Regex checker

JavaScript (ECMAScript) regex engine in your browser. Nothing is sent to the server.

What works / what does not
✓ Live match list with index and capture groups✓ Flags g, i, m, s, u, y and /pattern/flags syntax✓ Highlighted matches in the test string✓ Replace preview (optional)✓ Common patterns: email, URL, IPv4, dates✗ PCRE-only features (e.g. (?R), \K)✗ Perl/Python-specific syntax✗ Protection from catastrophic backtracking (max 500 matches)
Presets
Flags
Match found
2 match(es)
Effective: /[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}/g
Matches
#1 at 9
Match: "alice@example.com"
#2 at 30
Match: "bob@test.org"
Highlight
Contact: alice@example.com or bob@test.org for details.