What is the difference between . and \S?

. matches any character except newline by default. \S matches any non-whitespace character. Use . with the s (dotAll) flag to match newlines too.

What does \b mean in regex?

\b is a word boundary anchor. It matches the position between a word character (\w) and a non-word character. Use \bword\b to match "word" as a whole word and not as part of "password".

How do I match optional parts of a string?

Use ? after the optional character or group. For example, colou?r matches both "color" and "colour". (\+1 )?\d{10} matches a US phone number with or without the country code.

What is a greedy vs lazy quantifier?

Greedy quantifiers (*, +, {n,m}) match as much as possible. Lazy quantifiers (*?, +?, {n,m}?) match as little as possible. For example, matches the largest possible string between , while matches the smallest.

How do I match a literal dot, bracket, or other special character?

Escape special characters with a backslash. \. matches a literal dot, $ and $ match literal parentheses, \* matches a literal asterisk, and so on.

How do I test if a string matches entirely (full-string match)?

Wrap your pattern with ^ and $: ^yourpattern$. This ensures the entire string must match, not just a substring within it.

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Regex Cheatsheet — Common Patterns and What They Mean

A comprehensive regex cheatsheet for developers at any level. Each section covers a category of common patterns — anchors, character classes, quantifiers, groups, and real-world patterns for email, URL, phone, and date matching — with clear explanations and examples you can test live in the Regex Tester.

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Covers anchors, quantifiers, groups, and character classes

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Real-world patterns with plain-English explanations

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Browse the cheatsheet below, then click any pattern to load it into the Regex Tester and test it against your own data.

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Step-by-step guide to regex cheatsheet — common patterns and what they mean:

1
Anchors: ^ and $
^ matches the start of a string (or line with the m flag). $ matches the end. Use them together — ^pattern$ — to match an entire string rather than a substring.
2
Character classes: [abc] and \d \w \s
[abc] matches any one of a, b, or c. \d matches any digit (0–9). \w matches word characters (letters, digits, underscore). \s matches whitespace. Their uppercase inverses (\D, \W, \S) match the complement.
3
Quantifiers: *, +, ?, {n,m}
* means zero or more. + means one or more. ? means zero or one (optional). {n} means exactly n times. {n,m} means between n and m times. Add ? after any quantifier (e.g. *?) to make it lazy (match as few as possible).
4
Groups: () and (?:)
(abc) captures a group and lets you reference it with \1 or in replace strings. (?:abc) groups without capturing — useful when you need grouping for alternation or quantifiers but do not need the value.
5
Lookahead and lookbehind
(?=...) is a positive lookahead — matches a position followed by the pattern. (?!...) is a negative lookahead. (?<=...) is a positive lookbehind. (?<!...) is a negative lookbehind. These do not consume characters.