/usr/bin/env python
 #
-# SPDX-FileCopyrightText: 2017-2023 Espressif Systems (Shanghai) CO LTD
+# SPDX-FileCopyrightText: 2017-2024 Espressif Systems (Shanghai) CO LTD
 #
 # SPDX-License-Identifier: Apache-2.0
 #
-
 import argparse
 import os
 import subprocess
 import sys
 
 if __name__ == '__main__':
-    parser = argparse.ArgumentParser()
+    # Here the argparse is used only to "peek" into arguments if
+    # legacy version is requested or if old json format is specified.
+    # In these two cases the esp_idf_size legacy version is spawned.
+    parser = argparse.ArgumentParser(exit_on_error=False, add_help=False)
     parser.add_argument('--format')
     parser.add_argument('-l', '--legacy', action='store_true', default=os.environ.get('ESP_IDF_SIZE_LEGACY', '0') == '1')
+
+    # The sys.argv is parsed with "exit_on_error", but the argparse.ArgumentError
+    # exception should never occur, because unknown args should be put into
+    # the rest variable, since the parse_known_args() method is used.
     args, rest = parser.parse_known_args()
 
     if not args.legacy and args.format != 'json':
+        # By default start the refactored version, unless legacy version is explicitly requested with
+        # -l/--legacy option or if old json format is specified.
         try:
             import esp_idf_size.ng  # noqa: F401
         except ImportError:
@@ -24,9 +32,9 @@ if __name__ == '__main__':
             args.legacy = True
         else:
             os.environ['ESP_IDF_SIZE_NG'] = '1'
-
-    if args.legacy and args.format in ['json2', 'raw', 'tree']:
-        sys.exit(f'Legacy esp-idf-size does not support {args.format} format')
+            if not rest or '-h' in rest or '--help' in rest:
+                print(('Note: legacy esp_idf_size version can be invoked by specifying the -l/--legacy '
+                       'option or by setting the ESP_IDF_SIZE_LEGACY environment variable.'))
 
     if args.format is not None:
         rest = ['--format', args.format] + rest