diff --git a/__init__.py b/__init__.py
index 133dca6..02a5d1e 100644
--- a/__init__.py
+++ b/__init__.py
@@ -333,14 +333,14 @@ def parse(
     with_progress=False,
     with_tree=True,
     with_header=False,
-    only_header=False
+    only_header=False,
 ):
     if filename:
         assert not filecontent
         filecontent = builtins.open(filename, encoding=None).read()
         
     if only_header:
-        assert with_header, "'only_header=True' requires 'with_header=True'"
+        with_header = True
 
     # Match and remove the comments
     p = r"/\*[\s\S]*?\*/"
diff --git a/__main__.py b/__main__.py
index 15c98cb..7230888 100644
--- a/__main__.py
+++ b/__main__.py
@@ -1,25 +1,33 @@
 import sys
-import time
+import json
+import argparse
 from . import parse, ValidationError
 
-if __name__ == "__main__":
-    args = [x for x in sys.argv[1:] if not x.startswith("-")]
-    flags = [x for x in sys.argv[1:] if x.startswith("-")]
-
-    fn = args[0]
-    start_time = time.time()
-
+def main():
+    parser = argparse.ArgumentParser(description="Parse and validate STEP file.")
+    parser.add_argument("filename", help="The STEP file to validate.")
+    parser.add_argument("--progress", action="store_true", help="Show progress during validation.")
+    parser.add_argument("--json", action="store_true", help="Output errors in JSON format.")
+    parser.add_argument("--only-header", action="store_true", help="Validate only the header section.")
+    
+    args = parser.parse_args()
+        
     try:
-        parse(filename=fn, with_progress="--progress" in flags, with_tree=False)
-        if "--json" not in flags:
+        parse(
+            filename=args.filename,
+            with_progress = args.progress,
+            with_tree = False,
+            only_header=args.only_header,
+        )
+        if not args.json:
             print("Valid", file=sys.stderr)
         exit(0)
     except ValidationError as exc:
-        if "--json" not in flags:
+        if not args.json:
             print(exc, file=sys.stderr)
         else:
-            import sys
-            import json
-
             json.dump(exc.asdict(), sys.stdout)
         exit(1)
+
+if __name__ == '__main__':
+    main()    
diff --git a/test_parser.py b/test_parser.py
index fb2565a..48f3185 100644
--- a/test_parser.py
+++ b/test_parser.py
@@ -105,4 +105,24 @@ def test_file_mvd_attr():
     assert f.mvd.Remark['SomeKey'] == 'SomeValue'
     assert len(f.mvd.comments) == 2
     assert all(v in vars(f.header).keys() for v in ['file_description', 'file_name', 'file_schema'])
-    assert len(f.header.file_name) == 7
\ No newline at end of file
+    assert len(f.header.file_name) == 7
+
+
+@pytest.mark.parametrize("filename", [
+    'fixtures/fail_invalid_header_entity.ifc',
+    'fixtures/fail_no_header.ifc',
+])
+def test_invalid_headers_(filename):
+    # error in header; with_header should raise an error
+    with pytest.raises(ValidationError):
+        parse(filename=filename, with_tree=False, only_header=True, with_header=True)
+
+@pytest.mark.parametrize("filename", [
+    'fixtures/fail_duplicate_id.ifc',
+    'fixtures/fail_double_comma.ifc',
+    'fixtures/fail_double_semi.ifc'
+])
+def test_valid_headers(filename):
+    # error in body; with_header should not raise an error
+    with nullcontext():
+        parse(filename=filename, with_tree=False, only_header=True, with_header=True)