Regex Tester & Explainer

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Write, test, validate, and preview JavaScript regular expressions in real-time.

Regex Tester & Explainer

Test String

Match Highlight0 matches

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Search & Replace

Replace With

Replacement Result

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Capture Groups & Match Details

No matches found to list details.

Presets & Templates

Quick Syntax Guide

.

Any character except newline

\d

Any digit (0-9)

\D

Any non-digit character

\w

Any word character (a-z, A-Z, 0-9, _)

\W

Any non-word character

\s

Any whitespace (spaces, tabs, newlines)

\S

Any non-whitespace character

^

Start of string/line

$

End of string/line

\b

Word boundary

*

0 or more occurrences

+

1 or more occurrences

?

0 or 1 occurrence

{n}

Exactly n occurrences

{n,m}

Between n and m occurrences

[abc]

Any character in the set (a, b, or c)

[^abc]

Any character NOT in the set

(abc)

Capture group (matches abc together)

a|b

Alternation (matches a or b)

Learn to Test and Debug Regular Expressions

A **regular expression** (abbreviated as regex or regexp) is a sequence of characters that specifies a search pattern in text. Usually, such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation.

Understanding Common Regex Flags

Flags modify the behavior of string-matching operations. You can toggle them in our interactive client:

Global (g)

Finds all matches rather than stopping after the first match.

Case-Insensitive (i)

Ignores difference between lowercase and uppercase characters (e.g. [A-Z] matches [a-z]).

Multiline (m)

Allows anchors ^ and $ to match start and end of individual lines rather than the whole string.

Dot All (s)

Forces the dot (.) special character to match newline characters as well.

Frequently Asked Questions

What is a regular expression (regex)?

A regular expression is a syntax structure defining search patterns. It is widely used in text editors, command lines, and programming languages for pattern matching, validation, and replacements.

What does the global flag 'g' do in regex?

The global flag 'g' instructs the regex engine to look for all possible matches throughout the entire text, instead of terminating the search and returning only the first match.

How can I match case-insensitive strings?

By adding the 'i' flag to your regular expression. For example, the pattern '/apple/i' will match 'Apple', 'APPLE', or 'aPpLe'.

What are capturing groups in regular expressions?

Capturing groups are defined using parentheses '()'. They allow you to extract a sub-portion of the matched text or perform structured search-and-replace using backreferences (like $1, $2, etc.).

Is this Regex Tester secure? Does my test text get sent to a server?

Yes, it is 100% secure. This Regex Tester runs entirely in your local browser using client-side JavaScript. None of your test text or pattern definitions are uploaded to a remote server, ensuring full privacy.