What is Regex Tester?
Regular expressions are patterns used to match character combinations in strings. This tester provides a real-time environment to write, validate, and debug patterns — with live match highlighting, flag toggles (g, i, m, s, u), and a capture group breakdown panel.
How to use Regex Tester
Enter your pattern in the regex field. Toggle flags using the buttons (g for global, i for case-insensitive, m for multiline). Type or paste your test string — matches are highlighted instantly. The Groups panel shows each captured group by index and name.
Example
Pattern: (\w+)@(\w+\.\w+)
Flags: gi
Test: Contact us at hello@aistacker.dev or support@example.com
Matches: hello@aistacker.dev, support@example.com
Group 1: hello, support
Group 2: aistacker.dev, example.comCommon use cases
1. Validating email addresses, phone numbers, URLs.
2. Extracting data from log files and API responses.
3. Writing find-and-replace patterns for code editors.
4. Learning and experimenting with JavaScript regex syntax.
Frequently asked questions
Which regex engine is used?▾
The standard JavaScript RegExp engine, so patterns behave identically to what you'd use in Node.js or the browser.
Why is my pattern crashing?▾
Some patterns like (a+)+ can cause catastrophic backtracking. The tester catches RegExp errors gracefully and shows the error inline.