Regex Tester
Enter a pattern (without slashes), flags such as g, i, m or u, and test text, then press Test. Each match is listed with its position and capture groups. Patterns run in a worker with a time limit, so catastrophic backtracking is stopped instead of freezing the page.
This tool runs in an isolated frame on tools.freetoolspro.com. Your files and inputs stay on your device, and advertising on this page cannot read them.
Engine
Your browser’s JavaScript RegExp engine is used, so behaviour matches code running in the same browser. The g flag is added automatically to list all matches; the first 1,000 are shown.
Privacy
Your text is processed by a Web Worker inside the isolated tools.freetoolspro.com frame. It is not uploaded, logged or shown to advertising scripts on this page, and it is gone when you close the tab.
Common questions
Does it support lookbehind?
Yes in all current browsers.
Why was my pattern stopped?
It took over four seconds, usually because nested quantifiers cause exponential backtracking.
Methodology reviewed 2026-10-27. Processing details and test approach.