Add correct, secure usernames to any Rails model with one line (`has_username`). Format rules that read like English (no symbols at the edges, no two in a row, not all digits), a bundled list of reserved names (admin, root, login, your own routes) matched the way impersonators actually type them (ad.min, adm1n, admin2), offensive-word screening in severity tiers per language, case-insensitive uniqueness that actually uses your index, a free generated name for every account, suggestions when a name is taken, and a live availability check. No table, no network, no API key.