Regex Syntax Quick Reference

A comprehensive quick reference for regular expression syntax. Use this alongside our Regex Tester to build and test patterns.

Metacharacters

Character	Description	Example	Matches
`.`	Any character except newline	`a.c`	"abc", "a1c", "a@c"
`\d`	Any digit	`\d{3}`	"123", "456"
`\D`	Any non-digit	`\D+`	"abc", "!@#"
`\w`	Word character (a-z, A-Z, 0-9, _)	`\w+`	"hello", "var_1"
`\W`	Non-word character	`\W`	" ", "@", "!"
`\s`	Whitespace (space, tab, newline)	`\s+`	" ", "\t\n"
`\S`	Non-whitespace	`\S+`	"hello"
`\b`	Word boundary	`\bcat\b`	"cat" in "the cat sat"
`\B`	Non-word boundary	`\Bcat\B`	"cat" in "concatenate"

Character Classes

Pattern	Description	Example	Matches
`[abc]`	Any of a, b, or c	`[aeiou]`	Any vowel
`[^abc]`	Not a, b, or c	`[^0-9]`	Any non-digit
`[a-z]`	Range a to z	`[a-zA-Z]`	Any letter
`[0-9]`	Range 0 to 9	`[0-9]+`	"123", "7"
`[a-zA-Z0-9]`	Alphanumeric	`[a-zA-Z0-9_]+`	"user_123"

Quantifiers

Quantifier	Description	Example	Matches
`*`	0 or more	`ab*c`	"ac", "abc", "abbc"
`+`	1 or more	`ab+c`	"abc", "abbc" (not "ac")
`?`	0 or 1	`colou?r`	"color", "colour"
`{n}`	Exactly n	`\d{4}`	"2024"
`{n,}`	n or more	`\d{2,}`	"12", "123", "1234"
`{n,m}`	Between n and m	`\d{2,4}`	"12", "123", "1234"
`*?`	0 or more (lazy)	`<.*?>`	Shortest match
`+?`	1 or more (lazy)	`".+?"`	Shortest quoted string

Anchors

Anchor	Description	Example	Matches
`^`	Start of string/line	`^Hello`	"Hello" at start
`$`	End of string/line	`end$`	"end" at end
`\A`	Start of string only	`\AStart`	Start of entire string
`\Z`	End of string only	`End\Z`	End of entire string
`\b`	Word boundary	`\bword\b`	Whole word only

Groups and Capturing

Pattern	Description	Example
`(abc)`	Capturing group	`(ha)+` matches "haha"
`(?:abc)`	Non-capturing group	`(?:ha)+` matches but doesn't capture
`(?<name>abc)`	Named group	`(?<year>\d{4})`
`\1`, `\2`	Backreference	`(\w+)\s+\1` matches "the the"
`(?=abc)`	Positive lookahead	`\d(?=px)` matches "5" in "5px"
`(?!abc)`	Negative lookahead	`\d(?!px)` matches "5" not followed by "px"
`(?<=abc)`	Positive lookbehind	`(?<=\$)\d+` matches "50" in "$50"
`(?<!abc)`	Negative lookbehind	`(?<!\$)\d+` matches "50" not after "$"

Flags/Modifiers

Flag	Description
`i`	Case-insensitive matching
`g`	Global (find all matches)
`m`	Multiline (^ and $ match line boundaries)
`s`	Dotall (. matches newlines)
`x`	Verbose (ignore whitespace, allow comments)

Common 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 (US)

^(\+1)?[-.\s]?\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}$

IP Address (IPv4)

^(?:(?: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]\d|3[01])$

Credit Card (basic)

^(?:4[0-9]{12}(?:[0-9]{3})?|5[1-5][0-9]{14}|3[47][0-9]{13})$

Strong Password

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

(Minimum 8 chars, 1 uppercase, 1 lowercase, 1 number, 1 special character)

HTML Tag

<([a-z]+)([^<]+)*(?:>(.*)<\/\1>|\s+\/>)

Hex Color

^#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$

UUID

^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$

Escape Sequences

These characters have special meaning and must be escaped with \ to match literally:

. * + ? ^ $ { } [ ] \ | ( )

Examples:

Match a period: \.
Match a dollar sign: \$
Match a backslash: \\

Language Differences

Feature	JavaScript	Python	C#
Named groups	`(?<name>)`	`(?P<name>)`	`(?<name>)`
Unicode property	`\p{L}` (ES2018+)	`\p{L}` (regex module)	`\p{L}`
Lookbehind	✅ (ES2018+)	✅	✅
Atomic groups	❌	❌	`(?>)`
Possessive quantifiers	❌	❌	`*+`, `++`