🔍Regex Recipes

Username (Safe)

Safe username validation with letters, numbers, dots, underscores, and hyphens with length rules.

Pattern

^[a-zA-Z0-9._-]{3,20}$

Explanation

Allows alphanumeric characters plus dots, underscores, and hyphens. Length 3-20 characters.

Examples

Valid

Input

john_doe

Output

✓ Match

Valid

Input

user.name

Output

✓ Match

Valid

Input

user-123

Output

✓ Match

Invalid - too short

Input

ab

Output

✗ No match

Invalid - special char

Input

user@name

Output

✗ No match

Code Examples

JavaScript

const usernameRegex = /^[a-zA-Z0-9._-]{3,20}$/;

function validateUsername(username) {
  if (!usernameRegex.test(username)) {
    return 'Username must be 3-20 characters, letters, numbers, dots, underscores, hyphens only';
  }
  // Additional checks
  if (username.startsWith('.') || username.endsWith('.')) {
    return 'Username cannot start or end with a dot';
  }
  return null; // valid
}

Try it Now

Open in Regex Tester

💡 Tips

Add case-insensitive check for duplicates
Consider blocking profanity and reserved words
Display requirements clearly to users
Allow users to change usernames later

⚠️ Common Pitfalls

Does not prevent consecutive dots or special chars
May want to disallow starting/ending with special chars
Consider reserved usernames (admin, root, etc.)
Length limits should match your database constraints