Is this regex tester free?

Yes, completely free — no account, no subscription, no usage limits.

Does it upload my pattern or text to a server?

No. Everything runs locally in your browser using the JavaScript RegExp engine. Nothing is ever sent to any server.

Does it work offline?

Yes. Once the page is loaded, you can disconnect from the internet and it continues to work. The tool is also a PWA, so you can install it for offline use.

Which regex flags are supported?

The tool supports g (global), i (case-insensitive), m (multiline), s (dotAll), and u (unicode) — all standard JavaScript RegExp flags.

Can I use capture groups in the replacement string?

Yes. Use $1, $2, … in the replacement field to reference capture groups from your pattern — just like JavaScript's String.replace().

Why does my pattern behave differently here than in Python or PCRE?

This tester runs the browser's own JavaScript regex engine, which differs from Python and PCRE in real ways: named groups use a different syntax, there is no verbose mode with inline comments, and lookbehind support depends on the browser. If you are writing a pattern for a JavaScript project this is exactly the right engine; for other languages, treat it as close but not identical.

My browser freezes on a long input - what happened?

That is almost certainly catastrophic backtracking. Patterns with nested quantifiers such as (a+)+ can take exponentially longer as the input grows, so a string that is only slightly longer can hang the engine. It is a property of the pattern rather than the tester - and finding it here, on a page you can simply reload, is much better than finding it in production.

🔎 Regex Tester — Live Match, Groups & Replace

Toolio's Regex Tester is a free, browser-only tool that tests regular expressions instantly — no file uploads, no account required, and fully usable offline. Looking for a free regex101 alternative? Toolio’s version is completely free and needs no sign-up.

A regular expression (regex) is a pattern for searching and matching text; a regex tester shows what a pattern matches against sample input.

Regex Pattern

Pattern

Test String

Capture Groups (first match)

Replace

Replacement string ($1, $2 … supported)

Replace preview

Private by design. This tool runs entirely in your browser — nothing you enter is uploaded or stored, and it works offline.

About

Enter a regex pattern and a test string to see every match highlighted in real time. Capture groups from the first match are listed with their $1, $2 … references, and the replace preview shows how your substitution string transforms the input. Flags — g, i, m, s, u — are toggled with checkboxes so you never have to remember the syntax. Because everything runs in your browser with no server involved, your patterns and text stay completely private.

How to use

Type your regular expression into the Pattern field.
Check the flags you need (g for global, i for case-insensitive, m for multiline, etc.).
Paste or type your test string in the Test String area — matches highlight immediately.
Check the Capture Groups panel to inspect $1, $2 … values from the first match.
Enter a replacement string in the Replace field to preview the result, then copy it.

FAQ

Is this regex tester free?: Yes, completely free — no account, no subscription, no usage limits.
Does it upload my pattern or text to a server?: No. Everything runs locally in your browser using the JavaScript RegExp engine. Nothing is ever sent to any server.
Does it work offline?: Yes. Once the page is loaded, you can disconnect from the internet and it continues to work. The tool is also a PWA, so you can install it for offline use.
Which regex flags are supported?: The tool supports g (global), i (case-insensitive), m (multiline), s (dotAll), and u (unicode) — all standard JavaScript RegExp flags.
Can I use capture groups in the replacement string?: Yes. Use $1, $2, … in the replacement field to reference capture groups from your pattern — just like JavaScript's String.replace().
Why does my pattern behave differently here than in Python or PCRE?: This tester runs the browser's own JavaScript regex engine, which differs from Python and PCRE in real ways: named groups use a different syntax, there is no verbose mode with inline comments, and lookbehind support depends on the browser. If you are writing a pattern for a JavaScript project this is exactly the right engine; for other languages, treat it as close but not identical.
My browser freezes on a long input - what happened?: That is almost certainly catastrophic backtracking. Patterns with nested quantifiers such as (a+)+ can take exponentially longer as the input grows, so a string that is only slightly longer can hang the engine. It is a property of the pattern rather than the tester - and finding it here, on a page you can simply reload, is much better than finding it in production.