How the Bedrock gamertag check works
Minecraft Bedrock does not use Mojang usernames the way Java does. On Bedrock your identity is your Xbox gamertag, because Bedrock accounts sign in through Xbox. That means checking a Bedrock name is really checking an Xbox gamertag, and the rules are Microsoft's, not Mojang's.
This page checks for a public Xbox profile matching the gamertag you enter. If a public profile is found, the tag is almost certainly in use. If no public profile turns up, the name may be free, but that is not a final answer, because some accounts keep their profiles private. For that reason the tool never flatly declares a gamertag available. It shows you the signal, then hands you the exact steps to confirm inside Xbox, which is the only place that can tell you for certain.
Xbox gamertag rules are worth knowing before you settle on one. A unique gamertag can be up to 15 characters. You can use letters, numbers, and single spaces, but a gamertag cannot start with a number and special characters are not allowed. If the base name you want is already taken, Xbox lets you use it anyway and appends a small suffix like #1234 to keep everyone distinct. That suffixed base is capped at 12 characters, and the suffix does not count toward your limit.
To claim or change a gamertag you do it through Xbox, not through Minecraft. On a console, open your profile, go to Customize profile, and choose Change gamertag. In the Xbox app on phone or PC, open your signed in profile and pick the gamertag edit option. Your first gamertag change is typically free, and further changes may carry a small fee. Whatever final tag and suffix Xbox assigns is what shows up in Bedrock.
It helps to remember that Java and Bedrock names are completely separate systems. Owning a Java username does not reserve the matching Bedrock gamertag, and claiming a gamertag has no effect on Java. If you play both editions and want a consistent identity, you have to secure the name in each place on its own. Use this page for the Bedrock side and the main username checker for Java.
A few practical tips for picking a tag Xbox will accept on the first try: keep it within 15 characters, avoid leading numbers and symbols, and have a couple of backups ready in case your first choice returns a public profile. If a tag looks taken here, try a close variation, then run the final candidate through the confirm step in Xbox before you commit.