Roblox username rules
Roblox’s support guidance describes a username with 3–20 characters, letters and digits, and at most one underscore. The underscore must be inside the name, rather than first or last.
Source: Roblox Support — Xbox Error 901. Reference checked October 6, 2026.
Formatting and acceptance are separate
Name Lab checks the basic format of its suggestions. Roblox also checks whether a name is already used and whether it passes its moderation rules. This site does not perform those checks, so a generated name is not a promise of availability.
Choose a theme, not personal information
Roblox’s guidance also discourages identifying information in usernames. A favorite animal, setting or fictional theme can provide inspiration without using your full name, address or phone number.
Examples of the format
- MoonOtter: letters only, within the length limit.
- Moon_Otter: one underscore inside the name.
- _MoonOtter: an underscore at the beginning, so it fails the format rule.
- Moon-Otter: a hyphen, which is outside the allowed characters.
These examples explain formatting only; their availability has not been checked.