Which regex flavour does the tester use?

JavaScript (ECMAScript 2024) by default — including lookbehind, named groups, Unicode property escapes (\p{Letter}) and the v flag. PCRE and Python flavours are also available in the dropdown.

How do I match across multiple lines?

Add the m flag so ^ and $ match line starts/ends, and the s flag so . matches newlines. Both can be on at the same time.

Why is my lookbehind not working?

Lookbehind is supported in modern browsers but not in Safari before 16.4. The tester always works because it runs in your current browser's engine — if your target runtime is older, the warning panel flags it.

Will the regex run on my real text?

Yes — the test box is your real text. Everything runs locally in your browser via the native RegExp engine, so behaviour matches production exactly.

Regex Tester — Free Online Tool

What is the Regex Tester?

The Regex Tester is a free online regex tools from Markvibe. Test regular expressions live with match highlighting. It runs entirely in your browser — your data never gets uploaded — and works on desktop, tablet and mobile with no sign-up.

Reviewed by The Markvibe Team · Last updated 2026-06-28

Example

A worked example so you know exactly what to expect.

Input

Pattern: \b\w+@\w+\.\w+\b
Text: contact us at hello@markvibe.app today

Output

1 match: hello@markvibe.app (positions 16-34)

How to use Regex Tester

1Type your pattern into the regex field, then add flags (g for global, i for case-insensitive, m for multiline, s for dotAll, u for Unicode).
2Paste sample text below — every match is highlighted in real time, with each capture group colour-coded.
3Open the Explain panel to see a plain-English breakdown of every token in your pattern.
4Use the Replace tab to test substitutions, including back-references like $1 and $<name>.
5Copy the final pattern ready to drop into JavaScript, Python, Go or any PCRE-compatible language.

Why use our Regex Tester

✓ 100% free Regex Tester — no sign-up, no watermark, no hidden limits
✓ Runs entirely in your browser so your data never leaves your device
✓ Blazing-fast results — built for speed by Markvibe
✓ Mobile-friendly: use Regex Tester on phone, tablet, or desktop
✓ One of 184+ regex tools utilities under one roof
✓ Privacy-first: no tracking of inputs, no accounts, no ads in the tool area

Regex Tester — frequently asked questions

Regex Explainer

Explain a regex pattern token by token.

See all Regex Tools tools →

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