See what your pattern really matches
Regular expressions are easy to get almost right. Highlighting every match in the text shows at once whether a pattern is too greedy, misses a case or matches across lines. The groups table lists each match with its position and capture groups, including named groups, so you can check exactly what your code will receive.
The tester uses the JavaScript engine of your browser, so results match Node.js and every modern browser, including Unicode property escapes like \p{L} with the u flag.
No frozen tabs
Some patterns take exponential time on certain inputs, known as catastrophic backtracking. Here the matching runs in a background worker and is stopped after 1.5 seconds with a clear message, so a bad pattern cannot lock up the page. Your text never leaves your device.