Support: Regex Tester

Tell us what happened. Include which page you were on and what you expected to see. Most answers go out within a business day.

Common questions

Which regex engine does this use?

The one built into your browser, which is the JavaScript engine. Patterns tested here run the same in JavaScript, and almost always in Python, PCRE, Java, .NET and Go too; the cheat sheet notes the few forms that differ.

Why does my pattern match nothing?

Check the flags first: without g only the first match is found, without i case must match exactly, and ^ and $ match only at the ends of the whole text unless m is on. Then check for characters that need escaping, such as a dot or a bracket, and look at the error line under the pattern.

How do I use capture groups?

Wrap part of the pattern in parentheses, (…), and it is listed as $1, $2 and so on under each match. Name a group with (?<name>…) and it is listed by name. In the replacement box, $1 or $<name> inserts what the group matched.

What are the flags?

g finds every match instead of the first; i ignores case; m makes ^ and $ work per line; s lets . match line breaks; u turns on full Unicode so \p{L} and emoji work.

Can I test a replacement?

Yes. Type the replacement text and the result appears below it, with $1, $2, $<name> and $& for the groups and the whole match. Copy result puts it on your clipboard.

Why are there two colours?

Neighbouring matches alternate so you can see where one ends and the next begins, which a single colour hides when matches touch.

Is my text sent anywhere?

No. Everything runs in your browser and nothing is stored.

Is it free?

Yes, completely free, with no sign-up.