regex tester

How to test a regex online

Regex finds and extracts patterns. Small mistakes cause silent misses or catastrophic backtracking—a live tester saves hours.

Pattern, flags, and text

Enter pattern, flags (g,i,m,s,u), and test text. LedaTools lists matches with indexes and groups using the browser RegExp.

Escape literals. Prefer non-greedy quantifiers when needed. For emails/URLs, consider dedicated parsers.

Matching is local—useful with production-like data.

Ambiguous patterns on hostile input can hang the thread. Avoid (a+)+ on untrusted text in prod.

i = ignore case, m = multiline ^$, s = dotAll, u = unicode. g lists all matches.

Which engine?

The browser’s JavaScript RegExp engine.

Flags?

Yes: g, i, m, s, u, and more.

Is text uploaded?

No. Matching is local.