Why isn't my pattern matching more than once?

Check whether the g (global) flag is on — without it, JavaScript's regex engine stops after the first match, even if more instances exist in the text.

What does the s (dotAll) flag do?

Normally, . (dot) matches any character except a newline. The s flag makes . also match newlines, which is useful when your pattern needs to span multiple lines.

Is my test text or pattern sent anywhere?

No — matching runs entirely in your browser using JavaScript's built-in regex engine; nothing is uploaded or transmitted.

Does it show capture groups separately from the full match?

No — only the full match (equivalent to match[0]) is highlighted; individual capture groups aren't broken out in the results.

What happens with a pattern that can match an empty string, like a*?

It's handled safely — the tool explicitly advances past any zero-width match to avoid an infinite loop, and each zero-width match still counts toward the total shown.

Why does an invalid pattern show a raw JavaScript error message?

It's surfacing the exact error your own code would throw for that pattern — more useful for debugging than a generic message, since it's the real error you'd need to handle either way.

Does the m (multiline) flag change how . (dot) works?

No — m only changes what ^ and $ match, to the start/end of each line instead of the whole string. To make . also match newlines, use the separate s (dotAll) flag.

Can I test more than one pattern against the same text at once?

No — only one pattern and flag combination is active at a time; change the pattern field to try a different one against the same test text.

Regex Tester

About the Regex Tester

Tests a regular expression against sample text, highlighting every match directly in the text, using your browser's native, standards-compliant regex engine.

100% Free Runs in Your Browser No Sign-Up Required

How to use it

Enter a Pattern (without the surrounding slashes).
Toggle the Flags you need — g for all matches, i for case-insensitive, m for multiline anchors, s for dotAll.
Enter or paste your Test text.
Read the match count and see every match highlighted in the text below.

Formula

Uses JavaScript's built-in RegExp engine (ECMA-262) directly — the same regex dialect and matching behavior your pattern would have in actual browser or Node.js code, not a separate simplified implementation.

Worked example

The pattern \b[\w.+-]+@[\w-]+\.[a-zA-Z]{2,}\b with the g and i flags finds every email-like substring in a block of text, highlighting each one in place.

JavaScript regex metacharacter cheat sheet

JavaScript regex metacharacter cheat sheet
Token	Meaning
.	Any character except a line terminator
*	0 or more of the preceding token
+	1 or more of the preceding token
?	0 or 1 of the preceding token (or makes the preceding quantifier lazy)
{n,m}	Between n and m repetitions
\d	Digit (0–9)
\w	Word character (letters, digits, underscore)
\s	Whitespace character
^	Start of string (or line, with the m flag)
$	End of string (or line, with the m flag)
\b	Word boundary
[...]	Character class — any one of the listed characters
(...)	Capture group
\|	Alternation (OR)

Recommendations

• Without the g (global) flag, only the first match is found — turn it on whenever you expect (or want to check for) more than one match.
• The m (multiline) flag changes what ^ and $ mean — they match the start/end of each line instead of the start/end of the whole string, which matters for multi-line test text.
• An invalid pattern (unbalanced parentheses, a bad escape sequence) shows a real JavaScript regex error message — the exact error your own code would throw if you used that pattern directly.

Frequently asked questions

Yes — it runs JavaScript's native RegExp directly in your browser, so a pattern that works here will behave identically in actual JavaScript or Node.js code. Other languages (Python, PCRE, etc.) have their own regex dialects with some differences.

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