Regular Expression Tester & Debugger
Test and debug regular expressions with live match highlighting.
Capture Groups
About Regex Tester
Write a regular expression pattern, set flags (g, i, m, s), and test it against any string in real time. Matched segments are highlighted, with individual capture groups shown separately. Great for building and debugging complex patterns without writing test scripts.
Use Cases
Validating email and URL patterns, writing input validation rules, debugging regex in code, extracting data from strings, learning regex syntax interactively.
How It Works
Constructs a JavaScript RegExp object from your pattern and flags, then runs exec() or matchAll() against your test string. Highlights matches using DOM span tags.
FAQs
Which regex flavour is used?
JavaScript (ECMAScript) regex — the same engine used in Node.js, browsers, and most frontend frameworks.
Are look-aheads and named groups supported?
Yes. All ES2018+ features including named capture groups (?<name>...) and look-aheads are supported.
Why are some patterns flagged as invalid?
The tool reports the exact error thrown by the JS RegExp constructor — usually an unescaped special character or unmatched bracket.