Regex Tester

Debugging a regex like ^(?:[a-z0-9]+(?:\.[a-z0-9]+)*)@(?:[a-z0-9-]+\.)+[a-z]{2,}$ in your head is painful. The Regex Tester gives you real-time match highlighting, numbered and named capture groups, and a live replace preview — so you can see exactly what your pattern matches (and misses) as you type.

The tool runs on your browser's native RegExp engine — the same engine your JavaScript or Node.js code uses — so results are identical to production. All six JavaScript flags are supported: global (g), case-insensitive (i), multiline (m), dotAll (s), unicode (u), and sticky (y).

The Match view shows highlighted matches in context plus a detailed breakdown of each match with its index and capture groups — both numbered and named. The Replace view lets you enter a replacement string (using $1, $2, etc. for back-references) and see the result in real time. The Library view provides a curated collection of common patterns you can load with one click.

All processing stays client-side. Your patterns and test data never leave your browser. Once you've validated your data format, you can process it with the JSON Formatter or encode special characters with the URL Encoder. Need to validate a UUID pattern you just wrote? Test it against sample IDs from the UUID Generator.

1. Enter a regex pattern in the pattern input. The pattern is shown between forward-slash delimiters.
2. Toggle flags by clicking the flag badges (g, i, m, s, u, y).
3. Type or paste your test string. Matches are highlighted instantly.
4. Review the Matches & Capture Groups section for detailed match info including group values and indices.
5. Switch to Replace mode to enter a replacement string and see the transformed output.
6. Use the Library to quickly load common patterns like email, URL, IP address, and more.
7. Click Copy or press Ctrl+Shift+C to copy the full regex with flags.