Regex Tester

Writing a regular expression is a loop of guessing and checking, and this shortens the loop by running your pattern against sample text as you type, highlighting each match. Because it uses the browser's own regular expression engine, what matches here is what will match in your JavaScript — there is no dialect gap between the sandbox and the code. It suits validating an input format, pulling fields out of log lines, or working out why a pattern that looked right catches one case too many. Two things to keep in mind. This is JavaScript regex syntax, and PCRE, Python and .NET differ in places, particularly around lookbehind and named groups. And deeply nested quantifiers on long input can backtrack catastrophically and hang the tab; if typing a pattern freezes the page, that behaviour, not a crash, is usually the explanation.