Pattern
/^[A-Za-z][A-Za-z0-9_]{2,15}$/Sample text
alice_01 _bad ab toolongusername12345Test this pattern in the editor
Usernames
3–16 chars: letter start, then letters, digits, underscore.
Related patterns
Email addresses
Capture local and domain parts from common email shapes.
HTTP(S) URLs
Match protocol, host, and optional path/query.
Strong-ish password
Require length and mixed character classes (demo only).
E.164 phone numbers
International numbers with leading + and country code.
Russian phone numbers
Common +7 / 8 mobile formats with optional separators.
US phone numbers
North American formats with optional country code.