Regex Tester
Test and debug regular expressions interactively
Frequently Asked Questions
What regex syntax does this tester support?
This tool uses JavaScript (ECMAScript) regular expression syntax, including all standard flags: global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u).
What are capture groups?
Capture groups are portions of a regex pattern enclosed in parentheses. They allow you to extract specific parts of a match. This tester color-codes each group so you can see exactly what each set of parentheses captures.
Can I use this for find and replace?
Yes. Enable replace mode, enter your regex pattern and replacement string (supports backreferences like $1, $2), and see the result instantly. Useful for testing substitutions before running them in your code.
Is this an alternative to regex101?
Yes. This regex tester provides real-time matching, capture group visualization, and plain-English pattern explanation — all within DevLint's suite of developer tools. It uses JavaScript regex specifically.
Does the tester support lookaheads and lookbehinds?
Yes. All modern JavaScript regex features are supported, including positive/negative lookaheads (?=...) (?!...) and lookbehinds (?<=...) (?<!...), named groups (?<name>...), and unicode property escapes.
Is my regex pattern or test text stored?
No. Everything runs locally in your browser. Your patterns and test data are never transmitted to any server.
Regex Tester: Test, Debug & Check Regular Expressions Online
Regular expressions are built and tested with instant real-time matching by this regex tester — no compile-run-debug cycle needed. Matches are highlighted as you type, capture groups are color-coded, and the plain-English explainer breaks down what your pattern does token by token. JavaScript regex syntax with all flags (global, multiline, case-insensitive, dotAll, unicode) is supported. This tool is also known as a "regex checker", "javascript regex tester", or "js regex online" tool.
Live matching with capture groups
As your regex is typed, matches are highlighted instantly in the test text. Capture groups are color-coded so exactly what each parenthesized group captures can be seen. Named groups, lookaheads, and backreferences all work as expected with JavaScript regex syntax.
Pattern explanation
Not sure what a regex does? It can be pasted in and our explainer breaks it down token by token in plain English. "/^[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$/i" becomes "Match an email address starting with letters, numbers, dots..." — much easier to understand and maintain.
Common patterns library
A built-in pattern library has tested, production-ready expressions for matching emails, URLs, IP addresses, or dates. Each comes with an explanation and test cases, and can be used as starting points.