Regex for Username

Validates usernames: starts with a letter, 3-20 characters.

Pattern

/^[a-zA-Z][a-zA-Z0-9_-]{2,19}$/

Live Tester

Enter a string to test

Examples

✓ john_doe

✓ User123

✓ my-name

✗ 1user

✗ ab

✗ user name

Pattern Breakdown

^[a-zA-Z] — must start with a letter

[a-zA-Z0-9_-]{2,19}$ — followed by 2-19 valid characters

Code Snippets

Javascript

const regex = /^[a-zA-Z][a-zA-Z0-9_-]{2,19}$/;
regex.test("john_doe"); // true

Python

import re
pattern = r"^[a-zA-Z][a-zA-Z0-9_-]{2,19}$"
bool(re.match(pattern, "john_doe"))  # True

Php

$pattern = '/^[a-zA-Z][a-zA-Z0-9_-]{2,19}$/';
preg_match($pattern, "john_doe"); // 1

Related Patterns

Email Address /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/ URL /^https?:\/\/(www\.)?[a-zA-Z0-9@:%._+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([a-zA-Z0-9()@:%_+.~#?&/=-]*)$/ Phone Number (International) /^\+?[1-9]\d{1,14}$/ Phone Number (US) /^$?[2-9]\d{2}$?[-.\s]?\d{3}[-.\s]?\d{4}$/ Phone Number (EU) /^\+?[1-9][0-9]{0,3}[\s.-]?$?[0-9]{1,5}$?[\s.-]?[0-9]{1,5}[\s.-]?[0-9]{1,5}$/ IPv4 Address /^((25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(25[0-5]|2[0-4]\d|[01]?\d\d?)$/

Frequently Asked Questions

What is the regex for Username?▾

The regex pattern for Username is /^[a-zA-Z][a-zA-Z0-9_-]{2,19}$/. Validates usernames: starts with a letter, 3-20 characters.

How do I use the Username regex in JavaScript?▾

In JavaScript you create the pattern with a regex literal or the RegExp constructor and call .test() to check a string against it. A ready-to-copy example is shown in the Code Snippets section above, alongside Python and PHP versions.

What does the Username pattern match?▾

It matches strings like john_doe; it rejects strings like 1user. See the Examples section above for the full list of matching and non-matching cases.