Regex Tools

Regex Cheat Sheet & Reference

Complete regular expressions syntax reference with categorized patterns, quantifiers, lookaround assertions, and practical examples.

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Common Patterns

/^[^\s@]+@[^\s@]+\.[^\s@]+$/

Example: [email protected]

Basic email validation

URL

/https?:\/\/[^\s]+/

Example: https://example.com/path

Match HTTP/HTTPS URLs

IPv4 Address

/\b(?:\d{1,3}\.){3}\d{1,3}\b/

Example: 192.168.1.1

IPv4 address pattern

Chinese Phone

/^1[3-9]\d{9}$/

Example: 13812345678

Mainland China mobile number

Date (YYYY-MM-DD)

/\d{4}-\d{2}-\d{2}/

Example: 2024-01-15

ISO date format

Character Classes

Pattern	Name	Example	Description
`.`	Any character	a.c → abc, aXc	Matches any single character except newline
`\d`	Digit	\d+ → 123	Matches any digit (0-9)
`\D`	Non-digit	\D+ → abc	Matches any non-digit character
`\w`	Word character	\w+ → hello_1	Matches letters, digits, underscore
`\W`	Non-word character	\W+ → !@#	Matches non-word characters
`\s`	Whitespace	a\sb → a b	Matches space, tab, newline
`\S`	Non-whitespace	\S+ → hello	Matches any non-whitespace character
`[abc]`	Character set	[aeiou] → a, e, i	Matches any character in set
`[^abc]`	Negated set	[^0-9] → a, b	Matches any character not in set
`[a-z]`	Character range	[a-z]+ → hello	Matches any character in range

Quantifiers

Pattern	Name	Example	Description
`*`	Zero or more	ab*c → ac, abc, abbc	Matches 0 or more of preceding
`+`	One or more	ab+c → abc, abbc	Matches 1 or more of preceding
`?`	Zero or one	ab?c → ac, abc	Matches 0 or 1 of preceding
`{n}`	Exact count	a{3} → aaa	Matches exactly n occurrences
`{n,}`	n or more	a{2,} → aa, aaa	Matches n or more occurrences
`{n,m}`	Between n and m	a{2,4} → aa, aaa, aaaa	Matches between n and m occurrences
`*?`	Lazy zero or more	a.*?b → ab	Non-greedy matching
`+?`	Lazy one or more	a.+?b → ab	Non-greedy matching

Anchors

Pattern	Name	Example	Description
`^`	Start of string	^hello → hello world	Matches at start of string/line
`$`	End of string	world$ → hello world	Matches at end of string/line
`\b`	Word boundary	\bword\b → the word	Matches word boundary
`\B`	Non-word boundary	\Bword → sword	Matches non-word boundary
`(?=...)`	Positive lookahead	a(?=b) → ab	Matches if followed by pattern
`(?!...)`	Negative lookahead	a(?!b) → ac	Matches if not followed by pattern
`(?<=...)`	Positive lookbehind	(?<=a)b → ab	Matches if preceded by pattern
`(?<!...)`	Negative lookbehind	(?<!a)b → cb	Matches if not preceded by pattern

Groups

Pattern	Name	Example	Description
`(...)`	Capturing group	(ab)+ → abab	Captures matched text
`(?:...)`	Non-capturing group	(?:ab)+ → abab	Groups without capturing
`(?<name>...)`	Named group	(?<year>\d{4})	Captures with name
`\1`	Backreference	(\w)\1 → aa, bb	Matches captured group again
`a\|b`	Alternation	cat\|dog → cat, dog	Matches either expression

Assertions

Pattern	Name	Example	Description
`(?=...)`	Positive lookahead	\d(?=px) → 10px	Assert pattern follows
`(?!...)`	Negative lookahead	\d(?!px) → 10em	Assert pattern does not follow
`(?<=...)`	Positive lookbehind	(?<=\$)\d+ → $100	Assert pattern precedes
`(?<!...)`	Negative lookbehind	(?<!\$)\d+ → €100	Assert pattern does not precede

Flags

Pattern	Name	Example	Description
`g`	Global	/a/g → a, a, a	Find all matches, not just first
`i`	Case insensitive	/abc/i → ABC, abc	Ignore case in matching
`m`	Multiline	/^a/m → ... a	^ and $ match line boundaries
`s`	DotAll / Singleline	/a.*b/s → a b	. matches newlines too
`u`	Unicode	/\u{1F600}/u	Enable Unicode support

What is Regex Cheat Sheet & Reference?

Regex Cheat Sheet & Reference is a comprehensive quick-reference guide for regular expression syntax covering JavaScript PCRE compatible patterns anchors quantifiers character classes groups backreferences and lookaround assertions. Regular expressions are a power tool for text processing but their dense syntax is notoriously difficult to memorize even experienced developers regularly look up the difference between greedy and lazy quantifiers the exact syntax for positive lookaheads or which character classes need escaping inside brackets. This cheat sheet organizes syntax into logically grouped sections Characters Literals Character Classes Shorthands Anchors Boundaries Quantifiers Greedy Lazy Possessive Groups Backreferences Lookahead Lookbehind Assertions Flags Modifiers Substitution Patterns and Common Recipes. Each entry includes pattern syntax plain-English explanation and a testable working example. The Common Recipes section provides production-ready patterns for the forty plus most frequent regex tasks email validation IPv4 IPv6 addresses phone numbers URLs dates credit card numbers password complexity HTML tag extraction and more. Pattern entries include copy buttons and direct links to the Regex Tester for immediate experimentation.

When to Use Regex Cheat Sheet & Reference

Use when building regex patterns for form validation, looking up lookaround syntax, finding pre-built regex recipes for common tasks, memorizing quantifier behavior, or teaching regex concepts to teammates.

How to Use Regex Cheat Sheet & Reference

Browse categorized syntax sections or search for a specific concept. Each entry shows syntax, explanation, and a working example. Click Test to jump directly to the Regex Tester with the pattern pre-loaded.