Which regex engine does the tester use?

It uses the browser's native JavaScript ECMAScript RegExp engine, so matching behavior corresponds to JavaScript and Node.js.

Can a pathological pattern freeze the page?

Matching runs in a worker with a timeout. A timeout stops the operation and reports a likely catastrophic-backtracking case.

What can I inspect in a match?

The result highlights matches in the test string and reports capture groups, named groups and positions.

Regex Tester

Test JavaScript regular expressions with live match highlighting, capture groups, substitution, and shareable links.

About this tool

Regex Tester runs entirely in your browser on DevTools — no signup, no upload.

What this tool does not do

Regex Tester is a free in-browser utility, not a hosted API, and keeps no server-side history.

How to use this tool

Using Regex Tester
Open Regex Tester, enter or paste your input, and copy the result.

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