Regular expressions are famously easy to get almost right: a pattern that matches your first example quietly fails on the edge case that reaches production. This tester shows you what a pattern does while you type it. Enter a JavaScript regular expression with any of the g, i, m, s, u and y flags, and every match in the test text highlights live, so a misplaced quantifier or greedy wildcard is visible immediately.
Below the editor, a table lists each match with its index in the text and every capture group it produced, both numbered and named. So you can confirm a log-parsing pattern captures the timestamp into the right group, or an extraction regex splits a URL correctly, before it goes anywhere near your codebase.
Both your pattern and your test text stay on your machine from the first keystroke. Matching runs on your browser's own regex engine, so nothing is sent to a server, and the log lines, emails or source snippets you test against are never visible to anyone else.
Not exactly. It uses the JavaScript regex engine, which differs from PCRE and Python in places: there is no free-spacing x flag, and Python spells named groups differently. A pattern that works here will work in JavaScript, but retest in the target language before using it elsewhere.
Write them as (?<name>pattern), for example (?<year>\d{4})-(?<month>\d{2}) to pull apart a date. The match table shows each named group with its label, and in JavaScript code the same values appear under match.groups.year.
You probably have not enabled the g flag. Without it, a JavaScript regex stops after the first match it finds. Turn on g to find every occurrence; the highlights and the match table will update to show all of them.