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Regex Tester Online Free — PrivaTools

TL;DR: Paste a regex and a test string and see every match highlighted live, with captured groups. Supports all standard JS flags. Browser-only.

Test regular expressions online for free — paste a regex and a test string to see every match highlighted in real time, along with captured groups. Supports flags (g, i, m, s, u, y). Works entirely in your browser.

Every PrivaTools tool — including Regex Tester — is genuinely free with no premium tier, no per-day limit, and no watermark on the output. Files are deleted from the server within seconds of your download completing. Source code: github.com/taiyeba-dg/privatools.

How to Use Regex Tester

  1. Enter your regex pattern — Type the pattern. JavaScript RegExp syntax (same as in MDN docs).
  2. Set flags — Combine g (global), i (case-insensitive), m (multiline), s (dotall), u (unicode), y (sticky).
  3. Paste test text — Drop the text to match against. Matches highlight in real time as you edit either field.
  4. Read match details — Each match is listed with its offset, captured groups, and matched substring.

Frequently Asked Questions

Which regex flavor does it use?

JavaScript RegExp (ECMAScript). The same engine that powers browser pattern matching. Most patterns are portable to Python re, PCRE, or Go regexp with minor adjustments.

Is my test text saved anywhere?

No. Pattern and text are kept in browser state only. Refresh the page and they're gone. No server-side storage.

How many matches can it handle?

Tested up to ~10,000 matches without slowdown. Beyond that, the highlighting may lag but the match list still renders.

Last reviewed 2026-02-22 by the PrivaTools maintainers. Source code on (MIT-licensed, self-hostable).

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