Regex Tester
Live regex matching with group capture.
Coming soon
Regex Tester is being built and will ship in the next release. It will run 100% in your browser like every other StackPulse utility. The documentation below explains what it does and how it works.
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Open toolWhy test regular expressions?
Regular expressions are the sharpest tool in a developer's kit and the easiest to get wrong. Quantifiers silently greedy, alternations that match the wrong branch, lookaheads with off-by-one boundaries — each of these turns a pattern that 'looks right' into a bug that corrupts data or fails to match a legitimate input. The only reliable way to build a regex is to test it against a representative sample of inputs, and to do that quickly.
A regex tester gives you a live playground: type a pattern and a test string, and matching highlights appear in real time. Capturing groups — the pieces of a match stored for backreferences and extraction — are displayed individually, so you can see exactly which parts of the string each group captured and verify your group numbering before you write it into code.
The tester runs entirely in your browser using the native JavaScript RegExp engine, the same engine your browser and Node.js applications use, so results you see here match what your production code will produce. Pattern flags like i (case-insensitive), g (global) and m (multiline) can be toggled to reproduce real conditions, and your pattern remains safe — never uploaded to any server.
Common use cases
How to test a regular expression
- Type your pattern into the regex field, e.g. \b(https?):\/\/[^\s]+\b.
- Enter a test string, or load one of the built-in samples to see the tool in action.
- Pick the flags you need — g for global, i for case-insensitive, m for multiline, etc.
- Watch the live highlight: matched segments are marked as you type.
- Read the capture group table below the string, then copy the tested pattern into your code.
Test cases
Input · Pattern (\d{4})-\d{2}-\d{2} against "Release on 2026-09-14"
One match on 2026-09-14 with group 1 capturing 2026.
Input · Pattern /a+/ against 'baaab', global flag
A single match 'aaa' highlighted (not three separate 'a' matches).
Frequently asked questions
Is the regex tested with the same engine my code uses?
Yes. Matching runs with the browser's native JavaScript RegExp engine, the same engine used by Node.js and most modern runtimes, so behaviour matches what you will see in production.
How do I read the capture groups?
Every opening parenthesis in your pattern (except non-capturing (?:) creates a group. The tool lists group 0 (the full match) and groups 1..n with the exact captured substrings, letting you verify numbering and matches at a glance.
Is my pattern sent anywhere?
No. The pattern and test string are processed locally — nothing is uploaded, logged or stored by the site.