Which regex flavor does this use?

It uses the JavaScript regex engine — the same one that runs in every modern browser. Perl-style features like lookbehind are supported.

Can it explain my regex?

Yes. Click Explain and MyToolsBag returns a plain-English breakdown of every group, quantifier and character class in your pattern.

Is my regex or test string sent anywhere?

Regex execution runs locally. Only the Explain feature calls a language model — the plain regex text is sent to generate the explanation.

How is JavaScript regex different from PCRE, Python, or .NET?

Most day-to-day features work the same. Differences to watch: JavaScript regex has no possessive quantifiers, no atomic groups, no named backreferences in older engines (works in modern browsers), and lookbehind is a newer addition. Patterns copied from PHP or Python usually work; patterns using Perl-only features may not.

What are regex flags and which should I use?

g (global — find all matches instead of just the first), i (ignore case), m (multiline — ^ and $ match per line), s (dotAll — . matches newlines), u (unicode — treat pattern as UTF-16 code points). Use g whenever you want every match, i for case-insensitive text search, and u whenever your input might contain emoji or non-ASCII characters.

How do I match an email address with regex?

A pragmatic pattern is /^[^\s@]+@[^\s@]+\.[^\s@]+$/ — enough for form validation. Do not try to write a full RFC 5322 email regex; it's hundreds of characters and still misses edge cases. For real deliverability, send a verification email.

What's the difference between greedy and lazy quantifiers?

Greedy quantifiers (* + ?) match as much as possible; lazy versions (*? +? ??) match as little as possible. For example, in the string " x ", the pattern matches the whole thing, while matches only . Reach for lazy quantifiers when your match spans further than you expected.

Why does my regex work in the tester but not in my code?

Usually one of three things: your language's regex flavor is different (see above), you forgot to escape the backslashes inside a string literal (\d becomes \\d in a JS string), or you added or removed the g flag and now match/matchAll return different shapes. Copy the pattern out of the tester exactly and re-escape for your language.

MyToolsBag

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Regex Tester & Explainer

Test and debug regular expressions with real-time match highlighting and plain English explanations.

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Contact us at support@mytoolsbag.com or sales@example.com. Visit https://mytoolsbag.com/tools for more information. Call (555) 123-4567 or 555.987.6543. Server IP: 192.168.1.1, deployed on 2024-03-15. ZIP codes: 90210, 10001-1234.

#	Index	Full Match	Capture Groups
1	14	support@mytoolsbag.com	—
2	40	sales@example.com	—