This is a simple, useful tool to see which usernames have been taken or are available to be owned on GitHub: https://replit.com/@SnakeByte/GitHub-Username-Checker?v=1
It is made using HTML, and it works by utilising a GitHub API (‘api.github.com’) that returns information about a specific GitHub user. If the user exists, information about the requested user is returned. However, if the user is not found, the server responds with a ‘404’ status.