What regex syntax is supported?

This tool uses JavaScript's native RegExp engine, which supports most modern regex features including lookahead (?=), lookbehind (? ), and Unicode properties.

What do the flags mean?

g (global) finds all matches, i (case-insensitive) ignores case, m (multiline) makes ^ and $ match line boundaries, s (dotAll) makes . match newlines.

Why is my regex slow?

Regex can be slow with catastrophic backtracking. Avoid nested quantifiers like (a+)+ and use atomic groups or possessive quantifiers when possible.

// regex-tester

Regex Tester

Test regular expressions with real-time matching, highlighting, and match details.

Global (g)Case Insensitive (i)Multiline (m)DotAll (s)

Test String

Matches0

How to Use Regex Tester

Enter pattern-Type a regular expression pattern in the pattern field.
Set flags-Toggle regex flags like global (g), case-insensitive (i), or multiline (m).
Enter test string-Type or paste the text you want to test the pattern against.
View matches-Matches are highlighted in the test string and listed with capture group details.

About Regex Tester

Regex Tester lets you build and test regular expressions in real time. Matches are highlighted in the test string and detailed match information is displayed.

It supports all JavaScript regex features including capture groups, lookaheads, lookbehinds, and named groups.

All processing happens in your browser using the native JavaScript RegExp engine.

FAQ

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