“All Rights Reserved” is the default state under modern copyright law for any original work — software, writing, images. No one other than the copyright holder may copy, modify, distribute, or create derivative works without explicit permission.
Paradoxically, publishing code on GitHub without a licence makes it “all rights reserved” by default. Viewers can read it, but cannot legally use it. If your goal is for others to use your work, pick an open-source or Creative Commons licence instead.
If your goal is to keep the work private or commercial-only, add a visible copyright notice — and consider writing a proper EULA if you distribute binaries.
How to apply
Add a visible copyright notice to the work:
Copyright (c) 2026 Author Name. All rights reserved.
Pair with a NOTICE file if distributing. For software distributed to end users, a proper EULA is usually required.