03 / DEVELOPER
Regex Tester
Author and debug JavaScript regular expressions. See matches highlighted live, inspect capture groups, and pick from common ready-made patterns.
How to use
- 1Type or paste your regular expression into the Pattern field — without the surrounding slashes.
- 2Toggle the flags you need (g, i, m, s, u). The g flag is always on so all matches are listed.
- 3Add the text you want to test in the Test string box. Matches are highlighted live and listed in the Matches panel below.
- 4Use Insert sample for a ready-made pattern (email, URL, ISO date, UUID, IPv4) when you just need a quick check.
Frequently asked questions
Which regex flavor is this?
JavaScript's built-in RegExp — exactly what you'd ship in a Node.js or browser project. Patterns that work here will work in your app.
Why did my pattern hang briefly?
We run a watchdog that aborts after about 1.5 seconds or 10,000 iterations to protect against catastrophic backtracking (ReDoS). If you hit it, simplify the pattern or constrain greedy quantifiers.
Are named capture groups supported?
Yes — patterns like `(?<name>...)` work, and matches show the named groups on a second line beneath the positional ones.
Where do the sample patterns come from?
They're hand-written for common debugging scenarios — quick sanity checks rather than RFC-perfect parsers. For production validators, always use a vetted library.