A browser-based regex tester is a free alternative to online regex tools that runs your pattern against your test text entirely on your own device, so neither the pattern nor the sample data is transmitted. It highlights matches live and needs no account.
When you build a regular expression you usually test it against real sample data, and that sample is frequently sensitive: log lines with ids, a list of emails, a chunk of a private document. A client-side tester runs the pattern against your text using the browser's own regex engine, so both the pattern and the data you are matching stay on your device.
A good tester highlights the matches as you type and shows the captured groups, which is how you actually refine a pattern. Doing that locally means the feedback is instant and nothing about your regex or your test data is sent anywhere, and it keeps working offline once the page has loaded.
No. The regex runs in your browser, so nothing you type is transmitted.
Yes. Matches are highlighted and captured groups are shown as you edit the pattern.
Yes. Once loaded, testing works with no network connection.