Regex Cheat Sheet for Developers: Common Patterns

Regex Fundamentals

Regular expressions (regex) are patterns used to match character combinations in strings. Supported in JavaScript, Python, Go, Java, Ruby, PHP, and virtually every other language.

Core Syntax Quick Reference

Token	Meaning
.	Any character except newline
\d	Digit (0–9)
\w	Word character (a-z, A-Z, 0-9, _)
\s	Whitespace (space, tab, newline)
^	Start of string
$	End of string
*	0 or more
+	1 or more
?	0 or 1 (optional)
{n,m}	Between n and m times
[abc]	Character class (a, b, or c)
[^abc]	Negated class (not a, b, or c)
`(a	b)`
(?:...)	Non-capture group
(?=...)	Positive lookahead

Common Patterns

Email Address

^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$

URL (HTTP/HTTPS)

https?:\/\/(www\.)?[-a-zA-Z0-9@:%._+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_+.~#?&/=]*)

IPv4 Address

^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$

Date (YYYY-MM-DD)

^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])$

Hex Color Code

^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$

UUID v4

^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$

Slug (URL-safe string)

^[a-z0-9]+(?:-[a-z0-9]+)*$

Strong Password

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$

Requires: 1 lowercase, 1 uppercase, 1 digit, 1 special character, min 8 chars.

Practical JavaScript Examples

// Test a pattern
const emailRegex = /^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$/;
console.log(emailRegex.test('user@example.com')); // true

// Extract all matches
const text = 'Call 555-867-5309 or 800-555-1212';
const phones = text.match(/(\d{3}[-.]\d{3}[-.]\d{4})/g);
// ['555-867-5309', '800-555-1212']

// Replace with capture groups
'2026-04-09'.replace(/^(\d{4})-(\d{2})-(\d{2})$/, '$2/$3/$1');
// '04/09/2026'

Flags Reference

Flag	Meaning
g	Global — find all matches
i	Case-insensitive
m	Multiline — ^ and $ match line starts/ends
s	Dotall — . matches newline too

Test Your Regex Online

Use the free Regex Tester on konvertio.app — enter your pattern and test string, see matches highlighted in real time, and understand capture groups at a glance.