How this tester works
The tester uses JavaScript's native RegExp engine, so behavior matches what you'll get in Node.js and browsers. Python, PCRE, and Go dialects are very similar for common patterns but differ on advanced features like lookbehind support and named group syntax.
Quick reference
\d digit · \w word character · \s whitespace · . any character · + one or more · * zero or more · ? optional · ^ start · $ end · [abc] character set · (x) capture group · (?:x) non-capturing group · a{2,4} repetition range.
Privacy
Patterns and test text are processed entirely in your browser and never sent to a server.