Username policies affect user experience, security, and platform identity. Well-designed rules prevent abuse while remaining user-friendly.
Username Length and Character Rules
Minimum length (3-4 characters) prevents single-letter squatting while keeping options open. Maximum length (15-30 characters) prevents abuse and display issues. Allow letters, numbers, underscores, and hyphens. Disallow spaces (they complicate @mentions) and special characters that break URLs or databases. Case-insensitive matching (treat User and user as same) prevents confusion and impersonation.
Reserved and Protected Usernames
Reserve system usernames: admin, moderator, support, staff, official. Protect brand names: your company name, competitor names (to prevent phishing). Block common typos of reserved names (adm1n, supp0rt). Create an allowlist for legitimate uses and a blocklist for always-prohibited names. Review and update lists quarterly as your platform grows.
Uniqueness and Display Names
Enforce unique usernames to prevent impersonation. Optionally allow non-unique display names for flexibility. Example: username "john.doe.1985" (unique, immutable) but display name "John Doe" (can be changed, not unique). This separates identity (username) from presentation (display name) and improves user experience.