Before building Regex Tester, we looked at what the most popular regex testing tool actually asks of you before you can test a pattern.
Seven flavors, one you're probably writing
regex101 supports PCRE2, JavaScript, Python, Go, Java, .NET, Rust, and two POSIX variants — genuinely useful if you work across languages. But if you're testing a pattern for a web form or a Node script, the flavor you need is JavaScript's native RegExp, and picking from a list of seven is a step that doesn't need to exist. This tool only runs JavaScript regex — the same engine your browser and Node already use — so there's no flavor menu at all.
Nothing leaves your browser
Tools that test regex server-side raise a real, if often unstated, tradeoff: your pattern and test text get sent somewhere. Client-side alternatives get called out specifically for avoiding this. This tool matches that bar — everything runs in your browser's own RegExp engine, nothing is transmitted.
Every match, every group
Matches highlight directly in your test text as you type, and each one lists its numbered capture groups ($1, $2...) and any named groups, so you're not squinting at highlighted substrings trying to count parentheses.
