What regex flavor does this use?

JavaScript's built-in RegExp engine (ECMAScript), which supports all standard features: character classes, quantifiers, groups, lookahead/lookbehind, and named capture groups.

What does the 'g' flag do?

The global (g) flag finds all matches instead of stopping at the first one. Without it, only the first match is returned.

How do I use named capture groups?

Use (? pattern) syntax. E.g., /(? \d{4})-(? \d{2})/ captures year and month into named groups accessible as match.groups.year and match.groups.month.

What's the difference between \d and [0-9]?

In most regex engines including JavaScript, \d matches any Unicode decimal digit when the u flag is used, while [0-9] matches only ASCII digits 0–9. For most practical purposes they're equivalent.

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Regex Tester & Debugger

Test regular expressions with real-time match highlighting, capture groups, and replace mode.

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About this tool

Interactive regex testing tool. Enter a pattern and test string to see all matches highlighted in real time. View capture groups, named groups, and match positions. Switch to Replace mode to preview substitutions. Supports all JavaScript regex flags (g, i, m, s, u).

How to use

1 Enter your regular expression in the Pattern field.
2 Optionally add flags (g for all matches, i for case-insensitive, m for multiline).
3 Paste your test string — matches are highlighted in real time.
4 Switch to Replace tab to preview substitutions with $1, $2, or named groups.

Frequently Asked Questions

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