Regex Tester
Test a regular expression against sample text and see every match.
Runs entirely in your browser — nothing you paste is sent to our servers.
This is the JavaScript regex flavour, since it uses your browser engine. Most patterns port cleanly, but lookbehind, named groups and Unicode property escapes differ in PCRE, Python and Go — verify before relying on one elsewhere.
What this tool does
Every match, with position
All matches enumerated with their character offset, not just the first.
Capture and named groups
Numbered groups and named groups listed separately, so you can confirm what your code will read.
Live
Re-evaluates on every keystroke in either box, with invalid patterns reported rather than thrown.
Local only
Uses your browser native RegExp engine — your test data is never uploaded.
Frequently asked questions
Which regex flavour is this?
JavaScript (ECMAScript), because it runs in your browser using the native RegExp engine. Most patterns are portable, but lookbehind, named groups and Unicode property escapes differ between languages - verify anything you intend to use in PCRE, Python or Go.
What do the flags mean?
The i flag ignores case, m makes the anchors match line boundaries, s lets the dot match newlines, and u enables full Unicode handling. The global flag is always applied so that every match can be listed.
Why does my pattern only match once?
This tool always enumerates all matches, so if you see one, there is one. If your own code only finds the first, you are probably missing the g flag or using test() rather than matchAll().
What are capture groups?
Parentheses capture the part of the match inside them, numbered from 1. Named groups are listed separately here so you can confirm the name is what your code expects.
Why does it stop at 200 matches?
A safety cap. A pattern that can match the empty string would otherwise produce a match at every position; the result is marked truncated when the cap is hit.
Monitor it, don't just check it
One-off checks catch what is broken today. CertNotify watches your certificates, domains, DNS and code continuously and tells you before something breaks.