katlab tools/regex

Regex · Tester

Test JavaScript regular expressions with live match highlighting, capture groups and flags — all in your browser.

Everything is processed locally. Nothing is uploaded to a server.
/ /

How to test a regex (free)

Type a pattern between the slashes, toggle the flags you need, and paste your text below. Matches are highlighted live and listed with their capture groups. Everything runs locally — nothing is uploaded.

Common regex flags

gglobal — find all matches, not just the first
icase-insensitive
mmultiline — ^ and $ match line starts/ends
sdotall — . also matches newlines
uunicode — full code-point matching
ysticky — match from lastIndex only

Capture groups

Parentheses ( ) create numbered capture groups; (?<name>…) creates a named group. Each match below lists its groups so you can see exactly what the pattern extracts. This is the same ECMAScript engine your JavaScript code uses.

Is my data private?

Yes. Your pattern and test text are evaluated inside your browser tab and never sent anywhere. Because it runs locally, even a slow pattern only affects your own tab — and the tester works offline once loaded.