Roblox username rules explained

The written rules are short. The unwritten ones are what get names rejected. Here's the full picture.

The official rules

• Length: 3 to 20 characters.
• Characters: letters, numbers, and underscores. Nothing else, no spaces.
• Edges: a username cannot start or end with an underscore.
• Case: usernames are unique case-insensitively. Frost and frost are the same name, so registering one blocks the other.
• Moderation: names cannot be inappropriate. This is checked when you register.

The rules nobody tells you

• The moderation filter is aggressive. It catches far more than swear words, including some innocent-looking combinations. A name can pass your eyes and still get rejected at sign-up. That's why a real checker should tell you inappropriate as its own result, not just available or taken.
• Uniqueness is checked against current usernames only. If a name is held by a deleted account, it may or may not be claimable depending on whether Roblox has released it. Checkers can only tell you what the sign-up API says right now.
• Display names are not usernames. Your display name can be almost anything and changed freely. Your username is permanent until you pay for a change. Spend your effort on the username.
• Leading digits read as bots. Names like 88Frost are allowed but look auto-generated. Digit-suffix names (Frost88) read better.
• Underscores in the middle are fine (frost_kite), but each underscore makes a name slightly harder to say and type.

How the checker applies these rules

The tool on this site validates against the same endpoint Roblox's own sign-up form uses. It returns three verdicts:

• Code 0: the name passed every rule and is free right now. Shown as Available.
• Code 1: someone holds the name. Shown as Taken, with the holder's profile, account age and previous usernames.
• Code 2: the name is blocked by moderation. Shown as Inappropriate. Nobody holds it, but you can't register it either.

A name is only ever shown as available when that validation endpoint explicitly accepted it. Names that couldn't be verified are kept in their own tab with a re-check option, because a guess is worse than an honest "don't know".

Quick pre-flight checklist

1. 3 to 20 characters?
2. Only letters, numbers, underscores?
3. No underscore at the start or end?
4. Would a teacher frown at it? Then the filter will too.

Check usernames against the real rules

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