Regex Tester

About this regex tester

Type a pattern and it runs against your test string on every keystroke, highlighting each match and capture group in place. Flags, named groups, lookahead and lookbehind are all supported, and the replace preview shows the output before you commit to it.

What most testers do not do is explain the pattern back to you. This one parses it into a syntax tree and renders two things: a plain-English breakdown of what each token matches, and an SVG railroad diagram showing the paths through the expression. A diagram makes an unbalanced alternation or a quantifier attached to the wrong group obvious in a way that reading the source does not.

Patterns you want to keep are saved locally in IndexedDB. Everything runs in your browser: the pattern and the text you test it against are never sent anywhere, which matters when the test data is a real log line or a customer record.