new file mode 100644
--- /dev/null
+++ b/testing/config/mozharness/try_arguments.py
@@ -0,0 +1,15 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Because this list exposes new surface to our interface to try, and could
+# easily produce unexpected results if misused, this should only include
+# arguments likely to work with multiple harnesses, and will have unintended
+# effects if conflicts with TryParser are introduced.
+config = {
+    '--tag': {
+        'action': 'append',
+        'dest': 'tags',
+        'default': None,
+    },
+}