Regex Tester
Test JavaScript regular expressions against your text with live match highlighting, capture groups and a replace preview. A safety timeout stops runaway patterns.
This tool runs entirely in your browser.
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How to use the Regex Tester
- 1Enter a pattern and choose flags (g, i, m, s, u).
- 2Type or paste the test text — matches are highlighted as you type.
- 3Inspect capture groups, or enter a replacement to preview the result.
What is the Regex Tester?
The tester uses your browser’s JavaScript regex engine, so behaviour matches Node.js and browsers exactly. Matching runs in a background worker with a timeout, so catastrophic backtracking cannot freeze the page.
Frequently asked questions
Does it support lookbehind and named groups?
Yes — all modern JavaScript features including (?<name>…), lookbehind (?<=…) and the s (dotAll) and u (Unicode) flags.
Is the Regex Tester free and private?
Yes. The Regex Tester is free, needs no account, and runs entirely in your browser. What you type is never sent to a server or stored.
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