What does Regex Tester actually do?

The regex tester runs a JavaScript regular expression against text you provide and highlights matches and groups. The flavor is the browser’s, which is the same family Node uses. Lookbehind, unicode sets, and named groups work only when that engine supports them. Patterns are not uploaded.

Which regex flavor does this tester use?

JavaScript (ECMAScript) regex via the browser engine — the same flavor as String.match / RegExp in Node and the browser.

Does my regex leave this device?

No. Patterns and test strings stay in this browser tab.

Is the regex tester free?

Yes — free online regex testing with no account.

Regex Tester

Test JavaScript regular expressions with live match highlighting. Free online — runs locally, no upload.

Pattern

//gi

Test String

Highlighted Matches

Contact: alice@example.com or bob@test.io — also eve@sub.domain.org.

Matches3

#1alice@example.com[alice, example.com]@9

#2bob@test.io[bob, test.io]@30

#3eve@sub.domain[eve, sub.domain]@49

Search tools

Regex Tester