How it works
Every keystroke runs your pattern against the text with the JavaScript engine and highlights each match in place. The count sits above the text, and a broken pattern shows the exact syntax error instead of silence.
pattern + flags → highlighted matches
Flag guide
- g: find all matches, not just the first.
- i: ignore upper/lower case.
- m: ^ and $ match each line.
- s: dot matches newlines too.
- u: full Unicode mode (needed for \p{…}).
- y: sticky — match only from the current position.
Tips
- Escape dots in domains: example\.com, not example.com.
- Test with a failing example too — a pattern that matches everything proves nothing.
- Everything runs in your browser; nothing is uploaded.
Standards and sources
- Ecma International — ECMA-262 ECMAScript Language Specification
- TC39 — ECMAScript: RegExp (Regular Expression) Objects
Last reviewed October 13, 2026
Frequently asked questions
Which flavor of regex is this?
JavaScript (ECMAScript) — the same engine websites use, including lookahead and named groups.
Why is my pattern red?
The message under the field quotes the exact syntax error, so fix that spot first.
Is my test text sent anywhere?
No. Matching runs entirely in your browser.
Related tags
#Developer24#Text9#Security11#Color & design9#Work14#Generators & random6#Converters & units5#Time & date8#Students11