diff --git a/tests/test_main.py b/tests/test_main.py
new file mode 100644
index 0000000000..484de6ab70
--- /dev/null
+++ b/tests/test_main.py
@@ -0,0 +1,60 @@
+import argparse
+import unittest
+
+from src.main import build_parser
+
+
+class TestMainParser(unittest.TestCase):
+    def setUp(self) -> None:
+        self.parser = build_parser()
+
+    def test_build_parser_returns_argument_parser(self) -> None:
+        self.assertIsInstance(self.parser, argparse.ArgumentParser)
+        self.assertEqual(
+            self.parser.description,
+            "Python porting workspace for the Claude Code rewrite effort",
+        )
+
+    def test_parser_has_expected_commands(self) -> None:
+        # Check a few simple commands that require no extra arguments
+        args = self.parser.parse_args(["summary"])
+        self.assertEqual(args.command, "summary")
+
+        args = self.parser.parse_args(["manifest"])
+        self.assertEqual(args.command, "manifest")
+
+        args = self.parser.parse_args(["tool-pool"])
+        self.assertEqual(args.command, "tool-pool")
+
+    def test_parser_commands_with_arguments(self) -> None:
+        # Check a command with default arguments
+        args = self.parser.parse_args(["subsystems"])
+        self.assertEqual(args.command, "subsystems")
+        self.assertEqual(args.limit, 32)
+
+        # Check overriding default arguments
+        args = self.parser.parse_args(["subsystems", "--limit", "10"])
+        self.assertEqual(args.command, "subsystems")
+        self.assertEqual(args.limit, 10)
+
+        # Check command requiring positional arguments
+        args = self.parser.parse_args(["route", "test prompt", "--limit", "2"])
+        self.assertEqual(args.command, "route")
+        self.assertEqual(args.prompt, "test prompt")
+        self.assertEqual(args.limit, 2)
+
+    def test_parser_invalid_command(self) -> None:
+        # argparse uses sys.exit(2) for invalid arguments
+        with self.assertRaises(SystemExit) as cm:
+            self.parser.parse_args(["this-command-does-not-exist"])
+        self.assertEqual(cm.exception.code, 2)
+
+    def test_parser_missing_required_command(self) -> None:
+        # argparse uses sys.exit(2) when a required subcommand is missing
+        with self.assertRaises(SystemExit) as cm:
+            self.parser.parse_args([])
+        self.assertEqual(cm.exception.code, 2)
+
+
+if __name__ == "__main__":
+    unittest.main()